Master Cylinder

Hi Bill,
You describe an internal leak in the brake system. When the peddle is at rest
there is normally an open flow of fluid between the master cylinder and the
revisor. There is a check valve somewhere in this flow path. When you step
on the brake the check valve stops the flow of the brake fluid from returning
to the revisor, allowing the fluid to go to the brake slave cylinders. Your
internal leak is in the check valve. The most minute piece of dirt in this
devise will render it defective. Your problem is that the fluid is going back
to the revisor instead of out to the brake slaves. WITH CAUTION !!! -----
Remove the Master Cylinder filler cap and have someone SLOWLY step on the
brake. When the check valve is defective you should see the fluid coming back
into the revisor, usually in the form of bubbles. A small amount of flow is
normal as the check valve does no seal instantaneously. Be careful as I have
seen this so severe that it blows fluid right out the top of the filler. The
check valve is usually part of the rebuild kit. We have put as many as five
remanufactured master cylinders on some cars before finding one that works.
When you pump the peddle rapidly and the brakes hold, you are pumping fast
enough to bypass the valve. The check valve can be separate from the piston
or built into the piston. We have seen them installed backward, but they
usually can only go in one way. When overhauling brake components — keep it
surgically clean. Good luck AL Diamant