make sure you get a correct size and axle for your jimmy

ZR2 axle will NOT FIT into 4x4 or 2wd spring because of ZR2 spring bracket location is different.
also front diff too have to swap front control arms and etc too much headaches...

easier job is put in a correct size axle.
also get from blazers and JIMMY

look at glovebox to get the RPO CODES

BLAZERS/JIMMY never offers DRUM rear brakes.

2001 Jimmy axles offers
4x2, 8-1/2" ring gear (3.42 ratio, GU6)
4x4, ZR2 opt (3.73 ratio GT4)
4x4, w/o ZR2 opt; 7-5/8" ring gear, 3.42 axle ratio (opt GU6)
4x4, w/o ZR2 opt; 7-5/8" ring gear, 3.73 ratio (opt GT4)
4x4, w/o ZR2 opt; 8-1/2" ring gear (3.42 ratio, GU6)
4x2, 7-5/8" ring gear (3.42 ratio, GU6)


Also i added a picture to tell you which ring gear you have.

i OWNED 6 different blazers 88,92,93,98,98,00

Whew, getting two different stories here... I am not intending on doing the ZR2 axle.

That said, Jamaroon and blazerguy, you are both saying slightly different things.

I have a 7 5/8 ring gear rear end 4x4. I am also certain it will be a 3.42 (I will check the glove box code). If I go with a 8 1/2 ring gear 3.42 ratio, will that still be a suitable replacement?

You are 100% wrong on this. There have been lots of people that have swapped in the ZR2 rear end.


The front diffs are exactly the same regardless of if it was a ZR2 or not. Gear ratios are the only variable (other than if it was a bravada front diff, then it had the one piece shaft) ZR2's have longer CV shafts but the control arms are the same lengths.


Spreading wrong information is useless and confusing for others, if you don't know what you're talking about then don't say anything.

Yes, that would be a good replacement, but it will be fairly hard to find. Not many came with that option.

I used to think that also until I measured them all at 38.5 inches pin to pin

you don't want to go through this again im big on pull-a-part but I would suggest a bearing kit and ring and pinion unless you enjoy this kind of work. Just my O-pinion Motive Gear GM10BI-30 Differential Rebuild Kit | Auto Parts Warehouse

My ring gear says 11:41, so it turns out it's a 3.73 G80. Guess I am going for a zr2 or the same stock one. Interestingly enough, the ring gear I swear looks to be stamped 7 7/8. You can see it on the videos I posted. Either way, I would hate to go back to a 3.42, but if I have to I'll pull a 3.42 front as well. I could do that at a different time so long as I DO NOT use 4x4, correct? Sometimes the fronts are taken out of these cars already.

Thanks for all the help guys. I went to pick-a-part today and first blazer I looked at had a GT4 G80 7.65" in the back. Pulled the cover and the diff was clean with minimal metal on the magnet. Locker was working great. What's more is they were having their half off parts sale and today was the last day. Wow!

Took 2 hours to pull and loaded it up in my old 1970 Ford F250 truck. Went to AutoZone and picked up a new 7.65" gasket and some 75w90 (IIRC) for LSD or open diff. Once home I pulled the old diff in a little less than two hours. Took 2.5 hours to clean and install the "new" axle. Another hour for bleeding the brakes and cleanup. All in all not too bad. Pretty quick and fun little project. Drove the Jimmy and drives perfectly smooth. The reverse clunk is 95% gone (new U-joints would prolly help). No clinks or pops around corners.

Really lucked out on this project over and over guys. Going to be sore tomorrow doing it all by myself, but my wife can finally drive her car again and I feel fortunate providence shone in my favor. Next up is the complete front suspension kit I got. Have a new ball joint puller set I am itching to test out. :)

Glad you got it fixed

Thanks for the information in this thread. I just blew out my rear end and this thread has so much information. Thanks guys.