Residual Valve for Vette 1" master and rear drum brakes?

[pitts64]

I was wondering what size residual valve I should use on my 64 Pontiac?

It has GM D-52 calipers up front with Hawk HPS pads and 11" rear drum brakes..

I'm using a 1" 1972 Vette master, with a 6:1 pedal ratio and the stock 9" booster (9" of vacuum)...

One of these winters, I'm going to start from scratch on a manual system...

[dontlifttoshift]

All drum brakes require a 10lb residual valve, whether it's in the master or a separate valve. It keeps pressure on the lip seal so the wheel cylinders don't draw air.

[Apogee]

As stated above, 10 psi residual pressure valve for drum brakes.

With that low of vacuum levels and the 1" bore master cylinder, is there any reason you haven't just removed the booster from the equation? You're already running the manual 6:1 pedal ratio and 1" MC bore size typically associated with manual installation for the D52/drum applications.

Tobin
KORE3

[pitts64]

Thanks, I'll pick up the 10lb valve...

The booster gives me a little assist but I do plan on removing it.. I thought I would need a master with a smaller bore than 1"..

I once tried disconnecting the vacuum to the booster and drove the car, the brakes were real hard. Would that be caused by the disconnected booster? Or is the a good indicator of what manual brakes will be like?

[Apogee]

...The booster gives me a little assist but I do plan on removing it.. I thought I would need a master with a smaller bore than 1"..

I once tried disconnecting the vacuum to the booster and drove the car, the brakes were real hard. Would that be caused by the disconnected booster? Or is the a good indicator of what manual brakes will be like?

Running with the booster disconnected is similar to running manual, however you have the added resistance of the return spring in the booster as well that you have to overcome, so it's certainly worse. You could swap out your 1" bore MC for a smaller unit, however your pedal travel will increase at the same rate as your output pressure, so approximately 12% per 1/16" bore change. The only other variable you can easily change is the CoF of the brake pads to vary your brake torque outputs.

Tobin
KORE3