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I'm one of those "Horrible" people, who has owned and worked on 6 Corvettes. And have NEVER had an issue bleeding brakes. Vacuum bleeders DO NOT work on C2 and C3 Corvettes. Lip seals seal the other way! Sucking against the lip seal WILL pull in air. Pump like mad with your mity vac. Your only making it worse. Properly bench bleed the master. Pressure bleed or gravity bleed the brakes. Never, not once a problem.
I have one more question before I lock this car up with Al Capone. I made a pressure bleeder. After finally getting it to seal at the M/C I bled all 4 wheels. I saw no bubbles. Had more flow from the rears but no air. Pedal great after bleeding but upon start up, back to floor. What do you do if you discover there is run out????? Will run out occur on all rotors or on various ones??
I have one more question before I lock this car up with Al Capone. I made a pressure bleeder. After finally getting it to seal at the M/C I bled all 4 wheels. I saw no bubbles. Had more flow from the rears but no air. Pedal great after bleeding but upon start up, back to floor. What do you do if you discover there is run out????? Will run out occur on all rotors or on various ones??
Runout will only affect your brakes once the vehicle in motion - two much runout at the wheel causes the rotors to force the caliper pistons in and out quickly, which causes air to enter the system. It can occur at each rotor independently. In my case, it was just the right rear wheel, and the runout was caused by the spindle.
If you bled all four wheels, got a firm pedal, started the car and then the pedal went to the floor without driving the car (and I'm talking about driving the car for miles at speeds of at least 45 mph) then runout is not your problem.
If you have a rock hard pedal without the engine running and yet the pedal goes to the floor when it is running then the issue is with the booster. FWIW on my '70 the pedal travel with the engine running is a lot more than it is for example my C4. If you took the car onto a deserted flat road and stood on the brakes at 30 mph will all the wheels lock up?
Haven't tried to lock up brakes, but i'll give it a shot. I blocked M/C and removed. the shallow hole in the M/C would make it correct and the short rod with it barely sticking out indicates the booster is correct. Both new but it's anyone's guess if the are worth a crap.
I appreciate the help. been fighting battle sense March. Could it be that when the 2 back brakes failed initially that there is a problem with the combination valve?????
If you can pump fluid out of the back brakes I doubt that the combination valve is causing an issue. However I just happened to skip to related issues that are part of your thread and back in 2015 another forum member was having a similar issue as you -
been playing with this for years . when I first start the car I have a normal brake pedal . but the car will roll to a stop the brakes have very little to do with the stop .after the car is warm the brakes are fine . I have had them bled multiple times . changed the master cylinder . have replace all 4 calipers in the last couple years . I do not have a hard pedal and if I try to stop when cold the pedal does not go all the way to the floor it seems normal . any ideas even took it to a place that has rebuilt vets for years .
Outcome -
have brakes now . it was the booster . the one I had ordered from napa was suppose to be the exact replacement . was going to do it myself but decided to have my mechanic do it took him 1 1/2 hour and he has all the right tools . only problem now is it seems the pedal is to high but he says its adjusted as far as it will go . I will have to get use to it . been playing with this for years .
Have you seen this?
Got a soft brake pedal? Don't forget to check the brake booster pin clearance. Brake booster pin clearance
I may have figured it out. The NEW Booster is defective. I plugged the vacuum line to the booster and I have a pedal running and not running. When I replace the line into the booster, pedal goes back to floor when running.
Does this sound like the issue is resolved? Boy, I SURE HOPE SO.
I may have figured it out. The NEW Booster is defective. I plugged the vacuum line to the booster and I have a pedal running and not running. When I replace the line into the booster, pedal goes back to floor when running.
Does this sound like the issue is resolved? Boy, I SURE HOPE SO. Rod in booster is spot on.
If you can not stand on the brake pedal all day long and I mean with the T-Top off, using both feet, stand on the pedal. If you can not, then look no further than the MC.
It does not matter if engine is running or off, you should be able to stand on the pedal with absolutely no give.
I hope you didn't use a bolt or a pipe plug to block the MC ports. I don't believe those are NPT. Deep inside those ports are flare fittings. If you thread something in there other than a flare fitting you will damage the flare. Anytime you want to block the ports for test purposes, purchase a ready made short brakeline that already has the correct fitting on the end. Then simply bend the other end to pinch off the line. And each port takes a different diameter and thread pitch. So for about $15, you have two test-lines forever.
In your first post you mentioned new MC. I will assume it was bench bled. But more importantly, how far did you shove the piston in its bore while mounted in the vise? If you went more than 1 3/8 inches, your brand new MC is toast. You damaged the piston seals and voided the warranty.
See my profile > photo album > brake bleeding.
Last edited by HeadsU.P.; Sep 24, 2020 at 03:11 PM.
