Anyone know the size of the rear ends of our cars? I just got a 1991 RS camaro, and its not a posi. it has rear drums. ratio is a 2.73. im getting a posi unti from a 1994 T/A with 3.43 gears. will it fit my car with any problems? need help ASAP.
2.73 is series 2, 3.42 is series 3, short answer is no.
The 94's gears won't fit on the 91's carrier but if you swap carrier and gears, it will fit. They're both 7-5/8" diffs. They'll also both use 28 spline axles but the 94's will be 2" longer.
Supreme Member
The way I understand it is that he's getting the posi unit, carrier, and gears, which is the way I got my 3.42s out of a 4th gen (not installed yet though).
Basically, it will fit right in no problems. Use your stock rear, use your stock axles (since its a 91 it has the same 28spline ends as teh 4th gens), and install the new unit/gears.
The other option (if the 94 is close to your place and doesnt need to roll), just swap the entire rear end into your car, especially if you think you'll want to upgrade to 4th gen wheels in the future. That way you don't have to deal with setting the gears up.
Basically, it will fit right in no problems. Use your stock rear, use your stock axles (since its a 91 it has the same 28spline ends as teh 4th gens), and install the new unit/gears.
The other option (if the 94 is close to your place and doesnt need to roll), just swap the entire rear end into your car, especially if you think you'll want to upgrade to 4th gen wheels in the future. That way you don't have to deal with setting the gears up.
all it is, is the differential. no carrier, no axles. i was gonna use my stock axles and carrier as long as it would fit into my 1991 carrier. picture is not the posi i am getting, but an example
A posi/open/locker etc is the carrier. That's the part that holds the ring gear and has the side gears for the axles etc.
The 94 carrier will fit in your 91 and your axles will fit but you'll also need the 3 series gears. Since you're going to use the 94's 3.43 then there's no problem.
If all you're getting is the 94's housing then you have a problem. As I already mentioned, fourth gen axles are longer so you can't use third gen axles in a fourth gen housing. Other than that, the diff is a simple swap sharing mostly everything except the axles.
GM started using 28 spline axles in 90 for the third gens so your axles are the same as a fourth gens except for length.
Your first post says you're getting a posi with gears from a 94. Your last post says you're getting a fourth gen housing and you want to use your carrier, gears and axles So what is it?.
The 94 carrier will fit in your 91 and your axles will fit but you'll also need the 3 series gears. Since you're going to use the 94's 3.43 then there's no problem.
If all you're getting is the 94's housing then you have a problem. As I already mentioned, fourth gen axles are longer so you can't use third gen axles in a fourth gen housing. Other than that, the diff is a simple swap sharing mostly everything except the axles.
GM started using 28 spline axles in 90 for the third gens so your axles are the same as a fourth gens except for length.
Your first post says you're getting a posi with gears from a 94. Your last post says you're getting a fourth gen housing and you want to use your carrier, gears and axles So what is it?.
How I read it is you only have the carrier, you will need a set of series three gears to use with your stock axles and housing. Its all about interpretation (feeling like I am supreme court justice.)
well its the carrier, and the 3.43 gears. im gonna use my axles
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Its a 3.42 gear 
By the way, how long til you get this installed? I'd like to get an idea of how it feels going from 2.73s to 3.42s. I know others have done it and liked it as well, but I'd like to hear another opinion. I have a set of 3.42s in my garage with the 3-series posi carrier waiting to go into my car.
By the way, how long til you get this installed? I'd like to get an idea of how it feels going from 2.73s to 3.42s. I know others have done it and liked it as well, but I'd like to hear another opinion. I have a set of 3.42s in my garage with the 3-series posi carrier waiting to go into my car.