So i managed to find a steal at the junk u yard. I found a Trans Am with Rear Disc and Posi. The rear end is by b/w but i cant seem to find the tag anyway in my firebird manual. Is there something im missing?

 

I don't quite understand. Does the rear end have the tag on it? The Borg Warner rer end had a tag bolted to the cover instead of having numbers stamped into the axle tube. The tag gives all of the rear end information, such as gear ratio. These rear ends were only offered with a 2.77 or a 3.27 gear. There are rumors of a 3.45 gear, but I haven't seen one. There are 3.70 and 3.73 gears available for it, but as far as I know there are no other gears for this rear end.

 

thanks for that im hopin for the 3.70 gears....it has an aftermarket cover on it so there was no way of knowing

 

sure there is, take the cover off and count the teeth on the gears.

little to no real chance of those gears being in there. Most likely a 3:27

 

aw yea is there like a formula of do i just count teeth

 

Count the teeth on the ring gear. Count the teeth on the pinion. Divide one by the other.

36 teeth on the ring gear. 11 teeth on the pinion. 36/11 = 3.27

There may also be 36/11 or 36-11 stamped on the side of the ring gear. If it's a 2.77 diff, it's not worth getting. That uses a 2 series carrier and the only gear set available is 2.77.

The 3.70 gears were never offered in a production car. You'll either find 2.77, 3.27 or 3.45

 

ok with out going under the car maybe i could get a clue at what im looking at its a 84 trans am 305 ho a/t tranny with aluminam drums im hoping for 373s what do u think may be in it

 

Aluminum drums? I don't think a GM car has come with aluminum drums since the 60's.

A 1985 TA HO with a 305 and A/T had two gear options. 3.42 and if it has the G92 RPO code, 3.73. In the last 25 years, it could have had anything put into it.

 

Some Camaros, at least, were equipped with alum drums (RPO J42). I believe they're discontinued, but I see them for sale occasionally.

JamesC

 

my car when i bought it had alum. drums on it and on counting the gears w/o taking the cover off mark the axle or tire if there is one on it and spin the tire once completely and count how many times the yoke spins it will give you a GENERAL idea of what's in the rearend 1 tire rotation 3 1/4 yoke turns =3.27 we do it at the shop unless we need to know for sure what's in it

 

Make it easy on yourself just look for the Mfg's gear ratio stamp on the gear OD. BW 9-bolt ratios are 2:77 & 3:27 for Automatics and 3:45 for the manual.
Forget about a 3:70 very few and are long gone from salvage yards.

 

You sure it was a 9-bolt? I've seen the aluminum drums on a 10-bolt. My 94 Z28 had aluminum drums on a 3.73 posi 10-bolt.