Im wanting to put a 4th generation rear end in my 91 Firebird. I know that it will bolt right in and will be wider. But i was wondering what gears they came with, and are all of the 4th gen rear ends posi. I plan on pulling it out of a car in a junkyard, but i wanna make sure i get the right year, and whether i should pull it out of a v6 or v8 depending on what gear i want. any info would be appreciated.

 

Alot of v6s came with open 3.08s in the auto, not sure about the manual(maybe 3.23), but they were all open. All v8s came with lsd, some had 2.73s and some had 3.42s.

 

so all the v8 4th gens do have lsd? is there anyway to tell what gear is in it...like by year or anything. obviouslt it would be different for auto and manual. i want a 3.42 but i want it to be in already. but more importantly i want to limited slip

 

Just look for a ls1 with m6. It will have posi and 3.42s. Also, if they tranny is missing, look for the door codes on the drivers side door. I think it should have gu6 for 3.42s and g80 for lsd. Not positive, do a search on a v8 board for that, but its the easiest way to tell if you think the rear was left stock.

 

and some LT1 cars had 3.23.

 

Call your local GM parts dept. and give them the last 8 digits of the vin# and they can tell you exactly what it has, providing its the original rear.

 

My knowledge of the 4th gen rears is as follows:
93 6 speed - 2.73
94-02 6 speed 3.42
V6 cars - 3.08
LT/LS A4 cars without "1" on shifter plate - 2.73
LT/LS A4 cars with "1" on shifter plate - 3.23

This makes it easy when looking through salvage yard cars.
Hope this helps.

 

so are all fourth gen rear ends lsd?

thanx

 

Same as with any other rear end - only way to know 100% for sure is to pull the diff cover off and look - the gear ratis will be stamped in the ring/pinion, and you'll be able to verify the lsd upon sight.