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master brake cylinder still bad?

P pantdinoMember
So after rebuilding all my calipers and switching back to DOT 4 fluid, even without the engine running I found
the brake pedal would just go all the way to the floor with only mild
resistance, while making a swooshing or mechanical wheezing sound.
I took the master cyl to the local Napa store but we were unable to identify
which new one would replace it( it is an aftermarket cylinder, but I have no idea which one), so I sent it out for rebuilding.

Brought it home, bled all the lines, and the brakes are doing exactly the same
thing-- pedal behaves in same way (engine not running).. No change in fluid
levels in the reservoir, no leaks. There was no fluid at the pushrod end of the
m/c when I took it off before.

AFAIK there are 1.0 possibilities-- the master cyl main seals are letting the
fluid pass from one chamber to the other inside.
Which means the "rebuild" job wasn't done at all or was done poorly.

Any other ideas?

Jim
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sickcatsickcatMember
Welp,
Welcome, sounds too familiar. I had this same problem on the clutch side, I was using a MITY VAC to pull fluid threw but before I could get the bleed screw tight it seemed to allow air to draw in, if you bleed with the pedal it may be that the little shuttle valve is cutting off your flow to the brakes as designed sensing a brake or what it thinks to be a brake in the line. ie front and rear system? I have not figured threw this but maybe a pressure bled set up would have a better out come. By the way the vacuum way was miserable at best, I finally went with; http://www.speedbleeder.com/ these helped but were not a cure all,

Mark
J jb1490Member
quote:
the brake pedal would just go all the way to the floor with only mild
resistance, while making a swooshing or mechanical wheezing sound.

These sounds are probably from the brake booster and do not indicate a problem with the booster.

Have you checked the length of the master cyl pushrod? It may be adjusted too short.

I have found that on the Hall modified front calipers, sometimes air can get trapped under the upper hex head bolt (top bolt, as installed) that is used to plug the original brake line entry point. Loosening the bolt will bleed the air, but the copper washer may not seal. The washer on mine was quite thin and would not seal completely even after I annealed it, so I had to find a new one at the auto parts store. The new one was thicker which is OK. Your idea of moving the caliper to a different position has worked for me.

John
P pantdinoMember
quote:
Originally posted by jb1490:
quote:
the brake pedal would just go all the way to the floor with only mild
resistance, while making a swooshing or mechanical wheezing sound.


I have found that on the Hall modified front calipers, sometimes air can get trapped under the upper hex head bolt (top bolt, as installed) that is used to plug the original brake line entry point. Loosening the bolt will bleed the air, but the copper washer may not seal. The washer on mine was quite thin and would not seal completely even after I annealed it, so I had to find a new one at the auto parts store. The new one was thicker which is OK. Your idea of moving the caliper to a different position has worked for me.

John


Interesting-- as I got my calipers from Hall originally the brake line entry point WAS at the top site. I changed it to the lower site as part of my recent "improvements." Sounds like whoever was doing Hall's work that day messed up.
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