'39 Ford Master Cylinder Adjustment

G

GDORNFELD

Junior Member
It has been a long time since I installed the brake master cylinder. The rod was misadjusted and I had the problem of brake lockup, due to the bypass port being covered.

It is time to replace the brake master cylinder and I do not want to have the same problem. What is the procedure to adjust the rod length to insure the bypass port is not covered?
 
GDORNFELD said:
It has been a long time since I installed the brake master cylinder. The rod was misadjusted and I had the problem of brake lockup, due to the bypass port being covered.

It is time to replace the brake master cylinder and I do not want to have the same problem. What is the procedure to adjust the rod length to insure the bypass port is not covered?
Click to expand...

You may well find that the rod length will be okay as it currently is. I'd suggest you install the new master cylinder and see how the brakes perform.
Me? I like a brake peddle that doesn't have to travel more than an inch or so prior to obtaining some braking. That requires a few "trips" beneath the car. I adjust it (the rod) as long as possible without the master locking up.

By the way, NAPA sells NEW master cylinders for around $52 outright. I have installed many and all were perfect. In fact, a few even had the concourse correct casting and fill cap.
 
If you get under the car and feel the rod while pulling the pedal arm to apply the brakes,you can feel when the rod touches the piston in the cylinder. There should be just a touch of free play in the rod before it moves the piston in the cylinder. At rest the rod should have enough free play to be able to jiggle it with no tension.



Terry
 
You can observe the recuperation port through the filler hole. You will see a squirt of fluid ath this port as the brakes are applied. (This can cause a mess) before now I have shimmed the piston so that the squirt is minimised, but still happening. This cuts down on wasted travel before the pressure starts to build up. Once this is set, the pushrod can be adjusted to ensure the correct amount of free play, which should minimal. If the free play is not there the pushrod may prevent the port from opening and this causes brakes to lock up as pressure in the system gets locked in, and gets worse as fluid temperatures rise.

Mart.
 
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An important point that hasn't been addressed is to make sure the pedal has it's own return spring that can fully return the pedal. This will allow minimum push rod-to-master cylinder clearance (I like about .030") without worry of dragging brakes.
 
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