1971viking

I installed the ssbc disc conversion kit and have had nothing but problems.
The car will not stop well and wont lock up the front or rear. I added the ssbc electric vacuum pump since I only had 14psi vacuum. That helped a little but not enough. My rear proportion valve is all the way open. I even tried to close it without any difference.

Next I called SSBC again and they told me to change master cylinder to a 1 inch bore. Better but still not stopping good.

Now they tell me to upgrade my pads to Hawk pads that are $80. Is it worth it? I was thinking of going to a 4-piston setup for $700.

11 inch rotor with 9 inch booster and Master with 1 inch bore. Brake pressure is 1100 which should be plenty.

My wheels are 18x8 but I dont think that should kill my brakes.

Thoughts?

compedgemarine

is the booster a 9 in single or dual diaphram? if single switch to a dual as it will provide a lot more pressure with less input pressure. also which hole is the booter attached to on the pedal?

1971viking

9 inch single. The pedal is not hard so the boost is working.

I move the pedal from the power brake hole to the manual for more leverage.

ScottMHoffman

Has everything been bleed correctly? Master cylinder and brake lines

1971viking

Yes. Tripple checked. No air in the lines.

ScottMHoffman

Did you bed in the pads? Size and weight of the wheels will effect the braking negatively, so both can add to your problem.

Have you checked the temp of the rotors after braking? If the brakes are applying pressure but not stopping I would expect that your rotors would be getting very hot, very quickly. Leading me to believe the brakes are to small. But with your problem I would think you will find that the rotors are not excessively hot which means not enough friction or not enough pressure. Do not know why you would not have enough pressure or what to do to fix it. But if the pads you have are not very good, you will not create sufficient friction to stop. This leads me to agree with SSBC and try a good set of hawk pads. They should include information on proper bed in procedure.

1971viking

A different booster isn't going to make the car stop better, it just lessens the amount of muscle needed to push the pedal down

compedgemarine

not true. I have been thru this a lot with different cars. I build hot rods for a living and have fixed many of them. if you can push the pedal as much as possible and it will not lock up then the booster is not converting the input pressure to enough output pressure. small boosters are fine for light street rods but useless on bigger cars. there is a reason the factory installed 11 inch boosters. when you go down to the 9 inch you need a dual diaghram so that it will output enough pressure into the master cylinder. it is a matter of mass and friction. it takes a lot more friction when you increase the mass.

1971viking

I was told by the SSBC tech that the 9 inch booster is fine for a front disc brake setup with rear drum. I was going to do the dual but they told me unless the pedal is hard that it won't help that much.

I see a good number of people use the dual when they have front and rear disc brakes.

What is the relationship between booster size and vacuum? Is it a constant? Do all boosters need 18-22 vacuum to operate correctly?

compedgemarine

I had a 53 caddy in the shop that came in with a 7" dual diaphram booster on it. they didnt like the way it stopped. the pedal was not hard but and the car stopped ok but you could but the pedal thru the floor and it still would not lock up. talked to the company that had supplied the parts and they said the same, if the pedal is not hard then the booster is enough. I talked with several other brake people who said what I have already said which is the booster is not capable of making enough pressure and said to go up to a 9" dual. made the change and now it will stop on a dime and if you want you can lock it up at will. the caddy has front disc and rear drum. I wont even install a 7" on anything and the only 9" booster we use is dual. some will argue with this but all I can tell you is what I have been thru several times.
hope that helps.

1971viking

Thanks. I will be looking at 9 inches duals.