a year ago I installed a new master cylinder, new ford proportioning valve, and went through brakes on 1979 f250 4x4. New booster, new drums, new shoes, new pads, blahh blahh blaaahhh!! Now, every time I need a lucky brake, I hit the fat pedal and irrch! best brakes the truck has ever had. Every time I popthe top of the MC, the big compartment overflows fluid, leaks it back out, even if Ileave the level 3/8" from the top and fill the smaller compartment full, the smaller compartment goes down to half or so, is this a defective mastercylinder or a defective proportioning valve?

 

50/50 chance....

I'd replace whichever is cheaper .... likely the MC in my opinion.

 

yeah; I'm afraid that that is the concern. I love the bleeding, no rest for a few days, pump pump pump shoot pump pump fill pump pump pee pump pump pump fill squirt, "ooohhh, more floor dry" !!!!

 

I made a auto bleeder out of a jar and some tubing. I hook it to vacuum on a different car. Not pretty but one of the best ideas I ever had.

 

......>>>>>> OK!! I replaced the lid tonight. Going to seeif the fluid was coming through rubber seal between the reservoirs. RESERVOIR!! I want to gofishing, forget he brakes!!

 

A quick way to test the proportioning valve for leakage is to unscrew the switch. If fluid leaks out then the valve is bad.
My money is on the m/c.

 

ok thanks. I want to give a chance with the new lid, it is much betterfitting than the old one.

 

I put a new lid on her, seems better. Will follow up later.