i just got a disk brake, posi, 9 bolt rear from a late 80's Trans Am. what is the big difference peformance wise between the 10 bolt and 9 bolt. where are the numbers stamped to figure out what gear ratio it has?

oh and i also got the proportioning valve off the master cylinder, is that all i need or do i need the whole brake booster setup?

 

I think the 9 bolt is a stronger rear end. The haynes manuel says the numbers are stamped on the axle tubes, but we all know how accurate that book is

i am not sure if you need the master cylinder or the booster for the rear discs.

 

Well,
I have the 9 bolt in my camaro and I must say that it is a LOT stronger. You don't need to swap out the prop. valve, if your car came with 4 wheel disks. Now you can reuse the same calipers on your 10 bolt rearend if needed, although you have to make sure that the calipers are either the 82-89? or the 89-92 variety, since they will require different backing plates. If their both from 82-89? then you can just swap rear ends and calipers interchangably.

Steve

 

I had a 9 bolt in my 88 5.7 and have a 10 bolt in my 91. Just wondering why GM would put weaker gears in later cars?

By the way the ratio on my rear end was stamped on the ring gear. It said 13/42 which is the same as 3.23

 

the cost of the 9 bolt was why they just kept the 10 bolt the 9 bolt is an australian rear end.

 

I think its mostly true the 9bolts are a stronger item.

I thought long and hard over it, and decided to switch to a 10bolt.
I can go through 3-4 10bolts for what it would have costed me for gears alone in my 9bolt, not to mention if the posi let go, I snapped an axle, etc.

If anyone wants to argue the point, well I have a 3.27 posi 9-bolt, with PBR discs/calipers + cables for sale.

-- Joe

 

If you weren't clear across the country I'd take that 9 bolt off your hands. It is exactly what I need. BTW, how much are you asking?

 

My 9 bolt had a tag on one of the bolts on the back cover that said the rear end ratio.