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Discussion Starter · #1 ·
Hi all,
Second time I've opened a rear diff and played around. First time I was a little fast and loose.
This is a completely different used unit and I installed a new ring and pinion to 3.73 and replaced all races and bearings. It had one shim on each side that must have been ground to spec and the new kit came with a ton of tiny shims. I mic'd them and started with the largest ones and worked my way down until I couldn't fit anymore in. I spaced it completely even and tried to get a pattern.
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It looked like I needed to move it more in, so I took some shims out of the passenger side and moved them to the driver's side.
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The power side looks a little to the heel and the coast side looks a little to the toe. And both might be too shallow?
Looking for any advise.
Thank you!
 

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I'd say the drive side looks centered pretty well, the coast side is a bit on the toe side. That is not unusual for new gears which I assume you are using. Your pinion depth looks ok and I'll assume you have the crush sleeve torqued in to spec. I think your backlash may be on the loose side, I'd advise adjusting your shim packs and set your backlash at 0.005" to 0.009" if these are new gears. Check at several points and ensure that your backlash readings are all within 0.002" of each other. After setting backlash remember that you need to add shims on each side to establish proper preload. Be sure and take one more gear pattern before buttoning it all up. You might want to get a tube of GM gear marking compound, or equivalent. You can get it just about anywhere, a little easier to read. The tolerances I quoted are from memory so I recommend consulting the service manual to be sure, others here are more knowledgeable than I am so they may have more to offer! In any case, there is nothing mysterious about setting up rear gears, just follow the well documented procedures. Glad to see you are tackling it! Let us know how it works out, and good luck!
 

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Discussion Starter · #3 ·
Thanks, I have .006 backlash as my final reading and the pattern seems the same after tapping in the last shim. I do however have a little play on one half shaft yoke. It looks like the outside of the housing was ground down from the driver's side yoke. When I pulled the old one the spline was ground down so far that the c clip grove was gone. I'm afraid the same will happen again. Do I need a new housing?

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IMO that much play on the half shaft yoke is not going to work. I have heard all kinds of opinions about how much axial play is acceptable. Personally I wouldn't go much over 0.010", and here's why. The design of the C3 rear suspension uses the half shaft as a suspension member as well as an axle shaft. It is the upper link (fixed length) while the lower link is adjustable. The 2 links are what control the camber of the rear wheels.You adjust the camber by changing the position of the lower link. With as much end play as your pictures show, the camber of that wheel is not going to be controlled very well at all. Plus, it's likely to hammer the cross pin and the stub axle end. I'm going to refrain from guessing what the cause might be, I'd have to see and touch it all before recommending something. Some will say that it will be fine just like that, but it won't. It's true that you could put it all together like that and it would probably go down the road just fine, but that excessive end play will be transferred to camber changes on that particular wheel. Something is definitely amiss and I strongly recommend finding the solution. You may have to seek professional help on this one. Keep us posted...
 

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When building a diff you need to get the lash and preload correct, one without the other isn't going to work so to speak.
When dialing in the gears you get to the correct lash,which depends on the mfg. 373 was a US Gear ratio, what brand of gear did you use?

The posi case was previously impacted by the pinion, did you check the posi case for any cracks? The posi looks to be a 69-71. Did you rebuild the posi?

Axle endplay comes from 3 areas typically- posi setup, axle face dimension and in some cases the cross-shaft bore open up a lot.

As you noted that housing was hit by a worn axle in the past and ground down to the seal bore on the RH side. However, the seal looks to be firmly seated in the bore and should be ok. Depending on the axles you installed will depend on if they wear down like the previous ones did. They should have a hardened face, but some new axles are soft. The only way to know is to test them with hardness files or a Wilson Hardness tester.

The white paste shows the coast is high to the toe, while the drive is high center.
 
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