second night of having the car back on the road, and i lost my brakes tonight. they worked great yesterday on my first day out. left the driveway tonight, and they werent working, wtf?? ok, the cold hard facts: *1960 pontiac catalina *converted to a dual res master and power booster from a 78 corvette.( did it a year ago, worked awesome) *it has residual valves in line *drums all around *no fluid loss in the resevoirs *been sitting for 3 months while i dicked with a motor swap. *yes, the vacuum line is hooked up when i apply the brakes, the pedal moves as it should for a few inches, then gets hard, and wont stop the car. i'm getting SOME braking, but not enough to completely stop. any ideas? master cylinder?? booster?? oh, did i mention that brakes run a very close second to electrical when it comes to things i hate to work on??
Are you using a disc/drum valve on drum/drum? Does the rod in the master have free play? I bet you only have rear brakes
ive got the 10lb wilwood residual valves. the master is actually set up for front disk, rear drums, however it has worked flawlessly for over a year.
I'd check for a failed seal with in the master cylinder. You may be moving fluid internally without being able to direct any pressure into the lines. 3 months is plenty of time for a little rubber piece to dry up and fial at first use.
Some-times the booster goes bad,when it does the thing will fill with brake fluid and the brakes go away. Check there is no fluid in the booster if clear check the vaccum line has not collapsed,this can happen over time if not being used. john
Sounds to me like you're losin' power to the power brakes. The booster is not doin' it's job. You said it feels good, then gets real hard, but not much stopping power? Listen to see if you can hear a vacuum leak on the boodter while runnin'. I'm not sure, but that's where I'd start. The way the power aspect works is when you apply your brakes the booster kicks in and helps you push, basically. Usually when you lose the power, the pedal feels harder because you're not gettin' the assist. I think that is where I would start.
ok, well there shouldn't be any fluid in the booster, cause i've lost NONE in the master cylinder. the seal going bad on the piston sounds like a good posibility. oh, the vaccuum line is good, i checked.
You've already checked to see if you have fluid leaking through the firewall at where the rod passes through.
I had a GM master cylinder go out on me once, I lost my front brakes. I believe it was caused by an internal leak, like what was described above. Once I replaced the MC, everything was fine.
yeah, as i've sat here and thought about it, and read the replies, i'm fairly confident that the m/c is to blame. i'll pick up a rebuild kit or a new m/c tomorrow and throw it in so i can get the green car on the road for st. pats day.
Have you tried re-bleeding the brakes ? I had a wierd problem last year where the brakes bled up fine and worked ok for a few miles, but then the pedal went to the floor like you described. Bleeding the rear brakes fixed it for another few miles. My best guess was that it was a defective residual valve. It didn't hold any pressure in the rear brakes, which allowed air into the rear brake lines past the wheel cylinder cups. Replaced the master cylinder and it has been perfect ever since.
Make sure you have vacuum to the booster. Pull the hose and verify that it has vacuum. Sometimes the little plastic valve goes bad and causes problems. I almost parked my GS under a Garbage truck do to a vacuum problem. It was working fine under "Normal conditions"..but when I needed it.....
I agree change your master cylinder, you have either only fronts or only rear brakes and that is why the pedal feels ok 1/2 way through your stroke then get rock hard.
if the pedal gets hard during normal travel you have a vacum assist(the power part of power brakes) problem. collapsed hose to booster, bad booster, sometimes the port in the intake gets clogged & won't pass vacum. if you can push really hard on the pedal & the car stops better that confirms it. hope that helps...mel
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