OK I bought my 91 RS and was told that it had a 4th gen rearend in it and that it was from a 01 SS. It still has drum brakes but is a posi for sure. I know the car came with a 3.08 open rear and this is supposed to be a 3.42 posi. I suspect that this is right because i changed my speedo gears because of the speedometer being off and now it is correct. I am planning on putting ZO6 wheels on it and was wanting to be reassured that this WAS a 4th gen rear. Also is there any special way to tell for sure.
THANKS

 

It's definitely not a rear out of an '01 SS if it's got drum brakes. Maybe a pre 98 v6 rear though. The 4th gens didn't come with 3.08's. Autos had either 2.73 and SS's had 3.23, and the M6 cars had 3.42.

 

well i never said that the 4th gen had a 3.08 but im for 99.9 % positive that this rearend is a 3.42 but thats not what matters. Is there a way to tell what this came out of

 

What wheels are on the car could tell us if you have a 4th gen rear or not. If you have stock 3rd gen 15" wheels, the wheels will be even with or sticking out of the fender wells. As far as I know, all 98+ F-body's had disc rears, 93-97 V6 Cars had drum rears, usually with an open rear.

 

If it has drums it's not out of a SS car.

If it's a 4th gen rear with drums, it came out of a 6-cyl car; and I'd guess the odds are less than 1% that it came with posi. Which of course doesn't mean that it doesn't have posi now, only that it didn't come with it.

The only way to know for sure what gears it has, and whether it's posi or not, is to take off the cover and look. All else is speculation and monkey-spank. If you haven't looked, you don't know, period.

A 4th gen rear is nearly 2" longer on each side, than a 3rd gen rear. A 3rd gen rear is about 61" from axle flange to axle flange; a 4th gen is about 3½" - 4" longer than that, but I don't recall the exact dimension.

Sounds to me like you've been fed the usual used-car salesman pack of lies. Time to forget all taht stupidity and take off the cover and look, if it really makes any difference to you. But since you just bought the car, and as you well know the very first thing you will be doing with a car you just bought is to change the fluids, you'll be taking the cover off next weekend if you didn't already do it this weekend; so maybe you've already looked. If not, then you'll have the chance as soon as you do the proper maintenance. Let us know what you see when you do.

 

Why couldn't it be a rear from an SS and have drum brakes? Not everyone sells their rear with brakes... Drums will bolt on.

 

ok well first off i bought this car last year around christmas when i was 16... So myabe i did get get taken advantage of but i dont think i did. I haven't pulled the rear cover off as i haven't even put 2000 miles on the car this year. So far I've had my hands tied with building the motor for this car and getting it running let alone working everyday of the week so i can pay for it. The wheels are the stock 91-92 16" and they dont stick out much like i think they should with a 4th gen rear. The edge of the rim is even with the inner lip of the QP... Could i tell what year it's from by the casting numbers on the rearend????

 

Here is how a stock 16" wheel looks with a 98 Rear,