I've found some A grade 3.73 gears from an 04 Silverado for cheap on car-part. What are my junkyard options for a posi unit other than the second gen f-body and a-body cars? The newer the better to make them asier to find. I expect to replace the clutches. If I can't find a used one, what brands should I look at?

What kind of power would I need to have before I need to upgrade from the 28 spline axles on a street car?

 

You didn't say what your'e working on..I'll assume 71 cutlass.
You don't want that governer locking diff from a truck. Stay away from that stuff.
The f bodies are probably 7.5 and you don't want that either.

You'll need an A body posi unit. My limited knowledge tells me you wnat an Eaton style and not an Auburn unit. Both were availabile in GM's of that area. You need an older unit to fit what you got.

28 spline axles are fine on the street. Racing with slicks will eventually break them.

 

After reading even more it looks like I should just get a new one.

 

Last time they used a 28 spline posi in a GM rear was rwd wagon 1987 ish Grand national 1987 (you'll find a lot of those in a junk yard...lol. Being as old as they are and clutches are 200.00 for a set which makes you about 1/2 way to a new unit...
Yep, Shoot a PM will try to help get you a good deal if you like'
rebuild kits
Posi
you already have the gears
Jim
J D Race

 

And just like 60-70s 442s, not all GN rears were ordered with posi - my friend bough a new GN in 1986 and I was surprised it had an open diff. Who woulda thunk it?

 

Right, my junkyards only rarely have anything in the 70s and no Trans-Ams or GNs. The gear I was going to get was from the front of a 4WD, but that won't work. Do you know how new of trucks I could get a 3.73 from? I agree about the posi, I don't think getting a used one that old is a budget move.

 

Many of the 1500 series silverados and suburbans with towing package have good 3.73 gears you can pull cheap, if you want to upgrade to 30 spline bolt in axles retaining original style bearing and seals there are some usable 30 spline Auburn style units in the full size B body caprice, Roadmasters, Impala cars of the mid 90's pretty easy to find. Some are 3.23 in wagons. Find a low mileage car and it can still be in good shape never being abused but if you are spending the dollars on the axles might as well get new better Eaton unit. I miss the old days at Pick n Pull where I could find the 8.5 housing donor, the gears out of another and a posi out of another and build it in the yard and buy just the one rear end for $80