3 Link, 4 Link, What Link???

[skullandbones]

OK it's not another thread to talk about which is better just to get your attention!

I've decided to migrate back to the rear of the car for some upgrades that I've been thinking about since day one of the build. At the time just getting it on the road was the priority so now I've had time and money to change the 4 link out for something a little more adjustable. That's the operative word: adjustability. I've decided on a Watt's link after spending some time with James Watt's patent application on his improvements to the steam engine. I'm not sure when it was first applied to suspensions but I'm glad it was. I plan on a style of Watt's link that is mounted on the chassis instead of the pumpkin kind of like the Fays2 that Mustangs use. I have a good reason for that. There are pros and cons for any suspension system depending on what you need it for so I have done my best to design it for street/ auto cross.

I plan on using the quad shock brackets as the main support for the cross member with some added support to tie it to the 2x2 rail above so it will not be fully loaded on the welded bracket. The member will be a simple rectangle with triangulated arms to handle the lateral loads of the chassis. The bell crank or propeller is going to be made of 6061 aluminum with vertical mounting plate that will have several adjustment points for raising and lowering the roll center in the rear. I like that the roll center is exactly where the pivot point of the propeller is so there is no calculation involved. The lateral links and diff mounts are probably coming from Speedway since they have the best variety of pan hard bar brackets I've seen so far.

I like the idea of having the roll center mounted rigid to the chassis so I can adjust it up/down with ride height as well as the cross member adjustment. So the next step is to put the roadster back on the lift for mockup and tacking the pieces then remove and weld it up. This is supposed to be a completely bolt in project so I can remove it if I wish and return to the present system without any modification. Also, I will be driving the car so there will be no downtime as with the front suspension project I did. At some point I will be adding a third link in the center of the diff but the Watt's link will be first. I will in effect be running a 6 link suspension. Then as I've discussed before, I can remove one UCA and do a little experiment to see how the "poor man's 3 link" works. The final goal is to fab a 3rd link that will use the mounting points of the 4 link UCAs (diff and chassis) but in the centerline of the chassis. There may be a few days of downtime when that happens but first things first.

I had to show my pic of the metal I got at industrial metal supply. You can get some great deals from remnants or you can go custom and pay more. I got these for $48 dollar. If I had had the aluminum cut to size it would have been $30 just for one piece. I love a good deal. The shiny aluminum plate is for a dead pedal.


Any thoughts or other input is always appreciated and usually educational.


WEK. :cool: :cool:

[CraigS]

Have you seen this? Good for reference as you design yours.
http://fays2.net/fays2_watts_link_20_.html

[skullandbones]

I did see that eventually. I have looked quite a while but probably wasn't searching as efficiently as I thought. It turns out that what I thought was kind of an odd ball approach to the Watts link is actually the most common application at least for Mustangs. I think Fays2 is the most used by a long margin for the Mustangs. When I was looking at sites and other forums, I got confused, thinking the Fays was mounted on the diff cover but it must have been another one like Whiteline. So I ignored it since I was looking for something different. They mount on the quad shock brackets just like in a Mustang. I'm glad we have those brackets now as I have a good use for them. I believe I can make this work without removing my trunk mounted battery. If I used the Fays I would have to move it. That was one of the things I didn't like about most of the systems out there. I also wanted a clean uncovered diff cover so I can possibly change the gears if I wish. We will see if there is enough space for that once I get mine installed. Of course, that would be after removing the bell crank.

Thanks for the link.

WEK.

[Gumball]

I had the Fays2 set-up on a '65 Mustang I built as a vintage racer - it's a great part and may be of help in designing yours. I think I have some pics of it, but they'll be either old paper photos or on CD somewhere. Let me know if you need them.

Also, a friend of mine has the Fays2 on a car he currently owns - I'd be happy to take some measurement or other photos if you need them.

[skullandbones]

I have a design path already that I had in my head but after describing it to a friend he was nice enough to do a rendering of it from a description which turned out exactly like I had envisioned it. The only critical measurements were the distances between the inside edge of the quad shock brackets at the front which is ~36.25 inches and the length of the vertical members which is ~13.5 inches. That will place the bell crank about an inch below the diff/axle center line at my present ride height. From reading and talking with actual users of the Watts link, that position seems to be a very good starting point. It coincides with the generally accepted height of between 4 and 10 inches above the ground level. I have a pic of that rendering.

I'll include some pics of the real thing when it is tacked and welded.

Thanks,

WEK.

[skullandbones]

I started on the fabrication after cutting the bracket pieces to size (6 x 2.5 inches). The support brackets that ride on the 2x2 frame rails are just some angle cut about 3 inches long. These brackets are set at compound angles so they have to be fitted on the car. I am tacking the bracket pieces in place then measuring and cutting the main cross member to the right width and tacking it up. Since the member will be slightly canted forward at the bottom, I will compensate for the propeller support by installing it on the cross member on a perpendicular plane with the ground. It's turned out to be more challenging due to the close quarters of this area of the car. However, it is going forward slowly but surely as planned. I think I'm opting to have this welded by my friend who has a welding business and can do a much better job on this rather strange configuration. I measured carefully and still managed to weld up the cross member with a 1/4 inch variance from side to side. It probably would have been fine but I undid one side and adjusted it to make it perfectly level. That was a lot of work of a 1/4 inch. Next I will fab the triangulation supports on the cross member and the center propeller support and it's triangle supports. Here some pics.

Thanks for looking,

WEK.:cool::cool:

[CraigS]

I am glad to see the words "triangulation supports" since that was what immediately came to mind when I saw the 4th pic. I am looking forward to following your thread.

[skullandbones]

Craig,

It seems like this is going incredibly slow. I think it's our hot weather. I slow down a lot when it gets above 100. It's not too bad in the garage but if it gets too much hotter the AC is coming on.

Anyway, I thought I would stop and account for what I had done. Then after going back it only took me about fifteen minutes to cut and tack the support bars in. I still have to cut the propeller support into the main member and angle it properly. Some of these little things are quite tedious. I also fit the piece back on the car each time I do something and check the 1/2 bolts for fit. I have to drill six 1/2 holes and tap them for the propeller holes (adjustment positions to raise or lower roll center). So it's off to the hardware store to get new bits. I've been working with aluminum but these steel pieces don't drill as easily. More pics to come.

Thanks,

WEK.

[CraigS]

I am not sure of the wall thickness of your square tubing but are you going to weld in a sleeve for each bolt position? I just looked back at the cad drawing and realized that maybe that piece is solid so no sleeves needed.

[skullandbones]

That's correct. There are no holes in the cross member except the center propeller mount or that would be a real concern with all the back and forth lateral forces on the holes. The center mount is 1 x 1/2 x 8 inches of steel and cut into the member for more welding surface. That mount will be drilled and tapped. It should be strong enough with some triangles built in. I was trying to keep the weight down. So far the cross member is 12.5 lbs. I'm thinking it will be half unsprung and half sprung weight and the CG of the device is pretty low. Once the cross member is in place, I will get a better feel for the lateral link positions. I want to fab the diff brackets off the shock brackets by boxing the bracket and adding a bung. I'm not sure that will work yet (may be too low). The alternative is the ugly axle housing mount that Speedway has. That is a good plan B though. As I said before, the Fays system uses them. I think that was a cheap and easy way to keep the price point down for them. I keep thinking, the only thing that will see it anyway are the insects crawling under the car as there is no good way to view it without putting it on a hoist or jacking it up! Maybe I need a viewing window of Plexiglas in the truck floor. Some people would appreciate it.

Thanks,

WEK.

[skullandbones]

Things are going rather slow but it's summer in AZ so we slow down. I don't see a need for this until I can get a track day or AX next season so it's OK to take my time.

I finally got the cross member tack and sent to the welder. He TIG welded the thin stuff and I wire welded the heavier pieces. So it's cleaned up and painted. Now I will install and leave it in as it will be convenient to measure the other stuff when I put it on the lift. Here are a few pics. I had to angle the propeller mount a little forward at the top to stay perpendicular with the ground. I figured the links and other brackets would be easier to mock up with the cross member finished.

I'm having the machine shop guy do the propeller as he has a milling machine and I don't. That will be the most critical part to get right!

Have to get the propeller back before mocking up the rest with some hiem joints I have on hand.

WEK

[CraigS]

I think you would be better off using a through bolt and nut than threading the holes. If you thread the bolt into a threaded hole your bending load is right on a thread. If you pass the bolt through the hole you can size the bolt length so all the load is on the solid shank.

