I have a rear end assembly that I got locally. It is supposed to be out of a 1986 Firebird Formula.Did Pontiac make a Formula in 86?
I was told it was a 9 bolt Borg Warner posi unit with cone style clutches. I cannot find much info on this assembly. I only count 8 bolts on the ring gear. If this is a 9 bolt, I should count 9 right? This ratio is 2.7X:1.
Was this typeof rear end used in v8 Firebirds?

 

Many. Also, I do not believe there was a Formula made in 86. Does it have 4 wheel discs? If so, it would be the Borg Warner rear, if not, then it is not. Check out this link, lots of great info:

 

Thanks for the reply. Yes, this rear enddoes have the the backing plates for disc brakes. I did not see your link, could you send it again?
I would like to use this in a 1990 RS camaro with standard differential (305 TBI).Should this be a bolt-in other than changing back plates to keep my drum rear brakes?

 

count the bolts on the diff cover, not on the ring gear. that will give you what you want to know as far as 9 or 10 bolt. the 9 bolt is a stronger unit than the 10.

As far as the disc brake setup, youll need the prop. valve and new e-brake cable, other than that its a direct bolt in.

 

Someone is giving you some incorrect info. No BW 9-bolts used in 1986 on non-existing Formula Firebird. Also they do have (9) gear mounting bolts & and (9) on the cover with a rubber fill plug. The 2:7x ratio also suggest it is a 2:73 ratio which is only used on a 10-bolt,and was on all auto 86 firebirds.

 

Thanks for the replies. This assembly has a rubber plug and cone style clutches. I believe it is the BW assembly (G92?). It is odd that the ratio is 2.73:1 when all the info I can find says the ratios were 3.23, 3.42, or 3.73.
How do the axles come out? Flange bolts and slide hammer? I did not see any accessability to remove any C-rings from within the carrier

 

2:73 is not a BW 9-bolt ratio, the correct BW ones are 2:77,3:08, 3:27 and 3:45. Also RPO G92 is "perfrfomance ratio". The gear ratio is stamped on the OD of the drive gear.

 

thanks, it is a 2.77:1 based on counting the gear teeth. So, to get the axles out of the BW unit, do I remove the 4 flange bolts behind the wheel flange and then use a slide hammer to remove the axle?

 

If you have the 2:77 ratio it is a 1988 -89 and was mated onlyto a 350 TPI. Yes you remove the flange bolts to remove the axle shafts (no "C" clips as on 10-bolt).

 

Thanks. I appreciatethe help.