8.5" vs 8.625" rear ends

http://www.zr2usa.com/mboard/index.php?showtopic=14484

had no idea there was an upgrade from 8.5"

I've noticed quite a lot of confusion about the differences between an 8.5" axle and the 8.625" axle. Especially with concern to the installation of gears or lockers. Hopefully I can address all these issues here.

All ZR2's 94-98 should have an 8.5" rear diff.
Mid year 99 GM switched from the 8.5" axle to the 8.625" axle.
All ZR2's 00-05 should have the 8.625" axle.

That's what it should be, I've heard of a few oddball 8.5's in the later model years.

The only difference between the 8.5" and the 8.6" are the carrier bearings. Anything but the carrier bearings ( carrier, locker, gears, etc ) can be interchanged between the two. The carriers are also slightly different, being that the shaft which the bearings are on, are slightly larger on the 8.625".

I've got a few pics to help illustrate the difference between the two.

NOTE: All of the pics are of my factory gov-loc with the stock bearings. I am not going to take my Detroit out just to take pics, so you'll just have to use some imagination.

*Pay attention to the sizes of the inner diameter and outer diameter of the bearings*

This pic is of the stock 8.5" axle with the stock bearings:
Bearing part #LM501349 Race part #LM501314
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This pic is of the stock 8.625" axle with the stock bearings:
Bearing part #LM603049 Race part #LM603012
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Now if you are installing a carrier or a locker which replaces the carrier such as a Detroit, you may need special bearings. Most lockers that I've seen such as a Detroit, are made for a 8.6" axle.

In this situation, you will need something such as this: ( note the inner diameter of an 8.6 axle but the outer diameter of the 8.5 axle.
Bearing part #LM-102949 Race part #LM-102911
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In some situations, such as if you purchase a locker that does not replace the carrier (such as a lockright) you will have to find an open carrier. If you find an open carrier out of a 8.5" and need to install it in your 8.6" you may run into this situation:
( Note: I do not have the part # for this bearing and race, but your local bearing shop should be able to get it if you give them the dimentions: I.D. 1.625" O.D. 3.0625" width 0.843")
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I recommend that if you are going to order an install kit for gears or a locker, get a kit which does not include the carrier bearings. Once you've pulled the carrier out, check the numbers on the bearings to see which axle you have, then purchase the correct bearings for your application.




I hope that clears up some of the confusion. Any other questions, just ask.

Thanks for the info.
Harbor Freight caliper FTW! I have one at my desk for dirty measurements. Pretty accurate though.