What is the consensus for a pinion angle on a 3 link

[boat737]

I recently posted a progress report on my shimming of the TKO transmission ( http://thefactoryfiveforum.com/showthread.php?23171-TKO-transmission-shim ). EdwardB brought up a good point on properly setting up a pinion angle in a static (unloaded) condition, versus the loaded pinion angle that is desired. Right now, I'm at a 0 degree pinion angle, static, and was going to tweak it to a slight negative angle in order to have a 0 degree angle under load. I have a Moser M9 rear end, a 427w, TKO600, custom 11-1/2 inch driveshaft with Spicer 1350NZ U-joints, and with Gordon Levy's LCA's on the 3 link setup. All pivot joints on the 3 link have Heim joints, so there are no rubber bushings in the suspension, and I hope very little angular deflections and rotating of the rear end and pinion.

With that, should there be minimal negative static pinion angle (I'm thinking in the neighborhood of a half degree), or does it need to be more pronounced, like 1 or 2 degrees, (or more)? Apparently, the really "loose" rear ends (leaf springs, etc.) need way more that that, but I'm hoping my setup is solid enough to need a very minimal negative pinion angle (static).

What say all of you?

[Jeff Kleiner]

With poly bushings I set the front of the pinion 2 degrees down relative to the trans output shaft. Yes, it would stand to reason that there would be less deflection at the diff with the solid heims. Haven't ever dealt with a heim jointed rear so I can't give you a definitive number but one thing that I would keep in mind is that unless the transmission is solid mounted even though the rear end may not deflect under load the trans will effectively changing the angle between the output and pinion.

Jeff

[GoDadGo]

Here's a U-Joint Phasing Video that may help you decide where it needs to be.

https://youtu.be/gmV4qwLfOMY

[boat737]

With poly bushings I set the front of the pinion 2 degrees down relative to the trans output shaft. Yes, it would stand to reason that there would be less deflection at the diff with the solid heims. Haven't ever dealt with a heim jointed rear so I can't give you a definitive number but one thing that I would keep in mind is that unless the transmission is solid mounted even though the rear end may not deflect under load the trans will effectively changing the angle between the output and pinion.

Jeff

I have the standard Energy Suspensions trans (and engine) mount. Will the trans move (vertically I assume) that much to affect the pinion angle and/or operating angles? Thanks Jeff.

[NAZ]

You'll likely get several opinions on this subject but remember you're trying to achieve a pinion angle that matches the trans output shaft angle under load (acceleration). Unless you have a way to measure the change in pinion angle from static to under load you're just guessing. On three link or parallel four link systems with heim joints and equal length control arms I set the pinion angle the same as the the angle on the trans output shaft. Since heim joints don't give like bushings, there is no appreciable rotation on the axle with heim joints and since the links are equal length there is no change in pinion angle in bump or rebound (until you adjust the anti-squat to the more extreme positions). If you run a shorter UCA your pinion angle will change as your axle moves up and down. In this case you want to set the static pinion angle so that under acceleration the pinion angle matches the output shaft angle. This will change as you adjust the anti-squat. So on these short UCA systems you need to know the change in ride height under acceleration to determine the change in pinion angle from static to under acceleration. This requires testing.

[boat737]

You'll likely get several opinions on this subject but remember you're trying to achieve a pinion angle that matches the trans output shaft angle under load (acceleration). Unless you have a way to measure the change in pinion angle from static to under load you're just guessing. On three link or parallel four link systems with heim joints and equal length control arms I set the pinion angle the same as the the angle on the trans output shaft. Since heim joints don't give like bushings, there is no appreciable rotation on the axle with heim joints and since the links are equal length there is no change in pinion angle in bump or rebound (until you adjust the anti-squat to the more extreme positions). If you run a shorter UCA your pinion angle will change as your axle moves up and down. In this case you want to set the static pinion angle so that under acceleration the pinion angle matches the output shaft angle. This will change as you adjust the anti-squat. So on these short UCA systems you need to know the change in ride height under acceleration to determine the change in pinion angle from static to under acceleration. This requires testing.

Thanks NAZ. Sounds like a lot more measuring, calculating, figuring and thinking in my future. This will be a street only car, so I don't expect I will be applying all 500 hp every time I come out of a turn or leave a stop light (although I am still 16 years old in my head, so you never know.) That said, would there be a huge difference under "accelerating" load (say, 0 to 60 in a tire blistering 0.3 nano seconds, or you get the idea), verses a "non-accelerating" load (a steady speed, at say, 40 or 50 mph)? i.e. there is still a load at a constant speed and no acceleration, just a lot less load I would imagine, eh?

Also, if I do have a shorter UCA (I don't know yet, I haven't measured it or the LCA's, and won't be able to for another week or two) wouldn't that aid in counteracting the downward angular tendency of acceleration (I measure the angles from front to rear on all the components) with an upward angular rotation during bump (and that be a good thing)? And if the UCA was by chance longer, that would exacerbate the downward angular tendency?

