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Old Jun 8, 2012 | 04:24 PM
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fdevole
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Default Brakes

I rebuilt the mastercylinder on my 78 and have bled the brakes 3 times, each time I get good pedal, then I drive it about 10 miles and the pedal goes to the floor and the brake light comes on, I can find no leaks and get a very small amount of air when bled. Where do I go from here?
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Old Jun 8, 2012 | 04:54 PM
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Originally Posted by fdevole
I rebuilt the mastercylinder on my 78 and have bled the brakes 3 times, each time I get good pedal, then I drive it about 10 miles and the pedal goes to the floor and the brake light comes on, I can find no leaks and get a very small amount of air when bled. Where do I go from here?
If you get air, no matter how small an amount, every time you bleed one of two things is happening. Either your not getting all the air out, or you have a leak your not finding. I'd start with the bleeding method. The old pump hand hold approach is okay, the vacuum method a bit better, the gravity way is pretty good, but the power bleeder seems to be the easiest surest way to get the air out. Don't forget, there are two bleeders on the rear calipers too. If that doesn't do it, you've got a leak somewhere, which is what I'd suspect.
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Old Jun 8, 2012 | 05:14 PM
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I always work solo and brake bleeding was always a PITA and a challenge. A while back I decided to solve that problem and made the one pictured from garage scraps. With my pressure regulator set 18-20 psi, I just crack open the bleeders in the correct sequence and job quickly done. Either you are not getting all the air out of the system, or you have a leak. Check your master for any loss of fluid. If your pedal goes to the floor, you have a leak somewhere.
[IMG][/IMG]

Last edited by Red 69; Jun 8, 2012 at 05:19 PM.
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Old Jun 8, 2012 | 05:19 PM
  #4  
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Mike Ward
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Originally Posted by fdevole
I rebuilt the mastercylinder on my 78 and have bled the brakes 3 times, each time I get good pedal, then I drive it about 10 miles and the pedal goes to the floor and the brake light comes on, I can find no leaks and get a very small amount of air when bled. Where do I go from here?
Stop futzing around with the master cylinder- that's got nothing to do with it. The wheel where you're finding air most probably has an unacceptably high amount of lateral runout on the rotor surface. This causes pad 'knock back' and draws air into the caliper. Normally happens at about the 10 mile mark in a severe case.

Have you changed or played with the rotors lately?
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Old Jun 9, 2012 | 10:35 PM
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I agree, which wheel are you getting air in? is it the same wheel every time? replace that caliper and replace that rotor, or rebuild that wheel's caliper with O-ring seals.
if it is on the rear ( usually is ) then you might have a rear bearing worn out or out of spec causing excessive runout. if you are lucky it is just runout from a overheated warped rotor. replace it...

if you pull your lip seal out from the caliper in question, i bet you will find your leak.
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