We've almost finished repairing and reassembling the front disc brakes on
our '66 MGB but have run into some problems.
The story goes: one of our front disc pads wore all the down to the metal and
badly scarred the rotor... So we decided to turn the rotors and replace all
four disc pads. On the side which had worn all the way down, the other disc
pad was fine, making us think that maybe we had a sticky caliper... So we
decided to rebuild both calipers, replacing the seals and the sealing rings.
In the process of doing this, we removed the calipers from the car, took all
the pistons out (using a bicycle pump to force them out), cleaned them up,
relubricated them, put the new seals in, put the cleaned pistons in,
and voila, they were ready to go back on the car.
After putting them on, we tried bleeding the lines but we can never get good
pressure in the brakes. If we pump once, the rotors are able to turn freely.
If we pump several times, pressure builds in the pedal and the brakes seize
the rotors. After releasing the pedal and waiting 5-10 seconds, the rotors
turn freely again. It seems like there's probably a lot of air in the calipers
somewhere, although no more bubbles come out when we try to repeat the bleeding.
Did we do something wrong??? Is there a way to displace the air that gets in
the cylinders when the pistons are removed and then inserted during the
rebuilding? (or should normal bleeding do this?). Maybe after cleaning some
gunk out of the pistons, they now leak? Only one was slightly scratched.
Is it likely that the rear brakes will also have to be bled?
Thanks mucho,
Lydia gregoret@cgl.ucsf.edu and Chuck wilson@msg.ucsf.edu
P.S. while the calipers were off the car, the brake lines were covered
with saran wrap and twist-tied. The cap on the master cylinder reservoir
had saran wrap under it and was tightly screwed on. The car was sitting like
this for four days under a car cover.
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