[NAZ]

I would suggest that first you determine if your lower and upper control arms are the same length -- if so, simply set your static pinion angle the same as the output shaft. If you have a shorter UCA you can measure the pinion angle gain or loss from ride height to 1" bump by backing off your coil overs until the ride height is 1" lower at the rear (best to measure this as close to the wheel center-line as practical-- but always in the same location for repeat-ability). If the change is relatively small (say 1/4-degree) you can choose to ignore it or adjust the static pinion angle by this amount in the appropriate direction. This is a starting point. These light little cars with stiff springs shouldn't squat much more than an 1" unless you have lots of power and sticky tires.

[CraigS]

The UCA is definitely shorter than the LCAs. OTOH, set it at 1 -1.5 deg and forget about it. If you watch that video you can see the problem but it is visible only at higher angles. I am convinced from my 3 link over 9 yrs driving that 1-2-3 deg is not noticeable.

[boat737]

Thank you all. I'm off to another week of school, in Miami this time. So no work on the car for a while. Keep those comments and ideas coming.

[Mike N]

I would suggest that first you determine if your lower and upper control arms are the same length -- if so, simply set your static pinion angle the same as the output shaft. If you have a shorter UCA you can measure the pinion angle gain or loss from ride height to 1" bump by backing off your coil overs until the ride height is 1" lower at the rear (best to measure this as close to the wheel center-line as practical-- but always in the same location for repeat-ability). If the change is relatively small (say 1/4-degree) you can choose to ignore it or adjust the static pinion angle by this amount in the appropriate direction. This is a starting point. These light little cars with stiff springs shouldn't squat much more than an 1" unless you have lots of power and sticky tires.

I have a 3 (5) link set up with rod ends at all joints and set the pinion angle to zero (same as trans) with the rear under about 1" compression. Never noticed any vibration and the car hooks great. The FFR 3 link upper and lower links are not dramatically different in length so the pinion angle really doesn't change much with suspension travel. Someone at go kart stage could easily measure the pinion angle change with a digital level, tape measure and a floor jack.

[BEAR-AvHistory]

(although I am still 16 years old in my head, so you never know.)

Think most of us are afflicted with that infirmity. I did 2* based on the recommendations of the guys here who understand suspensions better than me. 7,000 miles later still good to go.

[rich grsc]

Holy Cow, talk about over thinking something. Ask your Dr. for some meds.:rolleyes:

[boat737]

Holy Cow, talk about over thinking something. Ask your Dr. for some meds.:rolleyes:

Hmmm... Check out my first thread. I have already pronounced, freely and proudly, that, "If it's worth doing, it's worth over doing." And concerning the meds, the doc's won't give me anymore.

[mikeinatlanta]

While we are overthinking it...
How will you spend most of your time, and when are you most likely to feel a vibration? Most time is under light load and cruising the highway. Same for time most likely to feel vibration.

How will actual suspension load change pinion angle? Basically, does the moving suspension change your pinion angle, and if so, how much load will you normally carry and at what ride height?

Or... For a rubber bushed rear, just set it about 1 degree (from output shaft) down at ride height and rock on. When setting final ride height, make sure and do it with anticipated load in the car.

[NAZ]

Boat 737, the easiest way to determine how much the pinion angle changes with movement of the rear axel is by backing off your coil overs and measuring the pinion angle while jacking up your chassis (or put the chassis on jack stands if you prefer to jack the axel). You can check from full droop to full bump and chart it every inch. This gives you a handy chart of the change per inch of travel. Once you have the car at the go cart stage, the easiest way to determine how much actual squat under acceleration is by installing o-rings on the shock shafts and setting them against the shock seal area. Launch the car hard on asphalt where you can get good traction and the o-rings will act as a tattle tail showing how far the shocks moved in bump. That's the axel location you want the pinion angle to match the trans output shaft. The reason you want the pinion angle set at that point is because under load is where you get the worst vibration. Now that may be over the top for some folks but to racers and engineers this is just another few hours of testing to ensure your set-up is on the money. Or you could just use the "by guess and by golly" method and never look back. Obviously some folks have guessed at the angle and are happy with the results even with a variety of different settings. With this method you don't have to guess at a setting or copy what someone else has done because you don't know how to arrive at the correct setting yourself.

[boat737]

Thanks again NAZ. I see you've done this before. I'm in the go-kart stage now, so all this is certainly doable for sure. I'm also in the Calif. registration process, so I am going to have to temporarily get the body on so I can get my brakes, lights, CHP, VIN inspections done (next month), but I think I can at a minimum get some of your measurements accomplished. I do like the idea of having some numbers of my own to do my set-ups. Once I'm back in town, I'll get on it and post a follow up. Good info, thanks.

[boat737]

Here's some update.

I managed to do a rear suspension "swing" from full extend (droop, rebound), to a compressed (squat) position of about 3 inches travel. I couldn't compress the shocks completely because I couldn't back off the coil-over adjuster ring all the way. The ring was hitting the mount on the axle, so without removing the struts/shocks, I could only go so far on the adjustment. Bottom line, I got measurements at 4 spots, 1 inch apart. And got some good info.