[Mike N]

Craig is right on that bolt, if you allow the bolt to take shear. Unless you have a partially threaded bolt and the plain shank engages the hole you want the friction at the joint to react the shear and not the (threaded) shank of the bolt.

Obviously pre-load on that bolt is important. Use a good bolt and torque it to 80% of yield. I have a threaded hole on my watts and used one of these http://www.mcmaster.com/#standard-cap-screws/=sjponi

[skullandbones]

Hi guys,

I appreciate the input. This has been a concern from the beginning since it would be the most likely break point in the system. Having said that, I am taking some risk that this will work well enough for the application I have planned. I'm using a 5/8 - 18 screw partially threaded. There is another component that has not been shown because it hasn't been made yet. That is a 1/2 inch spacer between the mount and the propeller. I need that for 1) space to clear the mount and 2) to help close the gap for the lateral links and the propeller to line up in the same plane. There is about 6.5 inches difference so to keep from triangulating the system, I am using whatever little fudge factor I can. The 5/8 inch screw should provide a little more "meat on the bone" so to speak. Don't know for sure if the spacer will help spread the shear load. I think it will but don't have documentation to prove it. Plan B is to redrill/tap the holes for 3/4 - 16. I have a Plan C, also. I did think about what to do in case of failure. I think with a few extra components if the system fails I can attach one lateral link and drive home with a make shift PHB. Anyway, it's something that will get regular attention during the under the car inspection routine.

WEK.

[CraigS]

Take a look at these spacers for a design guide.
http://www.jegs.com/webapp/wcs/stores/servlet/KeywordSearchCmd?storeId=10001&catalogId=10002&langId=-1&Ntk=all&Jnar=0&itemPerPage=60&Ne=1%2B2%2B3%2B13%2B1147708&searchTerm=rod+end+spacers

[skullandbones]

Craig: thanks for the link. That's exactly what I need (shoulder and all).

Installed the cross member for the last time today. It is tight in that space between the gas tank and the diff especially with a rear mounted sunken battery box. It fits and bolted up nicely. I will add another bolt thru the vertical components of the cross member. That would have been nearly impossible with the multiple angles so I will remove the tires and drill though the already existing forward hole on the quad shock bracket. That will capture the main frame of the cross member and add to the stiffness of the unit. The rest of the project is measuring, cutting, and bolting things up. Propeller is being machined except for the pivot hole which is waiting for the roller bearing from McMasters just to make sure of the size (press fit). The car weighs an extra 13.5 lbs now but the benefit is supposed to "out weigh" (ha) the weight.

Note to self: wait patiently for parts.

WEK. :cool:

[skullandbones]

Had no idea I would be getting parts in less than 24 hours from McMasters. I have hear they are fast but that's ridiculous! No complaints here.

Since I have the chance, I mocked up the bearing/sleeve on the 5/8 - 18 screw. I used some hardened washers as spacers and some 0.003 shims. This is the first attempt. I may have to re shim and/or go with a slightly longer bolt to match up with the lateral link brackets. But it doesn't look bad for a first fit. I don't know how much shimming will be necessary to get the right spacing for the sleeve and room to torque the bolt down enough for preload. It's a little like adjusting a wheel bearing by feel except it's a little more tedious. I want the bearing and propeller to move smoothly and still not have enough play to move along the screw shaft. I'll have to trial fit and torque it with some different combinations of shims until I get it perfect. I've heard that any extra play you get in the bearings or spherical rod ends will transmit as a loud "clunk". Sure don't want that.

Propeller should be ready at the machine shop tomorrow.

WEK.

[skullandbones]

Don't have the brackets and other hardware yet. That will be here next Tuesday. So all companies do not ship at the same speed. Unfortunate for a company called "Speedway" should be pretty fast you would think.

Anyway, I did get the propeller back from the machine shop. Love machined aluminum. Here's a couple of pics.

Thanks,

WEK.

[skullandbones]

I received the brackets and rod ends so I did a mock up of the components to check for fit and see how I would have to adjust for final spacers, jam nuts, shims, etc.........

I was very impressed with the clamp on PHB brackets from Speedway. It got a 5 on their top rated list. I can see why. It's a little expensive but for the amount of fabrication it saves, it's worth every penny. The welding was perfect; maybe robotically done. Had to think outside the box by fitting some sleeves under the clamps as the brackets are really for a 3 inch axle housing. A 3 inch 1/8 thick exhaust tube worked perfectly. Just cut it 3.7 inches split into halves and installed under the clamps. I also had to install the brackets in reverse so the orientation of the DS bracket would miss my battery box. It takes care of the bottom link on the watts. The other one is oriented up. There are several adjustment positions with 3/4 inch holes. It's for a PHB so the holes are in a small arc but that's no big deal. I will just adjust to fit when moving the links up or down.

Everything is close since I moved the cross member as far forward as I could when welding it up. So there is a near perfect alignment with the rod ends on the brackets and the rod ends on the propeller. I will have to do some small spacing to clear jam nuts and space the propeller perfectly but it is doable. I used some electrical conduit to simulate the lateral links which I could not order at the time. I needed to measure them with the rod ends installed in the mock up. Those are now ordered. I ended up moving the brackets in slightly from extreme outboard so that the links will be 12 inches long each.

When I lowered the roadster with the mocked up unit, everything cleared at ride height but just barely. In the future, I may replace the cross member with an aluminum clone so I can move it back a half inch then.

Here are a few pics of the mock up. I will have to remove, paint, and re-install when my lateral links arrive.

Thanks,

WEK.:cool::cool:

[skullandbones]

I was hoping for more feedback as there hasn't been a lot of discussion about watts links and how it's affected the handling. I've gotten some on other threads I've done but it's usually a comparison like, "IRS is better for overall comfort" or "here's the hierarchy: 5 link, IRS, 3 link, 4 link". How about when I go into a turn now I know when the rear end is going to let loose. Before it was a guessing game. I'm OK with criticism too. Not the "yellow bullet" kind though. I usually learn at least one thing I didn't know before from these kinds of discussions. So feel free.

Thanks,

WEK.

[Mike N]

Bill, you know my experience but I'll post here for reference.

I went from the 4 link with FFR uppers/lowers with urethane bushings to my own fabricated 3 link plus watts. I had the 4 link for 4 or 5 years before the switch and made many 1/4 mile passes and AutoX runs. For straight line use the 4 link was really never a problem. It hooked well at the strip and handled pretty good on the road. However for Auto X the 4 link was very difficult to find a nice balance at the limit of lateral traction. Once you reached the limit the rear end would almost always break loose in such a way that I couldn't catch it. The rear wouldn't just get into a nice slide it would snap loose.

Many detailed theories out there as to why exactly this is but it seems to be commonly agreed that the 4 link triangulation actually binds up in roll. What this means is that the 4 link rear suspension has an associated roll stiffness in it's characteristics (like a sway bar). So what happens when the rear starts to slide is that the built up roll stiffness releases and unloads the outside tire reducing traction in such a significant way that there is very little chance of saving the rear of the car. There are a few guys who seem to have had success with racing the 4 link but my theory is that they slide the rear of the car in such a way even entering a turn so that the roll stiffness never really gets built up.

Driving the car with the 4 link at the limit you can almost feel the rear of the car raise up slightly as you start to pull lateral G's, and then as the rear end breaks loose you can feel the rear drop slightly. This doesn't happen with the FFR 3 link plus panhard bar or a watts link in place of the panhard bar. For anyone who does anything more aggressive than cruise around in their FFR (and who doesn't?) just about any upgrade to get away from the 4 link 'bind' will provide a very nice improvement in the way that the rear of the car behaves under cornering loads.

I'm waiting to hear Bill's reports on how the watts behaves with the 4 link still in place. It may actually introduce another source of binding that could make things worse. A partial fix is to remove one of the upper links (poor mans 3 link).

[skullandbones]

I'm just waiting for those lateral tubes. I may have to get a couple of things from McMaster as well but it should be possible to do some preliminary testing within a week or so.

Re: the guys sliding around the turns sounds like a pretty good work around. Maybe they are drifters so it comes naturally. Also, I find it interesting that you stayed with the 4 link as long as you did. I have had a lot of motivation to change earlier than later mainly from the discussions here and on ffcar. I know the 4 link gets bashed a lot due tot he design shortcomings but it is OK for a lot of uses and is very simple and reliable.

