I have a 92 RS, and the PO has swapped the rear axle after the car was rear ended. Problem is, I believe from the factory the car was equipped with a 2:73 open differential with drum brakes. The axle equipped on my car also uses drum brakes, but i notice it is a limited slip diff. Whoever installed the axle sucks. The gear ratio is different, cant be 2:73s. Installer did not change the speedometer gears to correct specs, so when im cruising down the road the speedometer is quite inaccurate. For example if i am travelling 65 mph the speedo indicates 80 mph. I work at a auto repair place so i pulled the car onto a lift and called the chevy dealer with some numbers I found on the bottom of the pumpkin. They could not identify. All i can tell is that its a 10 bolt posi drum brake with low gears, PO couldnt identify gear ratio. I have yet to pop the cover off. I am looking for any insight in identifying this axle, and more importantly the gear ratio. I was told it was pulled from a third gen, but im not even sure of that, could be fourth. Is it even possible to identify gear ratio by popping off the cover? sounds too good to be true. On top of all that, I was cruising in my camaro today and the speedo dropped, it doesnt even function... So id like to do a few things, if possible.
1- identify axle and gear ratio
2-service axle(ill need to do a bit of research on this note)
3- find out problem with speedo, fix it and make it read accurately(no clue on this one)
ive done searches on identifying rear axles, and they all say to use the vin # well this is swapped so i cant quite do that.
If anyone can offer any info regarding any of this id really appreciate it.
thanks

 

First step is to go get a new diff cover gasket and 2 quarts of 75w90, should be $15 for all of it. Then get under there and pop the cover. After all the old lube has drained, you'll find numbers stamped into the perimeter of the ring gear. You may need to jack one wheel up and shift to neutral to read all the numbers. Then you can know the ratio and make it easier to correct the speedometer. Reinstall the cover, unthread the fill plug, squeeze lube in until it dribbles out the bottom of the hole. Snug the plug and check the stickies here for speedometer info.

 

Check the 10-FAQ sticky at the top of the page for info.

JamesC

 

Must not be much of an auto repair place if someone there doesn't know how to service the rear end and tell what the gear ratio is.

All GM gears are marked with the number of teeth on the ring gear and the number of teeth on the pinion gear. If you can't find the numbers, or don't understand what they mean then count the teeth yourself. Divide the number on the ring gear by the number on the pinion gear and that is the gear ratio. If the ring gear has 41 teeth and the pinion has 11 teeth then the ratio is 41/11=3.73

 

Yeah its a paint shop, but point taken. thanks for the info everyone.

 

there is another way that doesn't involve taking the cover off, even tho that's the best way and the oil probably needs to be changed, anyways: use the GPS and a dpeedometer app in your smartphone to find out what rpm it runs at in the 1:1 gear (3rd on an auto, 4th on a stick) at 60mph...

since the speedo is calibrated for 1000 rpm's at 60mph, you just move the decimal over a couple of places, and that's your final drive ratio...
example: if you come up with 2300rpm at 60, then that means that your final drive ratio is 2.3:1 (2300/1000) and you need a speedo drive and driven gear combo where the driven gear has 2.3 times as many teeth as the drive gear...