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Single or dual diaphragm?


Supporting Member
Supporting Member
My little bucket will eventually have disc brakes front and rear. The front will likely be one of Speedway's GM metric setups (unless I can find something lighter). The rear is going to be a weird setup...A Ford Mustang/T-Bird setup, with drilled and slotted rotors and performance pads.

I'm trying to spec out going with power brakes. I've run across conflicting recommendations for the type of booster to use...single or dual diaphragm. I've found recommendations for single boosters for cars under 3000-3500 pounds. Mine should be around half that. But I've also found recommendations for dual boosters for disc/disc systems. I've found no recommendations for cars that are both lightweight and have disc/disc setups.

As always advice is always welcome.
Bill, if you are committed to the hand controls, in my opinion, the more mechanical advantage you can get, the better. The trade off would be possible over sensitive brakes, but with a adjustable proportion ing valve and some pre designed lever adjustability via a bell crank or just different holes at various positions on the lever could be dialed in, or out, depending on perspective. The more power assist, the less mechanical force will be required to stop, so that would allow shorter hand control and less effort. Also smaller brakes would seem bigger. I don't think there is much difference in size between them, I've seen them advertised in 7" diameter. As an example, I own two ford trucks, one is a dump, one is a roll back. Both have basically the same brakes, Diesel engines, etc. the dump has a vacuum pump and power brakes, the roll back is heavier, has the same engine, vacuum pump, etc, but also has hydro assist. There is no comparison as to stopping power. The roll back will put you through the glass if you arent easy on the brakes. The dump stops fine, just no where near as intense. I am not in any way an expert, just my thoughts.
I wish it were a matter of choice, but hand controls are going to be a must. I'm now to the point of not being able to drive without them...and I'm getting worse fast. If my deterioration keeps up at the rate of the last week and a half, I'll not be able to stand at all by next week.

I don't see me doing much custom fab work for the hand controls beyond mounting brackets, since there will be no such thing as off the shelf brackets. The only other scenario for custom fabbed hand controls would be if I decide to roll the dice and take a chance of adapting some of the cruder controls to work with an extension off the top of my originally planned manual system pedal. If it didn't work, chances are I'd never drive the car.

I'd not thought of the potential for extreme oversensitivity. I was looking to save some $$ and a few crucial inches if I could stick with the single.
I have a single diaphragm booster on a T-bucket with drum rears and disc. fronts, although the disc. front brakes are Wilwood 175's on spindle mount motorcycle wheels, meaning that they don't do a whole lot. The car weighs 2000 lbs. and will stop if you just "think" brakes. I really didn't need the booster at all. I realize I'm comparing apples to oranges to here if you are going to use hand controls, but what I have is very sensitive and the pedal is very easy to push to the max.

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