I will as promised try the "poor man's 3 link" but I will do some driving with the "new 6 link" when I finish the Watt's link. I really can't wait to see if the PM3L really works. It does on many Mustangs according to the forum so it should with this application too. We will see.

One more thing: I was wondering if the third link (when I fab that portion) should be a bit heavier than the lateral links on the Watt's link. I was thinking of a 1 or 1.25 rod end. Does that sound like overkill or sound reasonable. I was going to possibly use the tube/rod ends for the PML experiment. I might have to shorten the tube or change to a much shorter tube but I could still use the other parts for the final third link. Any thoughts?

Thanks,

WEK.

[Mike N]

Bill, I used 3/4" rod ends for the suspension links and 5/8" for the watts. The 3/4" are plenty strong enough.

[skullandbones]

OK, Mike. I will go with the 3/4 rod ends. It's funny that Speedway has the larger rod ends but don't seem to carry the larger tubes to fit them. Maybe it's on their website. The catalog probably can't hold all the parts. I'm finding that the choice of certain components can complicate the process by having to make accommodations for them when they create a clearance issue. But that's why it is so much fun, right?!!!!!!

Thanks,

WEK.

[CraigS]

I am pretty sure that the FFR 3rd link and panhard rod are 5/8 rod ends. I know the jam nuts are 15/16.

[skullandbones]

That's great to know. So the 3/4 rod ends should be fine. So Craig: do you have any insights to share about your 3 link? Is it an FFR 3 link? I've heard a lot of good stuff about them but not too much negative. I'm headed in that direction with my watts link which will substitute for the PHB.

Thanks,

WEK.

[frankeeski]

I was hoping for more feedback as there hasn't been a lot of discussion about watts links and how it's affected the handling. I've gotten some on other threads I've done but it's usually a comparison like, "IRS is better for overall comfort" or "here's the hierarchy: 5 link, IRS, 3 link, 4 link". How about when I go into a turn now I know when the rear end is going to let loose. Before it was a guessing game. I'm OK with criticism too. Not the "yellow bullet" kind though. I usually learn at least one thing I didn't know before from these kinds of discussions. So feel free.

Thanks,

WEK.
Bill, I'll try to be kind but just remember you asked for it. Your 4-link with Watts link is not going to react any different than the standard FFR 4-link. I can't predict but it might even perform worse because of the inherent arch the upper control arms react in and also the stiffness of the poly bushings. I applaud all those who choose to look outside the box and fabricate themselves. I would however ask why you didn't just go with a pre-fabricated piece like the FFR 3-link or a Levy 5-Link? When you consider all of the parts you are buying and /or having fabricated by outside fabricators I just wonder how much money you've saved? Again, I get it, I fabricate much of my own stuff. Moving on, I haven't seen Mike's setup but I know he also fabricated his own Watts link setup. I have the Levy 5-link with the billet aluminum upper and lower control arms with Heim joints on both ends of each control arm. This system offers suspension flexibility that the FFR solid poly control arms will never be able to compare to. Granted, on the street the system will never see the limits of the Heim joints. The 5-Link is the best riding suspension out there for the FFR provided the proper springs are used, the rear suspension has no bind whatsoever. Now you could do a 6-Link, as you are calling it, but to do it right you would need to use control arms with heim joints on both side of all of the control arms. That would give you the flexibility in the suspension similar to that of the Levy 5-Link. The next thing I am going to tell you is to ditch the FFR springs on the coil overs. The rates on the springs is far from consistent. When corner weighting the car with the FFR springs we found close to a 70 lbs difference in the rear #350 springs and 50 lbs difference in the front #500 springs. I switch over to Eibach springs and they were within a few pounds of one another or close to perfect. On a car with a chassis as stiff as the FFR is, a 70 lbs difference is huge. I also dropped the rears down from 350 lbs to 250 lbs and the fronts from 500 lbs to 425 lbs. I know this goes against the conventional track wisdom but with the front anti-swaybar the car plants well and the 5-link keeps the rear on the track surface as well. Running 18" wheels and tires the drop in rating also give a bit better ride on the street. The last thing I would tell you is that tire pressure is a huge issue with the dreaded snap spin. 1 lbs of pressure for every 100 lbs of car is a good starting point but not ideal. Tire wear is going to tell you what pressure to run your tires at. The sweet spot on my 18" tires for the street is 18 lbs in the rear and 19 lbs in front. Track temps allow a little bit less pressure. Mike is a great resource, he has allot of track time so keep his # handy.

[Mike N]

Frank.

My rear set up is very similar to Gordon's. I am a tinkerer as you know and I studied, CAD modeled and analyzed the rear suspension and as a result there were a couple of things I wanted to do a little differently to Gordon's. I'm very happy with the result. Even with a couple of pieces that I paid to have machined I have less than $600 in my rear suspension. Of course I have about 100 hours of fab time in it so it wasn't 'cheap' if you include labor.

I'm curious to see how Bill's rear suspension works with the watts link and 4 link. With the soft rubber Ford bushings I have a feeling that it might actually work quite well. I'd love to make a couple of auto X runs with the watts disconnected and then a couple with it in place to see what sort of changes it makes.

[skullandbones]

Hi Frank,

You were right, I haven't saved a lot of money by doing the DIY version of the watt's link. I may have about $550 in it with some extra parts and metal left over in the project. I did it mainly as I needed a customized cross member to fit with my sunken battery box. Did not want to change that an re-route electrical at all. Fays2 was a good value but just would not work. I also wanted a strictly bolt in system. So far that is following plans. My plan was to go from the 4 link to the "6 link" for a short time period to experiment. I don't expect any life changing results but it will be interesting to have that knowledge. I feel the 4 link is severely limited by design so fixing it is unlikely. However, adding the rod ends to everything would be another interesting experiment. I don't want to invest that much in parts and modification of the UCAs and LCAs to prove it. Sticking with the transitional aspect, I will try the Poor Man's 3 link which will consist of removing one UCA. I think that will be most interesting. It would be nice to stop there if it worked well except for changing the UCA for the sphericals and swedged tube. If there are observable limitation to this setup, then it's on to the custom 3rd link mounted off the old 4 link brackets. This is easier for me as I do short projects much better. I noticed from a picture of Mike's system that he migrated to lower control arms that fully articulate. So that is a logical move, as well.

This was supposed to be a summer project so I think it will take most of the summer to evaluate this stuff as we don't have a lot of opportunities to get out in this heat (my personal opinion). I hope to have enough progress made by the time I track down an AX event that I can benefit the most.

I told you I always learn something from these conversations. I did not know that FFRs springs varied that much from published values. I have a MKIII with 450/250 front/rear springs. The kit was delivered on Apr, 2007. So I don't know where FFR was getting the springs they included in the kit. I'm a little early in the process to worry too much about them as I have lots of other "fish to fry" for now. Thanks for your data and input. It will be considered as I get deeper into the project.

Note: Would you mind how you are measuring the spring rates?

WEK.

[CraigS]

I went from 4 link to ffr 3 link. The first most obvious change was that the car rolled more. This is to be expected when you lower the roll center. It was also much more stable particularly in entering corners. I wouldn't say that a surprise over steer couldn't happen but it seems to be more gentle when it does.I quite soon added a vpm rear swaybar. There are a couple of things to look at in the rear suspension. I'll call one the rear view which is where roll center shows up and affects how much the car rolls and also the handling balance when compared to the front roll center. The other is side view. The angles of the links determines anti squat and roll steer. Of course these overlap in real world driving since you are often cornering and, either accelerating or decelerating, at the same time. One thing to note when comparing an ffr 3 link to a similar setup but w/ a watts link. In theory, if the roll centers are the same, the handling should be the same w/ either the watts or panhard. One advantage to the watts is that the roll center stays the same in either a right or left turn. A panhard varies in right vs left depending which side is mounted to the frame. A disadvantage to the watts comes when you want low rollcenters. The height of the panhard determines RC in that setup. But the height of the propeller pivot determines RC height in the watts. But you have the lower half of the propeller hanging below the RC, so that limits how low it can be.
WEK said... "I feel the 4 link is severely limited by design so fixing it is unlikely. However, adding the rod ends to everything would be another interesting experiment. I don't want to invest that much in parts and modification of the UCAs and LCAs to prove it"
Sure wish I could find it again but 4-5 yrs ago I saw one of the top Mustang aftermarket firms mocked up a 4 link w/ rodends in both ends of all four links. They found that the rear axle wouldn't roll at all. The original design needed rubber bushings to work.

