So i just helped my buddy do the brakes in his M3 and decided i should look at mine since I havent changed them since i bought the car like 3 years ago. I dont drive the car everyday, but most days when the weather out is nice. According to all the info i got for my 91 maro (including the original window sticker from the factory) i should have rear drums with the 3.08 gears. my rear has disc brakes, sorta small ones, but discs non the less. it also pulls a lot harder than i think 3.08 gears should. anywhos, is there any way to tell if its the stock rear or one out of a diff year (perferably without pulling the cover and drainin the fluid)?

 

yes. turn the drive shaft one turn and see how many turns you get out of the wheel. that is your ratio.
or turn the wheels one full rotation and see how many turns you get on the shaft.
works every time. and its cheap and fast to do to.

someone else posted that as a way, so its not my idea, but it works.

 

Yanking the cover is the best way, but check the following sticky for more info:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

 

well further research shows that i do in fact have the performance package with 4 wheel discs. im gonna yank the diff cover later today and see exactly what gears i got, i feel like changing the fluid anyway. anybody got a good place to get replacement rotors/pads?

 

so i yanked the cover. the ratio stamped on the ring gear says 41:12, which works out to be the 3.42 gears. it also looks like its got the auburn posy, but im not entirely certain. anyone got a definite answer?

 

Yes, that is an Auburn.

 

so any clue why im doing the mighty one wheel burn out?

 

The auburn unit is smoked. You have an RS you say? Disk brakes? Somebody swapped that on. Do you have cast iron calipers rear or PBR aluminum ones? Do your rear wheels stick out about 2" more than the fronts? Count the teeth on your gears. Divide the big number by the small number and that's your ratio.

 

the calipers are the pbr alum ones. the wheels look like they sit the same distance as the fronts, but ive never looked that hard or measured. the stamp on the ring gear identifies it as the 3.42 gears. is it worth trying to fix the posi or no? with it being the 3.42 gears, would that make it a series 3 carrier with 28 spline axles? im the third owner of the car, the first guy bought it new in 90 and used it as his weekend fun car. the second owner used to to go and forth to work. as far as i was told, the car was completely stock when i got it.

 

big gear head wll advise throwing in an Eaton.

JamesC

 

Yes, the Auburn is trash. You can not fix it. The Eaton is the best way to go. Youo will need the Eaton Posi, a set of bearings and shims to set the backlash and bearing preload. That is how I would fix it. The other options are drive it like it is, install a standard differential with a Lock Right, or install a Trutrac. Anyway, stop doing burnouts right now. Dono't keep trying to do burnouts with this worn out Auburn. It will come apart if you keep it up. I have a '96 Impala SS rear end in the shop right now that has a large hole in the top of the housing from an exploded worn out Auburn.

 

thanks for the help. im not gonna bother trying to replace the posi seeing as im in the process of swapping out the entire drive train. ill probably just throw in a 12 bolt and call it good. i might just get a good auburn or something off ebay for cheap though.

 

When you find a good Auburn let me know. I haven't seen one.

 

turns out i dont need one. i swapped the gear oil to royal purple and miraculously im layin down both treads now. i guess they old oil was SO bad that it was preventing the posi from operating. is it normal for diff oil to be slimy green and reak like a dead animal? probably not huh.