The Stovebolt Site Forums The Shop Area Driveline Master Cylinder Issue: Port stopped working.

Problem is just as the title says. Namely the front port.

Relevant info is: It's a 1957 Chevy Pickup. I switched from a single master to a dual reservoir master. Unfortunately I ordered the wrong one, so I had to plug 2 of the ports but I checked and that's not causing the problem.

I bench bled it, and both ports I am using bled into their respective reservoirs just fine. I mounted it, bled the back brakes just fine with the lid off, but when I went to bleed the fronts, I got pedal resistance and no fluid. I assumed I had screwed something up in the lines since it's my first time doing brakes... until I finally pulled the line right out of the master. Absolutely no fluid directly from the front port. I used the plastic tip to make sure the port was clear, and still nothing.

The port worked just fine 10 minutes before when I bench bled it, the reservoir is full, and yet no fluid all of a sudden.

All I can think of is maybe some dust fell in through the inspection hole as I was working and plugged that port because other than that I have absolutely no clue.

Any ideas?

just a thought, since you changed from the original master cylinder to a dual resivior,did you change the adjustment on the pushrod? Maybe to long or to short and not allowing the piston to clear the port when the piston moves.

Hy VanattiWorkshop, "Tommy" has a very good point, check the pushrod adjustment to make sure there is a clearance when the master cylinder pistons have returned to their at rest positions. Are your brakes still drum all around? Did you plumb the rear brakes into the primary circuit of the master cylinder (closest port to pedal)?

Yeah, that was a really good point. I checked it this morning, an unfortunately it didn't help.

Out of slight frustration, I pulled the master again to try and bench bleed it. I also tried cleaning the front reservoirs port with a guitar E string (very small wire). Sure enough, on the bench it wouldn't bleed from that port. I pushed a bit harder, there was a loud pop and the master came unstuck from the vise and brake fluid splashed a bit. Suddenly after that, the front port started bleeding again.

I remounted it, rebled the backs but I still have an issue. The front brakes bled, but the pedal was EXTREMELY tight and each front wheel took about 20 pushes to fill my catch can. With the back wheels, the pedal goes to the floor easily and the can fills in about 6 pushes when bleeding.

Is this normal or is it sounding like the master might be bad?

Found a small leak, repaired it. Same problem. Maybe it's meant to be that way, putting more pressure on the rear brakes? Not sure on this one at all.

Hy VanattiWorkshop, the way the dual master cylinder works if the primary system is bled and tight, then you only get a small amount of movement on the secondary system piston. Try opening a rear bleed screw while bleeding the front brakes, that should allow a full stroke of the secondary piston. Don't forget to adjust all your brakes up correctly before checking on your pedal, hope that helps.

Perfect, thank you!