Chassis Hardware

[Bill_VA]

I was thinking about what I should do to my 17-year old car last week, and I came to the conclusion that I might wanna replace all the heim joints on the cars this winter, as they are probably a bit tired and worn out. I hear a bit of clunking going on in the rear of the car when accelerating and decelerating.

This morning I came across a youtube video about chassis hardware. Makes me rethink the crappy hardware that FFR supplies and what I have in my car. This guy is a little rough around the edges, but full of sage advice.

https://www.youtube.com/watch?v=Hj4BifNczCQ&ab_channel=TimMcAmisPerformanceParts

[CraigS]

I have used AN bolts several times but they can have two drawbacks. 1- very expensive, 2- a very tight fit. The shank on, say a 5/8 G5 or G8 bolt is usually .005" to .007" undersize. In 90% of our uses this is close enough. A 5/8 AN will be maybe .002" undersize. In some cases this is important, but it sure makes assembly and disassembly more tedious. I often use G8 bolts (they seem a bit higher quality than G5) and I do follow his advice on having solid shank through all the components. This means I cut off a lot of threaded shank. I find that, if I correctly chamfer the end of the threads a bit, then they start nearly as well as a stock bolt. Using a band sander or grinder I do the chamfer holding the bolt so the grinder is running parallel to the shank and off the end rather than toward the head.
When I want a high quality rodend I go here;
https://secure.chassisshop.com/categories/15342/
Click on chromemoly and scroll to PTFE (Teflon) lined 3 piece style for the highest quality. A 5/8 rodend is $50 but you are getting what you pay for. There are other sources and the keys when searching seem to be chromemoly, 3- piece, PTFE/Teflon lined (PTFE is an industry designation while Teflon is a brand name like Kleenex).

[Bill_VA]

Craig, the rod ends we used on my front LCA conversion were QA1 XMR12 and Summit Racing has those for $30 each (link (https://www.summitracing.com/parts/qa1-xmr12)). The same size rod end on Chassis Shop is $77 (link (https://secure.chassisshop.com/partdetail/AM12-T)). Same dimensions and both PTFE lined. What makes one better than the other?

[F500guy]

I can tell you the Aurora Bearings have a Teflon based cloth type material between the race and the rod, with shields pressed in on both sides to shield the joint. The QA1 have injection molded Teflon insert. Aurora is always more expensive, I have mostly used Aurora in my race car. Not sure that justifies the higher cost, but the race shop I mostly use on-line stocks only aurora and they make aircraft parts, so...With load bearing numbers similar, for street car application it would be mostly personal preference.

[Hoooper]

Look at the car behind him, when he says race car he means it. For pretty much any FFR build what he is talking about is way overkill when it comes to bolt strength selection. How many bolt failures have been reported here?

He seems to have a fundamental misunderstanding of how bolts work. Worrying about the threaded portion of the bolt going through the mounting tab is misplaced worry, if the bolt is wobbling on the tab you already have a problem regardless of whether its threaded or shouldered through the tab. When a bushing with sleeve or rod end is bolted into a bracket the bolt is holding the tab ears tight against the sleeve and movement is prevented through proper tension on the bolt and the resulting friction between the tab and sleeve. The bolt only provides a clamping force so that the friction between the bolted surfaces is high enough to prevent movement. If the force is instead riding on the bolt your joint has already technically failed, it just hasnt broken yet. When a joint is held together in this way the shear force required to overcome the friction between the tab and the sleeve is typically much higher than the actual sheer strength of the bolt.

[CraigS]

Hooper, I agree that an FFR does not need AN bolts. Heck G5 is probably OK. I agree we haven't been seeing any bolt failure reports. I disagree however on relying on friction. If that were acceptable we could use threaded rod and 2 nuts. Having the threaded portion inside one of the mount ears always makes for a loose fit. A looser fit than having solid shank in both ears. Also, I look at threads and see built in bend/break points. I don't want those right where the load is applied to the bolt. I think there is a reason that AN bolts are designed for solid shank in both ears and also a reason they are a tighter fit than G5 or G8 bolts. Maybe an FFR does not absolutely need solid shank in the load area, but it makes me feel better to move at least that far along the gradient from farm tractor to aircraft fastening standards.
Bill, I think F500guy has answered better than I could have. But I will also say that I have used plenty of QA1 stuff as you have. At some point the tradeoff in quality vs cost can get out of hand. I would have a very hard time spending $308 vs $120 just to do your front LCAs.

[rich grsc]

One thing not discussed, is that the holes in the mounts are reamed, not drilled. I too think this is WAY over thought in regards to what is needed for these cars. Nothing we do in these cars reach the limits of structural strength.

