More brake holding power

[Rick Unterseh]

Need Help Guys !!!!! I'm trying to build more brake holding power on the starting line. I've got the factory GM discs in the front and drum in the rear of my 2nd gen. Firebird, removed the power brakes, added bigger wheel cylinders and went to a GM truck master cylinder with disc/drum application. What are you guys using out there.... tired of pushing thru the lights.

[Sean Marconette]

What are you using for a proportioning valve? That might be the place to look.

Sean

[Billy Nees]

Rick, what you may want to look at is late 60s early 70s Olds Vista Cruisers. As I recall they had 3"x 9.5" rear drums and shoes instead of the 2x9.5"s on your "bird. You will probably need backing plates and all but there should be a way to make them fit!
Sean, GM cars don't have proportioning valves. They bias the brakes with MC bore size and WC size.

[njk53]

Rick, we had an issue similar to yours but in the burn out box. The line lock would not hold the car in the water. We went around in circles trying to figure our what was going on. As it turned out, there wasn't enough heat in the brake pads to hold the car. Before you go to the starting line work the brakes to get some heat in them to see if that helps. What kind of brake pad are you using? We went to a Hawk brand and it helped a little but, I still have to work the brake to put heat in the pads.

Also, I am not sure which GM vehicles Billy Nees was referring to but, we have a 71 Chevelle wagon that has the stock proportioning valve on it.

Also, an adjustable proportioning valve may help by putting more bias to the front brakes. The discs have better holding power than the drums.

[cad]

I'm disc/drum also.

At what RPM are you trying to stage? Are you using a 2 step?
What are the converter specs?

I can stage at 3000 with a 2 step on my ATI TreeMaster, but can only footbrake about 2600 before it slides the tires on mine.
My converter is a true footbrake 4600 flash converter.

Clark

[Jim Whitehead]

Rick, You need to move the pivot on the brake pedal up to make the pedal longer (more Leverage) also get two sets of rear brake shoes and only use the biger shoes primary on front and rear side. also an adjustable pro valve.

[MikeFicacci]

When I had discs up front and drums in the back of the 'Vette, I was having trouble holding it on the starting line. Like Jim said, I moved the brake rod up approximately an inch and it allowed me another 150-200 pounds of brake pressure. Just be careful any time you mess with the brake rod.

[Tom Goldman]

Originally Posted by Jim Whitehead

Rick, You need to move the pivot on the brake pedal up to make the pedal longer (more Leverage) also get two sets of rear brake shoes and only use the biger shoes primary on front and rear side. also an adjustable pro valve.

Right on the money.
Move the pivot for the push rod approx. 1 1/2" higher on the pedal . ....you may need to put on a adapter on the mount to locate the master cyl higher to keep the pushrod straight..
This will increase the pedal ratio to around 6-6 1/2 to 1 and allow higher pressure without higher effort.
Stock powerbrake pedals are only about 4-1 ratio........Adj prop valve is for biasing initial pressure front to rear and has little effect on holding on the line.

[Jim Cimarolli]

I have seen 11 x 2 rear brakes for mid 70's intermediate cars. Stands to reason that if you can keep the rear wheels from moving,,,,

[Billy Nees]

Originally Posted by njk53

Also, I am not sure which GM vehicles Billy Nees was referring to but, we have a 71 Chevelle wagon that has the stock proportioning valve on it.

The valve you are speaking of isn't a proportioning valve. It is a check valve that shuts off pressure to the front or rear brakes in case of a fluid leak.