Hey guys, I got a 89 Formula 305 Auto with a rear end that needs to be replaced. I guess it has a 2.72 grear end I think. I wanna get a better one like a 3.42 or something. I have a few prospects at some junk yards too. What rearends will fit the car? I saw a 89 GTA, and two 96 TA's at another junk yard. I heard the 4th gen rear ends fit but are lil wider, which is fine by me I guess, what is wrong with that. Also what units have posi and what so, I'm just trying to get some info on the swap I will have done soon. THanks guys

 

Take a look at the 89 GTA, it might be your best bet.
9-bolt with a 2:77 or 3:27
Limited Slip G80
Alum PBR Calipers & 11.655 discs

 

either 4th gen or 3rd gen rears will fit in your car. 4th gen rears are a direct bolt in but they are 2" wider on each side. If you can look at the rear end and spin it, posi's will spin both wheels in the same direction, non posi's will spin in opposite directions. There should be a number on one of the axles that has the codes for the rear end, or you can mark one side of the rear and count how many times you have to spin the yoke/drive shaft for one spin of the wheel, just an approximate guess at the gears. i.e. 3 1/3 spins is close to 3.23 3.27 closer to 3 1/2 spins would be around 3.42 3 3/4 3.73 and so on. Or just find the make and model of the car it was in and you can usually tell from that. I'd go for a 1990 and up rear end cuz they had 28 spline axles instead of 26 splines on the earlier models. Also, for best performance make sure it's a posi. BTW look at the door codes on the 96 t/a's GU2 is the code for 3.23 gears, if it's a six speed then it more than likely has 3.42's. If it's an auto without the GU2 code on the door then it's probably 2.73's