I've been looking for either a 3.42 or a 3.73 posi that'll drop into my 91 Z28 vert but I'm finding that I'll either have to pay $400 bucks for one local or drive to the dfw area and hope that I don't waste a day. Are there any other vehicles that are viable donors without a bunch of mods?

 

80s & 90s S10/S15 used the same ring & pinion size as the thirdgens. The posi carrier in those trucks isn't very strong however. It is a locking type posi unit that tends to break under hard use. The gearsets however will hold up same a third/fourthgen gearset. I'm currently running 3.73 gears from an S10 in my camaro, but I have a posi unit from a fourthgen. You could also try looking at the impalas/caprices from the 90s as well as the 80s Monte Carlos, I'm not sure what rear axle they used, but it might work.

 

Are you talking about a complete rear end or just a set of gears and a differential? If you want a complete bolt in rear end the only true bolt in will be from a '82 to '92 Camaro or Firebird. The '93 to '02 Camaro and Firebird rear ends will bolt in, but they are about 4 inches wider.

If you want a set of gears and a differential then the S10 is going to be your best bet because the other cars that used the 7.5 rear end usually had 2.73, 2.56 or 2.41 gears in them. The Governor Lock differential that was used in the S10 isn't very good for a performance car and should be avoided. A new Yukon Dura Grip or Eaton Truetrac would be a good choice. Be sure to match it to the axles that you have. The '82 to '89 rear ends had 26 spline axles and the '90 and later rear ends had 28 spline axles.

 

Ideally I would like a complete rear end including discs.

 

For a complete rear end your only options is third and 4th gen F body cars.

Like BGH said, all 82-92 camaro/firebird will swap right in, and the 93-02 camaro/firebird will bolt right up but are wider and will force you to run 4th gen wheels on the rear to make it work

 

That's kinda what I figured since I hadn't seen anyone else reference any other donors but i thought I'd ask. Guess I'll just be patient and keep looking.

The 4th gen wheels are a no go for me. I wouldn't mind a little wider spacing in the rear but not at the expense of the original wheels. Thanks to all for responding!

 

be aware that most v6 third gens had 3.42 gears and they are the same as the v8s other than the ratio.unlikely to be posi though.

 

Only 4.3L S-10s had the 7.625" ring gears in '88-'93, all the rest were 7.50". This matters, as the R&P are the weakest link, once you have 28-spline shafts. And 4.3s could have 3.42:1, same as in the Astro minivans.
Setting up gears isn't bad if you're patient, so I'd get S-10 gears and a '98-'02 Zexel Torsen takeout. Genuine GM 3.73:1 7.625" gears are scarce, but finally appeared in some later 2.2L S-10s. Likewise 4.10:1. Most GM 3.73:1 are 7.50". Or from a big pickup = useless to us.

 

I've been doing a little research and it looks like the 3rd and 4th gens have the same 5x4.75 bolt pattern. Why wouldn't my stock 3rd gen 16's work?

 

Wrong offset, the tires would stick out from under the fenders. Someone else already noted the '93-up axles are wider.

 

#$&* I'm having a helluva time finding a donor without driving a couple hundred miles.

 

Pretty sure that all 7.5 rear ends were upgraded to 7.6 in or around '86.

 

Yes same bolt pattern. In fact all small/mid size GM rwd is same 5 x 4.75" pattern. S10, monte carlo, camaro, firebird, nova, etc.

It's the backspacing/offset. Flip the wheel upside down and measure from the back of lug mounting pad to outside lip.

The 4th gen wheels are around 2.25" deeper.

This is the same reason why you need 2" to 2.25" thick wheel spacers on third gens when you put 4th gens on them.