[67 455 Bird ragtop]

What is a good minimum vacuum for a power brake booster??? With the cam I will be running I think I'll have a vacuum problem there. I'll know once I fire up the motor in a cpl of months. Also, are there any smaller style boosters that don't need a lot of vacuum. I'll have 4 wheel single disc brakes on my 67 Bird. If vacuum is low are manual 4 wheel disc brakes a viable alternative??

[ September 11, 2002, 04:29 PM: Message edited by: 67 455 Bird ragtop ]

[67 455 Bird ragtop]

What is a good minimum vacuum for a power brake booster??? With the cam I will be running I think I'll have a vacuum problem there. I'll know once I fire up the motor in a cpl of months. Also, are there any smaller style boosters that don't need a lot of vacuum. I'll have 4 wheel single disc brakes on my 67 Bird. If vacuum is low are manual 4 wheel disc brakes a viable alternative??

[ September 11, 2002, 04:29 PM: Message edited by: 67 455 Bird ragtop ]

[Big Injun]

We have 4-wheel disc brakes from Stainless Steel Brakes on our GeeTO TIGER. You really need a good 18 inches of vacuum. We are running a small booster and a big cam on the Tiger and it was only good for one stop so we went with a electrical vacuum pump from SSBC. It now works great!

[Dave A]

Minimum vacuum needed depends on a lot of things, including how you intend to drive it. A single stop at the end of the quarter mile is easier to handle than trying to negitiate a road course or intense stop and go traffic.

The more brake output you have, the less vacuum you'll need. When you run out of power assist, you'll still get additional braking by pushing harder (until you bottom the master cylinder out), it'll basically be like manual brakes for any braking beyond running out of assist you do.

I have a basically stock disc/drum system on a '71 T-37; it does fine with about 11" idle vacuum and about 18" cruise vacuum.

Smaller boosters offer less assist than larger boosters in general since assist is proportionate to diaphragm area. Tandem boosters can be used to increase diaphragm area but still clear engine components. There are some cases where power assist is dependant on how much booster vacuum you can 'trap' in a short period of time (i.e quick WOT to hard braking transitions), in which case a smaller booster, which is 'charged' more quickly, may provide more assist.

[Brian Baker]

It all depends on the size and efficiency of the booster. The power brakes on my '79 T/A have worked fine with as little as 10" of vacuum at idle. Late 70's GM's have the smaller booster, I believe your 'bird has the larger one, which will not work very well with lower vacuum readings.

I would wait and see exactly how it works, and if it functions poorly, look for a smaller one out of a later model car. I have also heard that the 9" boosters that were available on Pinto station wagons are a direct bolt-on for our GM cars (but I've never tried one) and they work great with lower vacuum producing "big cam" engines.

[Big Injun]

Hey Brian, where you going to find a Pinto station wagon???