TKO transmission shim

[boat737]

After following the threads, I knew I would have to shim up the transmission. (427w, TKO, Moser M9). It seemed that most people were good with a 3/4 inch shim, some with 1 inch, so I decided to start with the 3/4 inch. Got it all made up and painted and installed it. Eyeballing it, it looked real good. I, once again, used EdwardB's ideas on the design of the shim. Thanks again Paul.

I then searched the forums on drive line alignment and started working on that. With the 3/4 inch shim, and adjusting the 3rd link, I could just get within limits of the pinion angle of 1 degree, and operating driveshaft angles of 1.6 and 2.6 degrees, again within limits. But of course my OCD couldn't leave it alone. I figured I could get it better.

When I bought the 3/4 inch stock from McMaster, I also ordered 7/8" and 1" stock as well, just in case. So I made another shim from the 7/8" bar, painted it, and installed it. This got me just about perfect. Another small adjustment on the 3rd link got me to a perfect 0 degree pinion angle, and operating angles of 1.5 on each end of the drive shaft. About as good as you can get.

Of course, with all the measuring and figuring, I came across another little issue. My rear axle was a little cockeyed, which meant that the car would not track perfectly. It wasn't off by much, but, ah heck, I noticed it and now I had to fix it. The FFR lower control arms are not adjustable, so I ordered Gordon Levy's adjustable lower control arms and installed them as well. By measuring off the frame, I adjusted the rear axle straight(er). Only about 3/8", but it should be real close now.

The bottom line: the rear end and drive line should all be perfect now.

[edwardb]

Glad my shim fabrication ideas were useful. Looks like you're getting things dialed in. Two comments. First, you don't mention ride height. I assume this measuring and adjusting you're doing is at ride height? Otherwise it's not valid. I suspect you've got this covered, but just double checking. Second, for your three link, you actually want a little negative pinion angle at rest. The pinion will rise some under load. I believe most recommend 1 to 1-1/2 degrees negative for this suspension. Then under load it is around that zero degree ideal number.

[boat737]

Good points, Paul. I was laying in bed last night and remembered that I should have noted the ride height in my post.

Yes, I have the ride height set at 3.9" front, and 4.25" rear. Once the car is finished and at final weight, I'll re-adjust the ride heights back to those numbers.

As for the pinion angle, I thought about that, but figured I would tweak the 3rd link, or the LCA's later, once I was closer to final weights and such. As for the 1 to 1-1/2 figure, I was thinking less than that. Am I wrong? I'll need to go back and research some more I guess. I was figuring less than 1 degree, like maybe 1/2 degree, especially now since I have no rubber bushings in the rear axle set up at all. The LCA's and the 3rd link all have Heim joints now, so would that eliminate, or nearly so, the movement under load?

It's amazing how you change one little thing on the drive line, and it affects 3 or 4 other things. Go figure.

[edwardb]

Good points, Paul. I was laying in bed last night and remembered that I should have noted the ride height in my post.

Yes, I have the ride height set at 3.9" front, and 4.25" rear. Once the car is finished and at final weight, I'll re-adjust the ride heights back to those numbers.

As for the pinion angle, I thought about that, but figured I would tweak the 3rd link, or the LCA's later, once I was closer to final weights and such. As for the 1 to 1-1/2 figure, I was thinking less than that. Am I wrong? I'll need to go back and research some more I guess. I was figuring less than 1 degree, like maybe 1/2 degree, especially now since I have no rubber bushings in the rear axle set up at all. The LCA's and the 3rd link all have Heim joints now, so would that eliminate, or nearly so, the movement under load?

It's amazing how you change one little thing on the drive line, and it affects 3 or 4 other things. Go figure.

You're thinking through this and all good. I personally don't have any 3-link experience, so can't give you a firm answer. Only what I've seen from others. It's going to move some as the suspension moves and squats under acceleration for example. I can't say whether 1/2 degree or whatever is right. Only that zero at rest may not be quite right. But you know how to adjust, so easy enough to tweak. The only diffs that don't move are the IRS ones that are bolted to the frame. Doesn't apply to us, but some rear suspension types, like leaf springs, they put the pinion angle at negative 5 or 6. Those are obviously really moving!

[boat737]

You're thinking through this and all good. I personally don't have any 3-link experience, so can't give you a firm answer. Only what I've seen from others. It's going to move some as the suspension moves and squats under acceleration for example. I can't say whether 1/2 degree or whatever is right. Only that zero at rest may not be quite right. But you know now to adjust, so easy enough to tweak. The only diffs that don't move are the IRS ones that are bolted to the frame. Doesn't apply to us, but some rear suspension types, like leaf springs, they put the pinion angle at negative 5 or 6. Those are obviously really moving!

Thanks again. Maybe I'll start a new thread to see what the consensus is on what an "un-loaded" vs. "loaded" pinion angle should be.