[skullandbones]

Hi All,

I have heard some individual reports of bad behavior of the 4 link that goes away when changed to another type suspension. One thing that Mike mentioned was that he noticed less skittering (paraphrasing) on wash board with a 3 link. I guess that means it's staying on the ground a little longer than with the 4 link. Craig you are saying the rear end movement is more predictable. I have a question. At what speed (minimum) and type of turn will give you the first indication that there is a real difference? When I'm driving the roadster it is so stiff, it doesn't feel like it is giving at all. I know it is but there doesn't seem to be much movement like dive, squat, or roll in any direction. Maybe it will be easier to recognize than I think but right now, I have no idea what to expect.

Regarding the 4 link experiment with the hiem joints, I wonder if they used rod ends that will take a lot of misalignment. The "rock ends" that Speedway carries are made by QA1 and operate at a misalignment of 36 degrees. The rod ends I have for my watts link do not articulate very much at all. However, they are nearly perfectly aligned and don't need that travel. I can see how that exercise would fail miserably if they didn't use the right stuff. It would probably bind worst than the bushings.

Thanks for the accounts of your exploits!

WEK.

[Jeff Kleiner]

Bill,
RE: the lack of roll or movement with rod ends in the control arms. No matter how much articulation the rod ends allow with the splayed upper arms it becomes an impossibility for the axle to move freely in any axis other that straight up and down...think of it as a triangle with the chassis forming the wide leg at the forward mounts and the two UCAs creating the other sides, meeting at the axle. The wide base (chassis mounts) is a fixed distance. If you were to try to raise one side of the axle one of the arms would have to get shorter while the one on the opposite side would have to get longer. Obviously with solid arms and rod ends that can't happen (well, without bending things anyway!). With rubber or poly bushings the compression & extension of the upper arms as they move through varying motions occurs in the bushings themselves. When those bushings reach the limit of their allowable movement the suspension binds fully and changes the loading of the chassis which usually produces that much referenced snap spin.

Jeff

[skullandbones]

Jeff:

That's a good way of looking at the problem in the design. I've seen 4 links that worked a lot better than this one (racing and hot rodding) so when I saw the "Mustang" 4 link on my roadster when I was assembling it, I thought it rather odd. My logical side was saying, can this even work? So I guess it is what it is. That's why I will be going to some type of third link eventually. I'm hoping I will be able to figure out a good fabrication for the mounts. They present a great solid platform but they are arranged at odd angles so it will take a little bit of imagination.

I don't know where the ideal location is for the roll center for the rear end of this car but I am betting that it is just south of the centerline of the pumpkin/axle. That's why I followed the other style watts link systems out there and put most of the adjustment for the bell crank higher. I also have a little limited adjustment on how far I can move the lateral links to match the location of the pivot point. The clamp on brackets have 6 adjustment holes but they are pretty close together. We will have to see how it plays out.

Thanks,

WEK.

[skullandbones]

Received the tubes for the lateral links and started putting it back together for the nth time. What I spent most time on was rearranging the spacers, washers, and shims on the bell crank to get it functioning without too much play (hand fitted) and clearancing the rod ends at the axle brackets and the bell crank. The last surprise was when I lowered it to the ground. One of the lateral links does not line up like I expected so that will have to be moved to another adjustment point. I think getting the links lined up for each adjustment will take some documentation so I don't waste time doing by trial and error. I probably won't need the full range of adjustment but being able to raise/lower the chassis and adjust the bell crank along the 7 adjustment holes on the cross member is an advantage. Once the lateral link is moved to get it parallel, I will do my first test drive. I found a place to do a test drive. Will do a video to give you a look. Thanks, WEK.:cool::cool:

[CraigS]

I haven't done a re- research of Watts links but, as I remember it, the links do not need to be absolutely parallel to the ground. The RC is determined by the height of the propeller pivot and not by the link attachments to the axle. Of course, w/ your style of attachment to the propeller, you need them well aligned so the rod ends don't bind. As quick tests, I think you could move your propeller up or down one hole w/o moving the end attachments. BTW, the RC on the FFR 3 link is about at the height of your lower propeller link in the second pic when the ride height is somewhere in the 4.25 area. So your RC as shown is somewhat higher. BTW2. Sorry I can't give more details as my last 4 link to 3 link conversion was in 2008 so memory of details is gone. I had done it first on my MkI in 06 and then wrecked that car in 07. In 08 there was no question I would also do the MkII I had bought. I did run a couple of autocrosses w/ the 4 link. Ran pretty soft rear springs (250?) and all rubber control arms w/, I think, 550 front springs and a 3/4 front bar. The car wasn't terrible that way but that was back when I was running street tires so it wasn't very good test.

[skullandbones]

Today was the first day back on the road after installing the watts link. I found out by accident (should have figured it out before) that the clamp on axle PHB brackets become mirror images of each other when you invert one. So I had not figured that out until after a couple of adjustments with the lateral links. Long story short, I can put the rod ends in the bottom bracket hole on each side (or 2 up on each side, 4 up on each side) and it puts the links in the correct position. It was a happy accident I guess that the spacing between the two brackets matches well with the length of the bell crank. That's nice!

I drove about 40 miles today on varying surfaces and some freeway driving. The object was to see if I have any issues with the installation as far as rubbing, binding, etc..... There was no evidence of that. I still have to raise it on the lift to check for any damage or rubbing but it was super quiet in the rear for the entire time. I didn't expect anything spectacular as it is the same 4 link with the added watts link or my first "6 link". There were two instances when I felt like there could be some change but it's too early to be sure. One was when rounding the tight curves in my neighborhood. I tried taking them as quickly as possible without sliding too much. I think there was a little difference in the way the whole car rounded the curve. It just seemed more precise and I had trouble getting it to slip sideways at all. I was not at high speed but faster than you would drive it normally. I also noticed on some wash board and loose gravel that the car did not skitter around like it has in the past. I am reserving judgment on making any definite claims until I can remove the watts link and drive the same territory tomorrow or the next day. There is a cool drive with finished streets and no houses and a circle I can use as a "test track" but today the sheriff's deputy was using it as a radar post so I couldn't take the opportunity.

I didn't notice any negative feedback from the rear suspension from this little drive. But I really can't absolutely confirm any differences until I check it with just the 4 link and then again with the watts link hooked up. I'm hoping that I will see some variation between the two setups. After that, we will go on to the Poor Man's 3 link to compare that change.

Thanks,

WEK.

[skullandbones]

Took the roadster out for a drive with the Watts link disconnected. So I've had one drive with and now seeing if I can tell any difference. I rubbed bar soap in the inside edges of the fenders where they would contact the tires. There is a 5/8 inch space between the fender edge and tire at ride height. I have not experienced any tire rub on compression, rebound, or against the fender so far. This was just to verify that the tires were not hitting the fender even a little with lateral forces applied. I saw no white tire marks and honestly after driving the roadster once with and once without the Watts link within a day that I can 't really see a difference. If there is, it is not significant. So I will make another pass with the Watt's link attached (then it will remain installed) just to check again. My goal is to transition to a 3 link in steps but this will give me some evidence if asked about the experiment in the future. Right now, I would have to say the Watts link doesn't have an effect either way with the 4 link. If I had the place to test it (higher speeds safely), I would see if the Watt's link helps to reduce the chances of a "snap spin" but that is not doable at this time.

WEK.