The upper link is roughly 16 1/2 inches long, and the lower control arms are about 17 1/2 inches long. So they are close, but not the same. One set of dimensions I couldn't really measure is the distance, vertically, from the forward mounts/pivots on the 3rd link to the LCA's, nor the rear mounts/pivots, hence, I don't know if the LCA's and the third link are parallel to themselves as the rear axle travels up and down. (Like a parallelogram).

My starting pinion angle, at ride height, was 1.3 degrees absolute down (all my angles are measured from front to rear), which is the same as my trans output shaft. What I learned is that the more the shocks extended and the axle dropped away from the frame, the more downward angle (absolute) the pinion went, and conversely, the more the shocks compressed, and the car squatted (axle moving upward), the less downward angle the pinion moved. The range of angle was 3.0 degree absolute down at full extend, to 1.0 absolute down at partially compressed/squatted, or about .6 degree per inch of travel. The way I figure it, that is a good thing, because as the car would squat, as in a hard acceleration, the more the pinion angle would increase (again, measuring angle from front to rear), and fight the tendency to have the axle housing (aka pinion angle) rotate and add to the downward angle.

So, now for the static angle. I had adjusted the pinion angle equal to my trans output shaft angle at 1.3 degree down, or more correctly, my pinion angle and trans output shaft angle were the same, making the pinion angle 0 compared to the trans output. The operating angles on the driveshaft were about 1.5 degree on each end, well within the accepted limit of 3 degrees. It appears that a some of the people with a 3 link like a 1 to 2 degrees pinion (to trans output) angle to account for a pinion angle change under load or acceleration. I'm thinking a bit less than that due to the heim joints in my LCA's and 3rd link. I'm thinking there is less movement and rotation with the Heim joints compared to the standard rubber bushings in the FFR LCA's.

So today I tweaked the 3rd link and raised my pinion angle about .6 degrees, from 1.3 down to .7 down. The trans output of course stays the same at 1.3 degrees down. Now the pinion angle to the trans output is .6 degree. The operating angles on the driveshaft are still in the 1 degree or less range, so that's a good thing. I don't know for certain if this is enough, but I figure that with this .6 degree starting angle, plus the additional .6 degree with a 1 inch squat, I'm looking at a 1.2 degree pinion angle to the trans output under strong acceleration/load, which in theory, will try to zero itself out under the strong load.

If any of you are still awake after all this, here is what I've put together. I have a 7/8 inch transmission mount spacer, with a static .6 degree pinion/trans output angle. With a 1 inch squat under hard acceleration, the pinion/trans output angle should increase to 1.2 degrees. Now, does any of this make sense?

Oh, and I made a few tools to help me out. I made 4 bolts that I adjusted to 3.9 inches (2 of 'em) and the other 2 at 4.25 inches. I just stand them up under the four corners of the 4 inch frame tubes and adjust the coil-overs to just have the frame touching them. The other tools I used to measure my rear axle "swing" for my above measurements. I bolted a 3/4 inch socket to a yard stick, and hung it on the upper shock bolt. As I raised and lowered the axle, the scale would tell me how much I was moving the axle.

[NAZ]

If I'm following this it appears that the pinion angle and the trans output shaft angle will be within .1-deg at 1" of rear squat which is close enough. You can check your actual squat once you get it on the road by using the o-ring on the shaft trick. I leave the o-rings on the shafts as I use them for more than determining the squat on a hard launch. But if you don't want to disassemble the shocks you can use a wire tie instead of the o-ring and cut it off when your done. Now, what are you using for the ride height where you set your static pinion angle? And how did you arrive at that height? This will be another one of those subjects that there are lots of opinions on. I'll give you something to consider when establishing ride height. To eliminate roll steer you want to run your LCAs level (parallel with the ground). If the pivot points are higher or lower at the front than the rear pivots the rear axle will skew when the car rolls in a turn. This will cause the car to yaw and the rear axle to provide steering input. Since the FFR frame has no provision for adjusting the LCA pivot points up or down to get the LCAs level you need to adjust your ride height. So if you don't want roll steer your LCAs will dictate the ride height.

[CraigS]

Don't the brackets that are bolted to the bottom of the axle have two holes in them for the LCA anymore?

[boat737]

Don't the brackets that are bolted to the bottom of the axle have two holes in them for the LCA anymore?

I just looked. They do. My LCA's are in the bottom holes, which makes the LCA's angle downward from front to rear about 3 or 3 1/2 degrees. Not quite parallel to the ground like NAZ suggested. I went with the bottom hole thinking it would yield a lower force or torque on that LCA pivot bolt. Being farther from the center of the axle I figured it would give a bit more stability to the axle housing. I think I can live with that, being this will be a street car, eh?

[Jeff Kleiner]

Upper holes for cornering, lower holes for straight line hook up. Take your choice.

Jeff