[Hoooper]

Hooper, I agree that an FFR does not need AN bolts. Heck G5 is probably OK. I agree we haven't been seeing any bolt failure reports. I disagree however on relying on friction. If that were acceptable we could use threaded rod and 2 nuts. Having the threaded portion inside one of the mount ears always makes for a loose fit. A looser fit than having solid shank in both ears. Also, I look at threads and see built in bend/break points. I don't want those right where the load is applied to the bolt. I think there is a reason that AN bolts are designed for solid shank in both ears and also a reason they are a tighter fit than G5 or G8 bolts. Maybe an FFR does not absolutely need solid shank in the load area, but it makes me feel better to move at least that far along the gradient from farm tractor to aircraft fastening standards.
Bill, I think F500guy has answered better than I could have. But I will also say that I have used plenty of QA1 stuff as you have. At some point the tradeoff in quality vs cost can get out of hand. I would have a very hard time spending $308 vs $120 just to do your front LCAs.

Next time you pull out a bolt check and see how much wear there is in the area that would have been getting abused if the bolt were riding on the mount ears. A threaded rod with nuts on either end, of sufficient grading and torqued high enough to generate the needed friction would certainly also work if you so desired, though it would need to be more expensive than pot metal hardware store threaded rod and definitely not worth the effort vs buying bolts.

Alternatively I am sure a simple google search of how bolts work would turn up plenty of info on the fact that in bushing installations bolts are just the clamping element to generate friction that resists movement between parts.

[CraigS]

Think about these;
- dowels to locate a bell housing to engine block
- engine front covers that often have a sleeve type dowel at 2 of the bolts
- con rod bolts that have solid shank across the mating surfaces of con rod and cap
- main cap bolts similar
- flywheel that has a recess for the crank to fit into as well as 6-8 bolts
- driveshaft flange that has a shoulder to fit into the flange on the diff
- heads have dowels of some type for locating to the block
I think we will have to agree to disagree.

[rich grsc]

Think about these;
- dowels to locate a bell housing to engine block
- engine front covers that often have a sleeve type dowel at 2 of the bolts
- con rod bolts that have solid shank across the mating surfaces of con rod and cap
- main cap bolts similar
- flywheel that has a recess for the crank to fit into as well as 6-8 bolts
- driveshaft flange that has a shoulder to fit into the flange on the diff
- heads have dowels of some type for locating to the block
I think we will have to agree to disagree.
I understand what you're saying, but in every case of your examples, the issue is alignment, or handling rotational force which changes constantly. Thats can't be compared to shock mounts or to suspension components. Just saying:)

[F500guy]

Here you go,
https://www.bing.com/ck/a?!&&p=5de1f44cad0753beJmltdHM9MTY5NDEzMTIwMCZpZ3VpZD0x YWIzMjlmOS04NTEyLTZmNDMtMTA3My0yNjdiODExMjZjZDkmaW 5zaWQ9NTIwNg&ptn=3&hsh=3&fclid=1ab329f9-8512-6f43-1073-267b81126cd9&u=a1aHR0cHM6Ly93d3cuZmFzdGVuYWwuY29tL2NvbnRlbnQvZm Vkcy9wZGYvQXJ0aWNsZSUyMC0lMjBCb2x0ZWQlMjBKb2ludCUy MERlc2lnbi5wZGY&ntb=1

This is what Craig is trying to explain, see page 3! That is why AN bolts have incremental sizing to allow to keep the shank in the shear and not the threads. over kill for a street car probably with proper size fastener, but he is not wrong.

lance

[Hoooper]

Here you go,
https://www.bing.com/ck/a?!&&p=5de1f44cad0753beJmltdHM9MTY5NDEzMTIwMCZpZ3VpZD0x YWIzMjlmOS04NTEyLTZmNDMtMTA3My0yNjdiODExMjZjZDkmaW 5zaWQ9NTIwNg&ptn=3&hsh=3&fclid=1ab329f9-8512-6f43-1073-267b81126cd9&u=a1aHR0cHM6Ly93d3cuZmFzdGVuYWwuY29tL2NvbnRlbnQvZm Vkcy9wZGYvQXJ0aWNsZSUyMC0lMjBCb2x0ZWQlMjBKb2ludCUy MERlc2lnbi5wZGY&ntb=1

This is what Craig is trying to explain, see page 3! That is why AN bolts have incremental sizing to allow to keep the shank in the shear and not the threads. over kill for a street car probably with proper size fastener, but he is not wrong.

lance

Read page 7 of your link. Page 3 states the obvious, the shear strength through the threaded part of the bolt is lower than through the full thickness, obviously that is the case since the cross sectional area is lower. As noted in page 7, its irrelevant when torqued down and relying on friction since the clamping force when torqued down can create a shear resistance much higher than the actual shear rating of the bolt alone.