[skullandbones]

Took another drive. This time with the Watt's hooked up for the final time. After two days of on and off the lift; attaching and un-attaching links, my conclusion based on the three drives is that the Watts link does not have a significant effect on the 4 link suspension. I will now go forward with my plan to fabricate a 3 link that will replace the UCAs on the 4 link. However, there is one more step before the change to a custom 3 link. There has been discussion about a suspension solution that the Mustang community has used called the "Poor Man's 3 Link" (PM3L) which consists of removing one of the UCAs of the 4 link. Since the suspension points are the same as a Mustang's, I thought I would do it. Of course, this requires installation of a PHB, Watts Link or some other lateral link that will stabilize the lateral motion of the chassis. I decided to try out the PM3L since it was the next logical progression toward a 3 link. I will be fabricating the brackets for the third link while I am driving the roadster with this change. I'm using the ends from the UCAs for part of the bracket so I will have to stop driving for a while when it's time to weld up the differential bracket. The diff end of the UCA will be used on the OEM bushing attached to the diff with a bar welded across the top of the diff to connect the two bushing brackets. A tab on top and centered on the diff pumpkin will receive the spherical rod end at the diff connection point. Another bracket will use the connection points of the UCAs at the chassis side with a similar tab for the other spherical rod end and link that make up the third link. The third link will be app. 10 inches long. My plan is to make it as level as possible with the ground to avoid any pinion angle issues. Not sure how long it will take me to finish the fitting and welding as it is tight and tedious in that area. But I will be driving with the PM3L until the custom link is ready. Thanks,

Note: one reason the PM3L may work better for the roadster is that the attachment point is directly connected to a frame. On the mustangs inherent weak points were where the UCAs attached to the unibody. Serious racers usually had to reinforce those areas with backing plates. Even if the PM3L works, it is just a temporary setup. Wish me luck!

WEK.

[CraigS]

I wouldn' t use two ends from the 4 links. You need at least one end w/ a rodend so the car can roll in relation to the axle. Here is a source for steel and aluminum threaded tubes etc.
http://www.afcodynapro.com/store?search_api_views_fulltext=threaded+link+tube s&=Search+Store

[Mike N]

Bill

Your top link will be quite short and even though roughly the same as the factory upper still not ideal. Because of the difference in lengths of the lower and upper link the pinion angle will change with suspension travel. I don't know that this will be an issue or not. I agree with Craig, rod ends would be my choice to the upper link ends.

By the way I don't think you would expect to feel any real difference with the watts until you get to the limits of lateral traction. Any big empty parking lots near you?

[skullandbones]

Check out the pics from post 38. That is where I am using the UCA flanges that I cut. They will mate to the bushings so it should be a perfect fit (with a little spreading). I also wanted to use them to reduce fab time and add a little dampening to the system. It will have less than the 4 bushing 4 link but still some. The chassis bracket will be mounted steel to steel. So I was planning on using the spherical rod ends. Don't want any binding in the system. I may do rod ends on at least one end of the lower control arms later. That would also give some alignment adjustment if needed. Thanks for the additional Afco source. I have been using Speedway but I will check around.

Regarding the length of the upper third link: I do have concerns about that. However, the 4 link has been operational on my roadster and works fine. I don't experience any pinion angle issues. So I am thinking the similar length link should work. I will do my best to extend the length of that. I think I might fudge a little and get as much as 1.5 inches. That would put it at about 11.5 inches. Mike, what is the length of your upper link? Also, FFRs third link can't be that much longer than mine since there is only a limited space to work in. I know they cheat by putting it further aft but not that much. I guess the unknown after changing links will be to make sure pinion angle is OK. I will do pics and measurements lifted and at ride height as it is now to make sure I can get back to that setting when I make the change.

I appreciate the critical thinking and input you guys give as it is, in my opinion, a real strength of this forum. It never hurts to have multiple pairs of eyes on the subject matter to get to a conclusion. I know it keeps me focused on the task at hand. Thanks again,

WEK.

[skullandbones]

Got a chance to drive the roadster with the left UCA removed today. It is my first experience with the "Poor Man's 3 link" used on many of the Mustangs. I have not seen a lot of difference with the prior small changes with the watts link and the 4 link in combination but today was totally different. It works! The PM3L really works! I will continue driving the car like this for a while until I get my three link brackets and other link components. I was pretty skeptical about whether it would work but after experiencing it, it makes sense. Even though the upper link is on a severe angle, geometrically it works against the other control arms just fine. I tried it on regular driving and a little more severe curves and accelerations from a stand still to roll offs. I didn't hear any unusual noises or rubbing and no drive shaft related sounds. It was also OK as far as tires rub. What I noticed right off was a softer ride. I hope I can report some specific behaviors as I drive it for the next couple of weeks that will make more sense.

To answer your question Mike, no I can not find any large parking lots that I feel safe enough to do donuts and such. If I do that around this area, the good ol' boys will have me eating asphalt and impounding my roadster. So I will have to find a place like a track. But I'm pretty happy that things have gone as they have so far. Next task is to complete the third link and try it out, too.

Thanks,

WEK.

[skullandbones]

A friend and I took a mountain road trip about 40 miles yesterday (early and the temp was down a bit). This was good because it allowed me some more time to try out the Poor Man's Three Link. It was very well behaved and rode very smoothly at speed and up and down and around the mountain curves and hills. I only have a few more days to get final impression of this setup. Never planned on keeping it this way but want to be able to say for sure one way or the other.

Started fabbing the chassis bracket and although the other 4 link UCA was still in place, I was able to get a pretty good mockup of the bracket by using the left side as a template. I used the vise, cutoff saw and 50 lb anvil to shape the 3/16 inch angle bracket. When I receive the welding tabs for the 3 link and the other link parts I will remove the UCA (never to be installed again). It shouldn't take long to do the final fitting since I have done a lot already. Here are some pics of the bracket and the PM3L.

Thanks,

WEK.:cool:

[skullandbones]

One interesting thing I discovered about the third link today was a "rule of thumbs" or standard, I guess you could call it. It was a general article about the 3 link and it's strengths and weaknesses. It mentioned that the top link should be about 70% of the length of the lower links. So The FFR lower links are about 17.6 in and the upper link is about 9.25 in. My best estimate for the top link for my custom setup will be app 11.5 in. 70% of 17.6 would be about 12.3. I won't be able to do that but I think at about 65% is not bad at all. So hopefully this will improve the geometry a little. WEK.

[skullandbones]

I disconnected the other UCA and started the modification of the UCA to attach to the three link bracket that sits on top of the diff. Here is where I have lost an important measurement. When I removed the UCA, the pinion must have drooped some. When I took the measurement for the length of the three link arm, it was quite a bit shorter than my initial measurement at initial mock up. So now it looks like I will have to rely on my initial measure to hook up the three link. My concern is to get the pinion angle right. I think I did an initial pinion angle measurement when I installed the 4 link (way back when). I'm sure it was within specs then. I was not concerned that it was something I had to bother to a great extent since I was using a basically un-adjustable suspension. I trusted FFR to get it right and it did work. With the FFR 3 link installation instructions, it says to use 2 degrees for a little more motion of the 3 link suspension. So my question is: especially if you have gone from a 4 link to a 3 link of some kind, what did you end up using for your new pinion angle?

I don't want to blow up my drive shaft into a million pieces so I really could use some feedback. Also, how is the best way you have found to measure. I can't find a great way to tell if the diff is level. There is a small ledge running fore and aft along the pinion shaft. That is the flattest and only level looking place on there. I would like to get the trans tailshaft angle and pinion angle the same relative to the driveshaft. I've heard that is best.

Thank you,

WEK.

[Jeff Kleiner]

When we speak of pinion angle we are referring to the pinion shaft relative to the transmission's output shaft. When determining pinion angle you can leave the driveshaft on the workbench, and in fact if you follow my method described below it will be easier if you do just that :)

Don't get caught up or confused on any thoughts of horizontal. It doesn't have anything to do with the angle of the driveshaft or the engine and trans being level with the earth or chassis. Think of it this way; when looking at the car from the side if you were to project one line from the transmission output forward and another line from the pinion shaft forward with your pinion angle at zero they would be parallel. If you put any angle to the pinion the two lines are not parallel and would get farther apart as they go forward. If the pinion were to be angled UP (relative to the trans) it's line would be above the output line and get farther above it the farther forward it went. If it were angled DOWN it would be opposite---the pinion line would be below the transmission line and get farther below as it went forward. To set the pinion angle so that it is angled down below is what we're after . Clear as mud?

My method for ease of measurement:
Set ride height then put the car on jackstands so that the axle is loaded. Once again, we don't care if the frame is dead nuts level; we're only going to look at the difference between output shaft & pinion shaft. We know that the crankshaft and trans output shaft are parallel therefore the face of the damper/ crank pulley is perpendicular to the output. We also know that the pinion flange face is perpendicular to the pinion. See where I'm heading? I've always found that it is easier to get a good measurement with the magnetic angle finder by reading vertically on the crank pulley/ damper and pinion flange rather than trying to work with the horizontal shafts themselves. Once you can see the two angles you can then calculate the difference. Generally with these cars we want the pinion down somewhere in the vicinity of 2 degrees (once again, meaning the input is pointing down in relation to the transmission output shaft). Reason being is so that when the axle tries to rotate it's input upward under acceleration the pinion angle becomes less. This rotation is especially more pronounced on a 4 link car using the soft rubber bushings in OEM Mustang arms vs. a 4 link car with poly bushings or a 3 link with polys in the lowers and the solid upper link.

