Chaotic cuda

Okay guys, I have a brake issue. I have a 70 Cuda with power brakes, I recently switched my rear drums to disk. Bled the brakes a bunch of times and got them good and stiff. When I start the car and press the pedal, it goes to the floor. Re-bled (no signs of air in lines) and the same thing. Shut the car off an pump the pedal 2-3 times and it's stiff again. I'm leaning towards the boosters bad. Any ideas?
Thanks.

Archer

CC -

Do you have a break cylinder proportioning valve and if so did you reset it for the new discs?

Archer

Chaotic cuda

I do have a prop valve installed. I didn't reset it though. Not sure how to do that.

Drag Pak

Did you put a disc brake master cylinder in? I believe the drum brake MC will have a residual valve in it on the front/forwardmost port.

Chaotic cuda

Yeah I installed a disc brake master cylinder. I installed disc brakes on the front last year with all new booster, master cylinder, prop valve, and lines. It worked good but not great. So this winter I changed the rear to disc and installed a line lock on the front.
Bought the rear disc set up from Right Stuff. they say its a bolt on kit and shouldn't need to change any of the other components.

Drag Pak

I seem to recall the same issue. Fought it for several tries to resolve. I had to put a 2 lb residual valve in my manual rear disc brakes to get them happy. Although on a drag car we run the MC outlets reversed due to the skinny front tires, and no proportioning valve.


Are you bleeding from rr, to lr, to rf, to lf?

Rooty

If your booster is OK and you have enough vacuum here's the way to tell. Get in the car and push the brake pedal a few times to expell any residual vacuum that may be present in the booster. Holding the pedal down lightly with your foot, start the car. The pedal should push back towards you but not fully. If this does not happen a booster rebuild is probably required. Do not toss good money away for nothing so go here for the complete story

http://forums.hotrod.com/car-craft/7...brake-booster/

DDodger

the calipers have the bleeders at "very top" ? some calipers can be reversed left to right side, putting bleeder "down"

"what" are these calipers? what sort of setup for emergency (parking) do they have?

moparted

u need a master cylinder designed for 4 wheel disk

Chaotic cuda

Thanks for this information. I did this and the pedal swent down not up.

Chaotic cuda

The master cylinder has nothing to do with what kind of brakes you have. It pushes out the same pressure from both ports. The prop value is what regulates the pressure.

Chaotic cuda

Bleeders are up on both sides. No E-brake. Even tried taking them off and bench bleeding. What a pain in the rear that was.

Drag Pak

I think you better "Google" it! As you are not listening!

Rooty

If the pedal goes down, then perhaps the clearance between the master and booster rod is too shallow or the weight of the pedal is causing booster actuation inadvertently. I've seen this happen before and some people put a spring on the pedal arm to ensure it returns to the upper bumper completely. Pedal ratio is quite different for various braking schemes - manual, power, hydra boost and different bores of master cylinders which have varying strokes. This may not be your case but ensure above all else that the master retracts completely. You can measure the stroke depth of the piston when bleeding the master but it's hard to tell weather said piston is pushing back on the booster pin or not. Care full measuring is required to find this gap and the pedal must be held back completely. Perhaps your just not moving enough volume of brake fluid to actuate both front and rear pistons or your line plumbing is not correct. Good luck and don't get frustrated because there's always an answer - you just need to find it.