I have 4 wheel disc brakes on my 72 GS. Rears are the early Cadillac conversion that use the same d52 calipers as the ones on the front of our cars in stock form. I also recently replaced my master cylinder (1976 vette version). Anyway, all was ok after the master replacement awhile back. I decided I wanted to upgrade the pads. Replaced all 4 wheels. I did have to push the caliper pistons back in to fit the new pads. Went to start seating in new pads, peddle falls to floor. Bled all 4 wheels twice, peddle still falls to floor. The master never went low on fluid. Any ideas? Bleed master? Could I have screwed up my master somehow? Someone also told me I could have an issue in my proportioning valve. Possible? I have replaced disc pads many times in my life......never ran into this issue. Input appreciated.
Which valve are you using right now? I would imagine with 4 wheel disc you can just use a distribution block or an adjustable unit.
I am using the stock proportioning valve. I know some say you can't with 4 wheel discs.....but I have had them on working great for years. All I did was replace the pads and now peddle falls. Been doing some reading on the net. Some say that pushing the caliper piston back in without cracking the bleed screw can mess up the master. I pushed all 4 back without cracking any bleed screws. Think I messed up my master cylinder?
I've replaced pads that way for years. Unless it did something to the combo value, I can't imagine it hurt the master. The only thing I can think of is there is a residual valve in the combo if you haven't swapped from a disc/drum to a disc/disc combo valve. If it was drum/drum, you might only have a distribution valve. Sounds like combo valve has been tripped but I don't know how to fix it. I put a Right Stuff rear disc kit on mine with parking brake. I used the distribution block that I've always had, removed the hold-off valve and barely need an adjustable prop valve that I'm plumbing in now. I'm curious to hear what it finally turns out to be.
The combination valve being 'tripped" wouldnt cause this IMO. Inside the combo valve is a differential switch. if both sides of the switch have equal pressure, the brake light will remain off. If the pressure gets low on one side of the switch, the light will come on. Sometimes it takes a few hard jabs at the brake pedal to reset the valve back in the center to turn the lite off. I cant see how pushing the pistons back would cause no brake pedal. Do they pump up at all? The master may have developed an internal leak somehow.
I do have some brakes. They don't really pump up. Any semi hard braking will cause peddle to go about half way down and red brake light will come on. I ordered in another master (cheap at $25) to see if that will fix it.
Pressure bleeding is the right way to go. Also, if you pushed the pedal all the way to the floor several times in the process of attempting to bleed your brakes, you may have aced the master cylinder.
I dont know what year rear calipers that you have but I know that some of them with the rear e brake built in you must spin them as you collapse them. Make sure that your pads are close or adjusted on the rear. <o></o> <o></o> Nelson<o></o>
you have already figgured it out,,, the increased pressure from the new parts you installed caused the old seals to fain in the old master cyl. ,,,, when you replace it that should fix it.... :laugh:
Ok, bad master cylinder was it. The master wasn't old.....but a remanufactured 77 corvette unit with less than 100 miles on it....but it still failed somehow with my pad change. I put a new one on, bled it, and have brakes again. Still surprised at the mechanism of failure.
