4th gen rear end why???????
 

I bought a 92 Z28 and thought it had the stock rear end in the car. So I bought another rear end that was a 410 posi to go into my car. I found out someone switched it with a 4th gen. Why would they have done that the stock rear end had disc brakes and I posi. Is the 4th gen a better rear end or something please help thanks.

Are you sure it's a 4th gen rear? The 3rd gen and 4th gen rears are pretty much the same.

pictures please.

Yes I'm sure it's a 4th gen a friend of mine is I 3rd gen freak and he seen it and told me it was a 4th gen. And ad for pics I don't know how to post pics on here not real good with a computer sorry.

Very likely your car needed a new rearend, and the previous owner used a more plentiful 4th gen rear as a replacement.

the 4th gen rear ends (depending which one you got) the M6 rear end has a 3.42 gear (pretty much perfect if your car is a TPI) and a better differential then the 3rd gen.. the 4th gen rrat is also like 2" wider then the 3rd gen rear

It's not much better. It's still a GM 7.5" and they are not strong. They do not handle much abuse, especially from manual trans cars. But you are right on the widths being different. OP, your wheels would stick out past the fender well if you had a fourth gen wheel with 3rd gen back spacing. I would know. I have 3rd gen wheels on my 4th gen.

1th gen rears are the same 3rd Gen 10-bolt except for the following.

4" wider overall length (2" per side).
all are 28 spline axle shafts.
Limited slip is auburn (weak) & SLP torsen (stronger?).
Stock ratios are the same 2:73, 3:23 & 3:42
Also come as open diff.
Brakes...Drum & Discs.

Nothing special about the 4th Gen rears except more can be found now.

I have a chance to pick up a 4gen. posi rear end from a 2000 fire bird. From what I have read in this form the only difference would be that it is 2 inches wider per side. This one has the torson posi and disk brakes and comes with the 28 spline axels. I am guessing that the gen 3 axels are 26 spline. So other then a new off set rim it should bolt in and be a upgrade to the stock 3gen rear end.

All 10 bolt, 7.5 GM rear ends are 28 spline. Doesn't matter if it was in a third gen, fourth gen, S10, Blazer, etc. They are all the same with exception of widths, mounts and the F body rears have the provision for a torque arm. Otherwise, the internals are the same. Spline count, u-joints, yokes, seals, bearings, crush sleeve, gears,....you get the point.

If you use a fourth gen rear end, you need to use 4th gen backspacing to keep the tires tucked like factory.