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Discussion Starter · #1 ·
I know at the end of the day it's the pattern that matters...

But, need some other eyes on this math. I have a new Truetrac with a new R&P. No markings on the factory pinion, so it has the factory shim at about .0975 or so.

Standard pinion depth: 2.547
Motive pinion depth marking: 2.551
Difference: +.004

That, I think, means that I subtract .004 from the standard pinion shim size.

If I do so, there's no way I can set the pinion preload. I'm using the Ratech shims and not a crush sleeve, but even if I put on a new crush sleeve, there's a ton of play and no way I can set the preload even with a crush sleeve. If I add more shims to the inner bearing to pull the pinion in, I can get the preload set, but that just seems wrong. Those shims should be for depth/backlash.

So, I got it setup with a good pattern, but with the pinion where it's set, that gave me a pretty thick set of shims on the right, and a pretty thin set on the left (ring side). Given the factory shims were the same left to right, it all just seems odd. Now I know there are machining tolerances that are different between what Eaton did and what Hank at American Motors did (probably on a Friday), but would you just say "Shims be damned, it's all about the pattern"?

-DO
 

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Yes, in the end its the pattern that matters. Even if using setup gauges, the final verification is a pattern check. Make sure the back lash and preloads are within spec.
 

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I did R&P work on a friends YJ several years ago and at final setup, there was only one thin shim on the driver's side carrier bearing but the pattern, preload and backlash were good and they ran quiet. Cheap gears not machined to factory tolerances but they worked.
 

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Discussion Starter · #4 ·
OK. That makes me feel better. The FSM instructions allude to somewhat of a balance of shims left and right.

I wouldn't say that I had an awesome time setting this all up... :)

Can't wait to tackle the TF-999 rebuild...

-DO
 

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OK. That makes me feel better. The FSM instructions allude to somewhat of a balance of shims left and right.

I wouldn't say that I had an awesome time setting this all up... :)

Can't wait to tackle the TF-999 rebuild...

-DO
Regardless of what the manual says, the diff carrier shims have to be positioned to give correct backlash and preload. Differentials that have the carrier shims located between the bearing cups and housing are easier to setup than Dana 30, 44, 60 with the shims located under the bearing cones.
 

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Discussion Starter · #7 ·
Yes, AMC 20.

Everything seems fine, including the pattern. Just wanted to make sure having the shims very different from factory wasn't raising any red flags.

I used the FSM process of determining what the starting shim set should be by measuring the back and forth of the unshimmed carrier. Then worked my way into a proper backlash. Bit of a pain once you get things set and one side has about 8-10 shims and the other has 2. Those thin ones are easy to bend, so I sandwich them between the thicker ones.

-DO
 
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