which master cylinder do i need for installing a 79-81 trans am rear end with rear disc brakes in a 68 firebird, at the local auto parts store they told me that the 79 and 80 master cylinders are the same but the 81 is different, which one do i need?

thanks

For power brakes?

yes power brakes, sorry about that

I think in 81 GM started using the aluminum quick-take-up type master cyl with plastic reservoir. The calipers had a different seal design that retracts the pistons a little extra for lower drag and better fuel economy. The QTU master cyl has a third larger piston at the rear to pump more fluid at first, then the other regular pistons take over. There is a special valve in the rear reservoir port that holds back fluid from venting to the reservoir until a high pressure is achieved in the rear "extra" piston. This valve makes bleeding the system more difficult because the rear of the MC takes a long time to refill.
This Master cyl is a good one to use for higher pedal, but worse in that it can take longer to bleed the rear brakes. When bleeding the rear, wait a minute or so for the bore to refill before depressing the pedal again and you should be OK.

I think you can use either one, but the newer one will have a higher pedal. If your front brakes are not the late model type then you can probably use either one.

I just remembered something else.
The quick take up master cyl also has a larger OD rear boss around the large rear piston. If you have an older style booster for an iron master cyl, it won't accept the later master.
David

the front brakes are from a 69camaro.
i'll probly get the 79/80 master because its cheaper. right now i have a booster for a 69camaro, so should get the a booster to match master cylinder i get? or will the 69 work? i'm not really sure about that graemlins/clonk.gif

I'd use the 69 booster if you have one, plus the 69 master cyl should be the same bore size (1 1/8") as the 79 master, and will have the same functioning, probably line size too. The 79 master probably has a square reservoir shape instead of rounded one which is more correct for a 69.

There are two different lengths of pushrods coming out of the booster that press on the master cyl, a long and a short. There are two depths of master cyls, a deep and a shallow. Don't mix them or the master cyl won't work.
David

right now i have a 69camaro master cylinder for power brakes and i can't get a hard pedal.
it was mentioned to me that i should be using the master from a trans am with 4-wheel disc brakes, but now that you mentioned that it would be the same size and function, i'm really confused now :confused:

here is my other post, just to let you know the problem

http://www.camaros.net/forum/ultimatebb.php?ubb=get_topic;f=7;t=006355#000000

what should i do?? :confused: :confused: :confused:

[ 04-20-2004, 03:08 PM: Message edited by: kilo_00 ]

I have basically the same set up as you on my Nova. I can tell you that the adjustment on the rear brakes is very critical. There are many links on how to adjust them. Mine work great, have a high, hard pedal, and are consistant. I am using a Master Power 9" booster and M/C, along with the T/A prop valve. When I stop, this car will put me through the windshield!

Tim