Three link adjustment is easy; simply alter the length of the upper link. If your pinion angle is less than 2 degrees you would shorten the upper link to roll the nose of the diff downward or if it's greater than 2 degrees lengthen the upper link to bring the nose up.

Hope that all makes sense and good luck!

Jeff[

[skullandbones]

Jeff,

Just to make sure I'm understanding the terminology, when you say pinion flange do you mean the gusset like projection running fore and aft on both sides of the pinion shaft? That is what I was describing as the only level place on the diff I could find. I realize you don't need to be level though. So if I measure the pinion shaft angle by setting the angle guide on the ledge and the crank/pulley angle say on the crank shaft pulley and take the difference, it should be the same no matter if the car is level or not. Is that essentially correct? I hope so.

Thank you as usual,

WEK.

[frankeeski]

Jeff,

Just to make sure I'm understanding the terminology, when you say pinion flange do you mean the gusset like projection running fore and aft on both sides of the pinion shaft?

Thank you as usual,

WEK.

No, the pinion flange is the flange that the drive-shaft bolts to on the front of the pinion gear snout.

[skullandbones]

Oh yeah. That makes sense. Thanks, Frank! Also much more accurate surface to measure.

Also, thanks, Jeff. I will try to get some measurements this evening when it cools off a little.

WEK.

[Jeff Kleiner]

Frank's got it! This is one of those things that many builders seem to fret over unnecessarily but is really simple to check and adjust. Good luck with the rest of your project!

Jeff

[skullandbones]

I finally finished the components for the custom three link so I could clean them up and paint everything. So that's everything I needed to mount the third link on top of the pumpkin.

This is a completely bolt in project. The bracket on the chassis uses the old 4 link pickup points and it mounts steel to steel with 4 1/2 inch bolts. The differential bracket mounts using the OEM bushing brackets with the same bolts that were used on the 4 link. To add some stiffness to this bracket, I added some steel strap supports that run down to the pinion housing. There is a very little flexing with the bushings but not much.

Finally, I had to jack the pinion up with a jack as it had drooped a lot. Then it was pretty easy to put the third link into its flanges to hold the diff in place.

Now I will lower the roadster to see how the links settle in. I think I may have to shorten the third link a bit but I will lower it first to see. The 4 link was static in that it did not have adjustments to change the pinion angle so this new link may not be perfect. It looks like it may have pushed the diff back a little so that the watts link clearance is in question but it's hard to tell when the suspension is drooping.

Hey guys how does the drive shaft look? That's another reason I'm thinking I may have to shorten the third link a little so I will have some adjustment range. Right now I can't bring the pinion down any more until I shorten the adjustable tube on the three link.

It's a pretty tight fit under there. Can't wait to get this out tomorrow and see how it feels.

Thanks,

WEK.

[Mike N]

A couple of observations. The attachment points for the 3 rd link are offset from the attachment points to the frame and pumpkin so you will generate a torque that will roll the cross members about the attachment points. The bent tabs you have on the chassis cross member to frame interface are not very stiff or strong and will likely need boxing in. The pumpkin cross member will need something more substantial than the two straps that you currently have in there to resist the rotation. Best case you will just get a lot of flex under load which will give you screwy handling at the rear of the car, worst case something might break or bend.

[skullandbones]

Hi Mike,

The pickup points of the link itself are centered on the chassis and equidistant from the attachment points on the diff also centered. I guess you aren't talking about those. So will one cross member be affected more by the other or do they affect each other equally badly? I am seeing two force radii that have different diameters, if you will, generated by the 4 pickup points on the chassis (at the 4 link mount location) and the diff (also old mount location of the 4 link). Is that an engineering no no? Is that just an inevitable thing that you have to deal with by over sizing the cross member to compensate for the issue? I can strengthen areas if they need it. Thanks for your observations! WEK.

[frankeeski]

The pumpkin cross member will need something more substantial than the two straps that you currently have in there to resist the rotation. Best case you will just get a lot of flex under load which will give you screwy handling at the rear of the car, worst case something might break or bend.

I'm with Mike. You're asking a lot of those thin metal brackets. You really need to box them at the very least. As for the pumpkin brackets, I think you need to go back to the drawing board and design something a bit stronger and less flexible.

[skullandbones]

Well Frank and Mike,

I don't know why I didn't think about adding a gusset at the end of the chassis cross member. While I was at it, I could have put a couple under the weld tabs to stiffen that as well. Oh well.:mad::mad::mad: I think I was satisfied that the upper plane of the angle steel was supported by the bolt on bracket on top and the bent tab also bolted with a 1/2 inch bolt would support that plane so in effect "boxing the structure via the mounting method. But I guess it would not hurt to have the gussets. The only problem is that I had to work that cross member in like it was a Chinese puzzle. It's very close tolerances due to the compound angles of the 4 link pickup points. Now that it is place, I think it will be easier to get those pieces welded in knowing that the rest of it fits OK.

Frank: the cross member on the pumpkin will have a little flex as I am using it with the stock Mustang bushings. It should have less flex than the 4 link links. I will need to strengthen the support straps. I guess I will have to break out the acetylene to bend some 1/4 inch straps in their place. At least I have a template to go by. Also, if it turns out that the bushings give to much flex in the system, I have measurements for solid bushings that I can replace to take all the play out of it.

The operative word here is: Prototype! I'm pleased with the way it's turned out so far and I appreciate the opinions and observations to help me stay objective and on task. I will report back to see how well it works so far. I spent some time this morning adjusting the third link. It's about ready for a test run.

Thank you,

WEK:cool::cool:

[Mike N]

For the front mount extending the mounting ears up to the 2 x 2 behind the seats will give you a very robust mount. This is similar to what FFR does with the bolt in 3 link upgrade. Here's how I did mine.

32610

[frankeeski]

I do like the way Mike did his upper link mount. Gordon's mounts to the upper 2"X3" rectangular tube with 4 bolts. I also welded mine as well for good measure.

WEK, I think you should try to use some rectangular or round tube for the pinion supports up to the Diff link mount rather than the flat stock. You'll get less flex. Heck, even angled stock would be better. And get rid of those rubber bushing sooner rather than later. They are a ***** to remove.

I've heard of a bunch of way to remove these even burning them with a torch But this way worked well for me.

With a hole saw slightly smaller than the metal part of the bushing, drill out the rubber

Then cut a relief in them with an angle grinder and a cut off wheel.
http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/012.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/012.jpg.html)
Then use a chisel to fold them into themselves.
http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/013.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/013.jpg.html)
Then beat the hell out of them with a hammer and viola!
http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/015.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/015.jpg.html)

[skullandbones]

Thanks for the bushing removal piece. I'm sure that will come in handy for me when the time comes and others as well.

I thought on it about the pinion supports which are 1 1/4 x 1/8 steel straps. I think I will add some 3/4 in square tube to those by welding them to each other. It will be much faster than shaping new ones and drilling holes.

Curiously: I looked at the drooping pinion angle and decided that I needed to shorten the third link tube so I took a couple of pieces off each end (total about 3/1-4 inch) and then realized that I was thinking backwards. Actually, the tube needed to be longer. So I can use it for now but will have to order the same tube again as it was the perfect length as I had estimated in the first place! I really thought I would be adjusting less pinion angle to get to an acceptable number. But it turns out that I'm adjusting more into it to get to where I need to be (diff not pointing up too much). What are the best numbers for this when you are at the 350 to 375 hp level with a three link?

This project has been a lot of fun for me to get to know the "ins and outs" of the rear suspension mounting. I know the performance end of it is an entirely new and complicated aspect but at least I can play that game now.

Thanks,

WEK.

[Mike N]

The key is that under load the pinion angle should be zero or close to zero. With rubber bushings in the set up there will be more flexing than with rod ends or spherical joints. I have 'hard' joints everywhere and set mine up at about 0.5 degree down under the assumption that even without any rubber or urethane bushings that there will be some small amount of flexibility. With the factory rubber bushings you could get a couple of degrees of movement pretty easily.

