I just completed a manual swap into my firebird, and the stock 2.7 rear end gear is way too high for the poor t5, so I would like to purchase a limited slip rear end with a 3.43 gearing. However, after ordering several wrong parts during my transmission swap, I lost my confidence, and would like to be 100% sure the rear end will fit before I buy it. My question is, how do I identify my current rear end, so as to get the correct one? My Firebird is an '89 coupe, and that is the year they changed over so I know I can't just listen to people who say "Ohh you have an '89 that is an X size by 28 spline rear end". So how do I definintively tell?


-- Henry

 

On your year the only way is to count the splines.

 

You could look at the stamp on the rearend housing, usually on one of the axels, then give us the code to translate. Or if you are lucky, the tag on the diff. cover will still be there. Counting the splines is a PITA, but you just might have to.

If you are trying to figure out the Gear Ratio by itself, then you could jack the rear off of the ground (be careful), and see how many times the driveshaft turns to one rotation of a wheel. This will give you a ball park figure, but it works for seeing the difference between 2.77's and 3.23's and so on. Or last but not least, if you have to break open the rear end, divide the number of teeth on the ring gear by the number of teeth on the pinion gear, this will give an exact number. Also there is a stamp on the outer edge of the ring gear that will tell you what the ratio is. The stamp will read something like this: 11:41, 41 divided by 11=3.73.

I think thats about it. Hope this helps.

 

I'll make this one easy.

Call around to a few different wrecking yards, tell them you want a 3.42 or 3.73 posi rear for a 82-92 F-body. It's really that easy.

You don't need to worry about splines or if you have a 9 bolt or a 10 bolt since you want to buy a whole rear and not the parts to build yours into one. Don't be suprised if you have a hard time finding a 3.42 posi , 3.42 is a V-6 ratio so it's not real common to find a base engine with posi. You should consider 3.73's also, they made my T-5 livable and aren't really that bad on the highway.

 

Have you checked the RPO codes on your console lid??

P.s.
I could sell ya mine!!! But I wont...