Believe what you want for written word, or if you cant picture it and are still curious just go pull a suspension arm out and look at how much wear you find. If the bolt is riding on the tab rather than clamping the sleeve tight you will see plenty of wobble between the bolt and the tab, and there will be an area of the tab that the paint is all worn off around where the bushing would be moving around. Compared to how it was new it will be pretty obvious which was happening.

[J R Jones]

There is reference to elasticity and elongation that is achieved at design torque. Some can actually feel this elongation while pulling the fastener to spec. Most of the elongation occurs in the minor diameter of the threads. Shortening the threads alters elongation. Other design tricks are a counterbore/countersink under the fastener head with fully threaded fasteners, The fastener can not elongate where the threads are engaged.
Special applications of long fasteners like head bolts require unique fasteners with reduced shank diameter to achieve elongation at spec clamp load. The elongation spring load optimizes clamp load over time and thermal cycles.
On rod ends: They do not have shock damping like synthetic bushings. Well plastic liners have a little, mostly the soft liner keeps dirt out of the joint. The non forgiving nature of rod ends causes NVH through the chassis and challenges fastener clamp loads. Urethane bushings are a great compromise. Measuring displacement of synthetic bushings would show that is actually very small in new parts.
jim

[F500guy]

Read page 7 of your link. Page 3 states the obvious, the shear strength through the threaded part of the bolt is lower than through the full thickness, obviously that is the case since the cross sectional area is lower. As noted in page 7, its irrelevant when torqued down and relying on friction since the clamping force when torqued down can create a shear resistance much higher than the actual shear rating of the bolt alone.

Believe what you want for written word, or if you cant picture it and are still curious just go pull a suspension arm out and look at how much wear you find. If the bolt is riding on the tab rather than clamping the sleeve tight you will see plenty of wobble between the bolt and the tab, and there will be an area of the tab that the paint is all worn off around where the bushing would be moving around. Compared to how it was new it will be pretty obvious which was happening.

Read page 7,
"Other types of shear joints rely on initial clamp load to resist slip. This type of joint requires a frictional
force between the joint members. The shear forces have to overcome the friction developed by the
clamp load, which in most cases will be far more than the actual “shear strength” of the fastener itself.
This type of joint is common in the structural steel construction industry and may be referred to as a
friction-type or slip-critical joint."

Hope my suspension is mostly friction less, but I would need to sharpen my calculator to get the force of .063 metal sleeve clamped at 100 ft/lbs. I will try google first.

[Nigel Allen]

I am really enjoying all the mechanical engineering conversations and content on this thread. I guess the other factor to take into consideration is the shear strength of the human body. Pretty sure most of us would be strained through the harness before any bolts sheared.

Not all that pleasant to think about.

[Hoooper]

Read page 7,
"Other types of shear joints rely on initial clamp load to resist slip. This type of joint requires a frictional
force between the joint members. The shear forces have to overcome the friction developed by the
clamp load, which in most cases will be far more than the actual “shear strength” of the fastener itself.
This type of joint is common in the structural steel construction industry and may be referred to as a
friction-type or slip-critical joint."

Hope my suspension is mostly friction less, but I would need to sharpen my calculator to get the force of .063 metal sleeve clamped at 100 ft/lbs. I will try google first.

I sure hope your bushing sleeves are thicker than 0.063 and aren't frictionless between the end of the sleeve and the tab! Yikes!

For a 1/2" sleeve at 0.125" wall and 100 lb ft dry bolt torque, fairly low 0.3 coefficient of friction the force required to slide the sleeve would be 13,100 lbf. In this case with a bushing in double shear it's 26,200 lbf. On that same 1/2" bolt if it's grade 5, fine thread the bolt would be expected to shear at about 12,300lbf (bolts aren't rated for shear, far as I can see 60% of minimum tensile strength is the rough number). Let me know if you come up with different numbers, I think the calculations for static sleeve are pretty straightforward but I could have missed something

[F500guy]

Way above my meager knowledge at this point, thanks for increasing and opening the thought process. I looked at this formula listed below and got different numbers, as well as different shear numbers for grade 5 bolt. So, I will end my contribution to the conversation on 1 final note:

The bolt can be empirically measured, but the friction, clamping force and perfect alignment of a joint can be subject to field imperfections so the calculated value could vary from ideal, always good to have a safety margin.

F=T/K∗D
where F is the clamping force, T is the torque applied to the bolt, and D is the diameter of the bolt.

[CraigS]

This is certainly interesting. Thanks for the contributions guys.