By the way don't underestimate how much load that upper link and the attachment points (may) have to take. To work with round numbers assume that the CG of the FFR is 4 ft forward of the rear axle (I know it's less) and your car weighs 2500 lbs (many weigh more). In order for the car to pull a wheelie you will need to apply 10,000 ftlbs (4ft X 2500lb) of torque at the rear axles. If your upper link is 1 ft away from the axle centerline you will be reacting roughly 10,000 lbs (10,000 / 1) through that upper link to pull the front wheels off the ground. I designed mine to have a margin of safety of more than 3 (>30,000 lbs). I agree that this may be a little bit extreme but even with crappy street tires you will still be reacting 1,000's of pounds of load through that upper link, brackets and frame.

[Jeff Kleiner]

What are the best numbers for this when you are at the 350 to 375 hp level with a three link?



Post #46...

Jeff

[skullandbones]

I missed that statement: Generally........vicinity of 2 degrees........ Apologies.

So if I have a setting similar to what you discussed say at 2 degrees down relative if my system operates between that and 0 up to 2 degrees pinion shaft up, I should be OK. I'm thinking the universal should not "know the difference" between 2 degrees down or up. I haven't measured to see where the bearing caps start to strike the drive shaft yoke but I don't want to be anywhere near that point. Does this 2 degree down also apply to the FFR 3 link? It looks like with the solid attachments and all, they could be closer to 0. Mike says he's running about 0.5 down on his 5 link, I think. If I choose to go to solid bushings and stiffen up the supports, maybe that would allow to bring those tolerances in a little (not sure).

There is one other thing. I was under the assumption that the third link would have more stress on it under acceleration than decelerating or braking. Is that true or false? If false then I definitely will need stronger straps on the pinion cross member.

Thanks,

WEK.

[Mike N]

There is one other thing. I was under the assumption that the third link would have more stress on it under acceleration than decelerating or braking. Is that true or false? If false then I definitely will need stronger straps on the pinion cross member.


There will be less weight on the rear of the car under braking due to weight transfer (forward) so the limits of traction will be lower so the loads will be lower. However the 3rd link will be under tension and those straps will be under compression during acceleration so they need to be much beefier. They need to stop the tubular cross member piece from rotating forward so it's bending strength too.

[skullandbones]

There will be less weight on the rear of the car under braking due to weight transfer (forward) so the limits of traction will be lower so the loads will be lower. However the 3rd link will be under tension and those straps will be under compression during acceleration so they need to be much beefier. They need to stop the tubular cross member piece from rotating forward so it's bending strength too.

I took Mike's advice about the 1/8 inch metal straps and welded a 1x1 square tube to each strap. The straps are 1 1/4 inch so there was room for welding. I sure this will be stiff enough for the design. I first had decided not to add the supports at all but had second thoughts but did not think it thru completely. So it's good to be exposed to the rigors of the forum as nothing goes unseen or "unpunished" (ha). Seriously, I'm glad to have the guidance. Now, I can see with some confidence, I think there are no more real "weak links". Possible upgrades will be gussets for the chassis cross member and solid bushings for the diff. I want to see what it's like with a slight damping effect from the rubber bushings. One more thing might need modification later. I don't know how necessary it is to have the adjustable with spherical rod ended LCAs as some have done with their 3 and 5 links. FFR uses the same LCAs I have for theirs so I'm not convinced there is a need for the higher tech ones but that can be added as well. The added benefit from the change would be a completely adjustable LCA which might help if you want to get your track perfect (some frame variance). I will do a run in the morning to see how the upgrade holds. I will do a little more spirited driving in the AM. The first drive was pretty mild.

WEK.

[Mike N]

What you can do with spherical rod ends on the lower control arms is shim the arms to be less triangulated and more in line with the thrust axis of the car. Having the watts link and highly triangulated lower arms is not ideal. Imagine what would happen if you took the watts link off and pushed the axle sideways as it would be loaded in a turn. The axle would not move perfectly sideways in the car but would rotate, effectively steering the rear of the car. This is not going to produce stable handling characteristics. In my opinion the more you can get the lower arms parallel the better.

[skullandbones]

I'm beginning to feel the effects of the "slippery slope" of suspension work. I was looking at my LCAs after reading your last post (Mike). I was wondering if anyone has taken that FFR adaptor used to create the pickup points for the LCA and the shock (the one mounted on the OEM Mustang mount), done a little surgery on it to move it inboard about two inches? That would allow you to get the LCAs perfectly aligned and also allow you to relocate the shock location. That would give you a little more room for wider tires, too. It looks like it would work with a minimum amount of cutting (some welding required). That sure would be a cool way to get around the problem. I do see what you are referring to regarding the triangulated LCAs. So do you think that the LCAs are creating bind in the system still or is it just the geometry that is not quite right? I am evolving my system as I go so I can still get seat time and move along to the next step without being torn down for weeks.

Thanks,

WEK.

[frankeeski]

WEK, what Gordon does with his setup is what Mike referred to. You stagger the spacers to get the LCA's as close to parallel as possible. You simply can't do that using the FFR LCA's. You will also see better articulation with rod ends on the lowers. If I get out to the garage after work today I will get you a picture of the LCA's on mine.

[myjones]

I was wondering if anyone has taken that FFR adaptor used to create the pickup points for the LCA and the shock (the one mounted on the OEM Mustang mount), done a little surgery on it to move it inboard about two inches? That would allow you to get the LCAs perfectly aligned and also allow you to relocate the shock location. It looks like it would work with a minimum amount of cutting (some welding required). That sure would be a cool way to get around the problem. So do you think that the LCAs are creating bind in the system still or is it just the geometry that is not quite right?
Thanks,
WEK.
SAB
I did surgery on that very part but for different reasons/results. I couldn't stand seeing newly finished cars with the fresh paint rubbed off the inner fender from the coil overs being mounted too close by those torque boxes. I also moved my fuel tank back and down so the frame around that was going to conflict with that shock location anyway. I cut the back of the TQ boxes off and smoothed it out where the shock and panhard bar mounts were, then I made a plate for the inside face of each box that just bolts on. I welded a clevis onto that plate at the height I wanted based on my ride height and the travel range of the QA1's
The top of the shocks are moved inboard to the next hole on the same gusset they used to land on. I also ditched the FF LCA's because they were designed to bind IMO and needed a heim joint in at least one end to work right. Of course once I decided to replace the LCA's I added an inch to center the tire while I was at it. The side plate was key and not that hard to make, when made right it also fixes the coilover binding against the back of the TQ box too. There are pics of my plates etc. in my albums in the gallery but I can take a specific angle if anyone needs it now. I will be installing the fuel tank in the next few days and that is right behind those shocks so it's now or never for more pics. HTH
DB

[myjones]

In my opinion the more you can get the lower arms parallel the better.

I thought he was running the PM3L, so unless he has a panhard bar I missed that advice sounds dangerous. He already removed some of the
triangulation with the change to the UCA's, the shocks are still pretty straight up and IF he moves the LCA's to parallel he has no side to side
control at all for the housing other than the driveshaft hitting the frame. Did I miss something?

DB

[skullandbones]

SAB
I did surgery on that very part but for different reasons/results. I couldn't stand seeing newly finished cars with the fresh paint rubbed off the inner fender from the coil overs being mounted too close by those torque boxes. I also moved my fuel tank back and down so the frame around that was going to conflict with that shock location anyway. I cut the back of the TQ boxes off and smoothed it out where the shock and panhard bar mounts were, then I made a plate for the inside face of each box that just bolts on. I welded a clevis onto that plate at the height I wanted based on my ride height and the travel range of the QA1's
The top of the shocks are moved inboard to the next hole on the same gusset they used to land on. I also ditched the FF LCA's because they were designed to bind IMO and needed a heim joint in at least one end to work right. Of course once I decided to replace the LCA's I added an inch to center the tire while I was at it. The side plate was key and not that hard to make, when made right it also fixes the coilover binding against the back of the TQ box too. There are pics of my plates etc. in my albums in the gallery but I can take a specific angle if anyone needs it now. I will be installing the fuel tank in the next few days and that is right behind those shocks so it's now or never for more pics. HTH
DB

Hey Frank and DB,

I'm not going to turn down good shots of the mod if you can get them. I will be using them for future reference to change the LCA angle if it will work. I'm not surprised that someone has already thought of this but it is nice to have someone doing the "prototype" work and it also cuts down on the R and D for everyone who is contemplating such changes. In the meantime, I will check out your photo gallery (DB).

Thank you guys in advance,

WEK.

