Technical Brake System Issues.

I have a 1934 ford coupe. It has Chevell / El Camino front brake calipers. The rear brakes are Currie 11 inch drum system. I am using a 7 inch single diaphram power booster and a dual 1 inch master cylinder. The system was power bled three times. Upon trying to stop the car the brake pedal goes almost to the floor and the brakes do not lock up. I recently swapped out a leaky master cylinder and power booster. The pedal ratio is 4 to one. Brakes were fine for the last ten years. I have swapped out the recent booster and master cylinder twice, no change. I have .020 clearance between the booster and master cylinder . HELP!

 

What is different from when the brakes worked good for the last 10 years? Is the master cylinder the same bore as the one that worked?

 

The master cylinder is the same bore.The original master cylinder looked like a GM type but the outlet line holes were opposite of normal, pointing to the chassis. The cylinder I am now using has outlet ports on both sides.

 

Are you using check valves to prevent the fluid syphoning back into the under floor M/C?

 

Is 4:1 pedal ratio enough for power assisted brakes?

 

Did you bench bleed the master cylinder

 

I am using check valves,2 lb to front, 10 lb to the rear .

 

4 to 1 pedal ratio is for power brakes , 6 to 1 is for manual brakes.

 

I bench bled the master cylinders before installing them.

 

Pedal going to the floor. So the pedal obviously moves, it's not a hard pedal/no brakes problem. If it goes to the floor, the fluid must be getting pushed somewhere, yet doing nothing much. Mmm, just thinking out aloud.

Sounds like an aftermarket m/c. They have a history of poor quality. Sometimes they can just push fluid around internally when not working like a real one.

 

Blown master cylinder seals.

If the system is truly blead, and the pedal is going to the floor, then the fluid is going past the seals back into the reservoirs.

 

The pedal actually stops about 2 and one half inches off the floor

 

The pedal stops about two and one half inches off the floor. Seriously scary!

 

Okay, so it goes a long way before it stops.
But, the question remains, how high is the pedal to start with?

And, with the bleeders open, can the pedal actually go all the way to the floor?

Just trying to establish how much pedal travel there is in total etc. to get a handle on how far it goes before having any meaningful effect.

And... at 2.5 inches from the floor, is it rock solid or will it slowly bleed down after that?

 

The first master cylinder I put in was from a speed shop in South Carolina. It was made in America.

 

To startwith it is 7 inches off the floor when at rest

 

Rear shoes adjusted properly? Too loose, will cause low pedal.

 

rear shoes are adjusted properly

 

with bleeders open it goes all the way to the floor, When things were working properly, the pedal would stop at about two and a half inches from the TOP.

 

Wondering if you need a step bore/quick-take-up master cylinder. If you have low drag calipers, you may need one.

 

I have read that the master cylinders with holes on both sides, need both sides to be bled.

 

No mention. New shoes by any chance?

 

Rear brakes have approximately 8000 miles, and have been adjusted.

 

Ill have to check into that tomorrow.

 

Brake hose swelling ????

 

Adjust the push rod to the master cylinder.

 

Just thinking out loud here but could you block off one side of the mc with a line plug eliminating the front or the rears to see if you can isolate the issue to front or back?

 

Checked that, as I have stainless hoses to the front calipers .

 

Brake Booster push rod to master cylinder clearance is set at .020 as recommended .