Master cylinders are made so that fluid is trapped between the piston and
outlet. Then when the pedal returns (foot off) the piston is supposed to
come back to rest against the washer / snap ring in the pedal end of the
master cylinder. This uncovers an opening so that fluid will both pass back
into the reservoir, and the cylinder can again fill. Something may be wrong
with that part of the operation.
Perhaps it is that little doober down in the bottom of the cylinder that
acts like a little valve. Perhaps a spring inside the cylinder is broken,
rubbing, etc. Or, maybe, the pedal / pushrod arrangement is adjusted so the
piston cannot fully return.
I once had a vehicle that had this problem and it drove me nuts. On that
particular vehicle, all this was handled by two holes drilled between the
reservoir and the cylinder. It took me months to figure out that one of the
holes was not drilled clear through -- I suppose the guy on the drill press
broke a drill off and didn't bother to check the last piece he made.
At 03:00 PM 8/24/03 -0700, Joe Curry wrote:
>OK, guys, I need some help here. I installed the Tilton brake
>proportioning assembly on dual master cylinders to be able to adjust the
>proportion front to back, as several suggested.
>
>Today I tried it out. The result is that the brakes lock up and will
>not let go until I release one of the bleed valve on the calipers.
>
>I used clutch masters because I had them on hand and they are the same
>size as a brake master for an early Spit except for the reservoir.
>Question is, despite the same bore size, is there something else that
>might be different and keep the pressure on the line after the pedal is
>released?
>
>I can probably come up with a pair of brake masters if they are indeed
>different, but as far as I can see, they are not.
>
>What else could be causing this? I tried different size actuator arms
>and hage induced free travel in the linkage but I can't seem to find the
>cause of this problem.
>
>One more thing, there is no free pedal play with this system. The rear
>brake master has very little play before they grab and the fronts do go
>in a little further but appear to keep the piston in place after the
>pedal pressure is released.
>
>I disassembled the master cylinders and inspected the springs and they
>are strong. So what gives here? Anyone???
>
>Regards,
>Joe (C)
>
>P.S. I did alright today at the autocross. 4th overall despite having
>to drive through locked brakes! :)
uncle jack
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