[Mike N]

I thought he was running the PM3L, so unless he has a panhard bar I missed that advice sounds dangerous. He already removed some of the
triangulation with the change to the UCA's, the shocks are still pretty straight up and IF he moves the LCA's to parallel he has no side to side
control at all for the housing other than the driveshaft hitting the frame. Did I miss something?

DB

DB, He has a watts link to control the side to side movement. This performs as the equivalent to the FFR 3 link panhard bar.

Bill, It won't create bind if you are using rod ends but it will generate some small jacking forces as the triangulated lower link pair work against the watts link. I haven't noticed anything funky in the handling with my 'almost parallel' lower links. The car does go dead straight when the wheels spin which it never used to.

[myjones]

DB, He has a watts link to control the side to side movement. This performs as the equivalent to the FFR 3 link panhard bar.
Mike
Thanks
I went back and looked at his pics before posting that and I didn't see the watts but I have always learned from your posts so that's why I asked what I missed.
DB

( Quote =Mike N ) Bill, It won't create bind if you are using rod ends but it will generate some small jacking forces as the triangulated lower link pair work against the watts link. I haven't noticed anything funky in the handling with my 'almost parallel' lower links. The car does go dead straight when the wheels spin which it never used to.

All
Keep in mind my pics were before I had all my spacers in. The picture angle hides the Heims but they are all there on the front, so the lowers are double heims
and the uppers are single so the pinion angle adjustments are easy. BTW 1-2* down on mine with Urethane all around. I'll get some finished shots tomorrow but
the shock plates do show up well in the existing shots.
DB
Getting ready for a local show without the body.

[skullandbones]

DB: I didn't see the pics you referred to I don't think. They were 3 pics of a 4 link on a 33 build. Is that it? I wasn't sure if those were the normal mounting points for the shocks either. Also, I didn't see any heims. Do you have a link?

Mike and Frank: I know you guys are experimenting with new shock locations. Is that associated with the FFR bracket that holds the LCA? If you have any pics of your mods, that would be great.

Thanks,

WEK.

[Mike N]

Bill.

On the MkI the upper shock mount bracket stuck through the trunk floor. I made a new bracket that lowered and moved the shock bolt closer to the frame rail with the spring hat below and slightly under the frame rail. The lower mount I also moved but it was so long ago I don't remember why I moved it. Anyway I have never had any interference with the shocks to the frame, wheels, brakes etc since moving them. I don't know if you are aware but to fit 315's on a MkI it took some massaging of the rear 1" tubing and aluminum panels and I moved the shock mounts as a part of doing that. My 315 mod is here http://www.ffcars.com/forums/17-factory-five-roadsters/202067-mki-315-mod.html I also added door bars to stiffen the chassis as shown in this thread http://www.ffcars.com/forums/17-factory-five-roadsters/231660-need-pics-mkiii-door-area-x-roll-bar-plus-additional-roll-bar-you-have-added.html If I have time this weekend I'll see if I can get a couple of photos of my shock mounts.

[frankeeski]

Bill, Here are the pictures I promised.

First is of the drivers side looking towards the back of the car. This is the best picture showing the parallel orientation of the lower control arms.
http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/20140821_220743_zps838959e3.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/20140821_220743_zps838959e3.jpg.html)
The next two are still of the drivers side this time looking towards the front of the car. The first one below it just about straight on and the second from a bit below from center looking up.
http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/20140821_220653_zpsa6b0d726.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/20140821_220653_zpsa6b0d726.jpg.html)
http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/20140821_220628_zps4d4aef9b.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/20140821_220628_zps4d4aef9b.jpg.html)

[frankeeski]

More pictures, this time from the passenger side. First from up front looking to the back.
http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/20140821_220715_zpse5cf00d0.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/20140821_220715_zpse5cf00d0.jpg.html)
Then a couple from the back looking forward. Notice that the spacers are installed to put the LCA's at a position very close to perpendicular with the rear end housing.
http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/20140821_220619_zpse41fb9b2.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/20140821_220619_zpse41fb9b2.jpg.html)
http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/20140821_220605_zps95b71701.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/20140821_220605_zps95b71701.jpg.html)
And I just had to show off a bit of bling. The clear powder coating is really holding up well and keeping the polished aluminum looking new. Look at how the rod ends to the Watts link frame are installed in double shear.

http://i200.photobucket.com/albums/aa78/frankeeski/5-Link/20140821_220641_zpsac8015dd.jpg (http://s200.photobucket.com/user/frankeeski/media/5-Link/20140821_220641_zpsac8015dd.jpg.html)

[myjones]

DB: I didn't see the pics you referred to I don't think. They were 3 pics of a 4 link on a 33 build. Is that it?
WEK.
I should have scrolled back to the (first page) yesterday, I had forgot all about the nice watts you made first on yours.

I looked at the LCA's on mine just now and I'm surprised that no one has just added a longer bolt, angled spacer and put the LCA on the inside face of the TQ box, in other words NOT inside the existing box but outside of it where the longer bolt would project towards the pumpkin. If you do that notice how I made a sleeve for the upper bolts that hold the TQ box to the housing flanges. That sleeved bolt is kind of like boxing the front to help with twisting loads that you would get if you move the LCA outside of the box. Boxing the front would be even safer but might be overkill.

The custom 4 link is in one of my albums and yes it has three pics, I forgot how to drop it in here, sorry
One of those pics is from the front and it shows the sleeve on the top bolt of the TQ box. All of those pics are at full drop on the 4 link so the Link angles all
look bad but I have run it through an online calculator for best launch geometry.
DB

[skullandbones]

Hi DB,

I think I know what you are suggesting about using the LCA "outside of the box" so to speak. As a matter of fact, some of the pics I have on the watts link may show how the rod ends are actually outside of the flange on the two PHB brackets. I just extended the 3/4 inch bolt so the rod end is sitting on it's own perch. It hasn't sheered the bolt off yet. If it does, I will probably have other major issues besides that going on!!! That's what I'm envisioning about the TQ box. If I can move it in about 1 1/2 inches I would get the benefit of the parallel LCA and move the shock lower mount as well. Hope to do a little experimenting with that possibility a little later (next time the roadster is on the lift).

Thanks for all the pics and links. OMG that Gordon Levy setup is pretty heavy duty! I know you are proud of it. The bling is nice. Clear powder coating was a good idea and will probably save more time in cleaning and polishing than the cost of having it done. Those are excellent angles on the TQ box which I need. Also, I see what you and Mike are doing by cheating the angles on the LCAs. That's pretty slick.

Mike: I checked out the links. Those are some wild mods. I'll bet some people would not see what you have done. But it sure would make them wonder how you got those giant tires and wheels under it. It is a bit narrower than the MKIII, right? Pretty cool stuff.

Thanks again for the pics. Now it's time to drive my new 5 link for a while.

WEK.

[skullandbones]

Got back from my "long trip" Sunday at around 1 PM. It was cool most of the trip but when I got back into the Valley of the Sun, it reminded me of why they call it that. It was about 95 and rising. We are having some hot days at the end of the summer season as warm as the middle of the summer. It was still a pleasant time driving through the lower Salt River Recreational Area.

One thing I wanted to verify during my trip was the way the new rear suspension was handling. I couldn't have asked for a better test. There were so many mountain curves that I finally gave up counting or even wondering when they would end. I just went with them. There were several real "hair pins". Haven't seen those in a long time. So there was slow speed turns up to some kind of hairy long down hill (7 degree) ones at speed. I don't think I could have duplicated the seat time I got except on a track. The day to day stuff and terrain just doesn't compare. I was alone some of the time due to some complicated circumstances but with a group of 6 or more other roadsters and a Lotus which was interesting to say the least. Many of the guys have had years of driving their roadster and some are very good and experienced on this particular route. It was hard keeping in the pack. I ended up doing the last couple of hundred miles with one other roadster. We pushed them a little down the mountain. I had new tires and a fresh alignment so I felt like most of the bugs were out of the suspension. With the PS dialed down a little, the steering wheel feel was good but still pretty lively. I had to pay attention at all times with no sight seeing except during stops. Bottomed out a couple of times but I think it may have been wheel rub and not the suspension. The trunk was full. That's another thing. I didn't raise the hood except to show someone the engine a couple of times and didn't do anything else.

I will have to do a close inspection on the lift to see if there was any rubbing or un desirable movement during the trip but all in all it looks good so far.

WEK.