Rear axle gear ratios

Hi, I recently installed a new (used) rear axle in my manual transmission 93 xj thinking that the newly installed axle gear ratios matched my front 3.07 axle. After I installed and tested it, I found that the ratios did not match. There were two tags on the rear diff I installed, and they read 35 and 0721. What do these mean? the axle I had removed conveniently had a tag that read 307 which was easy enough to figure out. The new axle is a limited slip whereas the old one was an open diff if that makes any difference. any help is appreciated!

as well, until I get this all figured out, would it be best to disconnect the front drive shaft or would simply leaving it in 2 wheel drive be ok?

Two ways to see what you got.

1. dirty method. take diff cover off and look (find) # on the ring gear. Divide smaller number into bigger number. The D35 and 8.25 seem to use the same numbers
43/14=3.07
39/11=3.55
41/11=3.73
41/10 or 37/9=4.10
41/9=4.56

2. less messy way. jack up axle(tires off ground) disconnect d-shaft. turn d-shaft yoke for one tire rotation.
i.e.---
yoke turns 3 times and tire goes around once its a 3.07
yoke turns 3.5 times and tire goes around once its a 3.55.
etc etc with 3.7.'s 4.11's 4.56's

As far as driving that way just DO NOT engage the front and you will be ok. But if it were me just incase I would disconnect you front d-shaft as a safyey measure
Enjoy
Jay

definitely leave it in 2WD until regeared. The best method to find out is to remove the cover and count teeth on ring gear and pinion gear. Divide the teeth on the pinion into the teeth on the ring and that'll be the ratio

Shorty said:

definitely leave it in 2WD until regeared. The best method to find out is to remove the cover and count teeth on ring gear and pinion gear. Divide the teeth on the pinion into the teeth on the ring and that'll be the ratio

Click to expand...

hmmm ok, I'm thinking I will try that since I have to open the diff up again anyways to adjust the depth of the pinion on the ring gear since there is a whine coming out of the rear end as I drive. That is likely the scenario, correct? Is there any way to tell if I need to increase the depth of the pinion or decrease it?

Thanks for both the replies, great info... I'm thinking that the diff in there right now is the 4.10 just judging by how much my speedo was off as I drove. If it works like that...

The whine could be a bad bearing or poor gear mesh. To tell if you need to move the pinion, take a look at the gear wear pattern (or use some pattern paint.) If the pattern is off a bit, you probably will not get good results by adjusting it. Once the gears have worn into each other, that's pretty much how they will run best.

I was wondering if anyone has any info on how to disassemble a positrack diff? The first pin you have to remove is jammed in there quite well, and I'm worried that when I pull it out I won't get it back in and the gears will all slip out of place.

as well, what would a proper wear pattern look like? I'm not sure if the gears are contacting too deep or not...

Thanks for the info