Brake pedal travel with shoes locked up

[Sigurd]

I am curious to know how much brake pedal travel there would be if the shoes were adjusted tight to the drum. I bled the brakes yesterday with a helper and still had quite a bit of air, so I made a homemade power bleeder with an old cap and my air compressor. That got all the air out and the pedal stops hard about halfway down. Does this sound right? I haven't driven the car in over 10 years and I just don't remember.

[Pruneman99]

[Sigurd]

Yeah, that's exactly what's happening. On each corner, I tightened one shoe until I could barely turn the drum, then tightened the other shoe. There's about half a stroke of pedal travel.

[Pruneman99]

The pin that works the master may have the incorrect amount of free play. There is a specified gap, but I can't remember it off hand.

Basically you don't want the pin engaged when the pedal is released, and not a huge gap where you use half of the travel just taking up the gap.

[viiking]

[Pruneman99]

Yes, stop plate first. Forgot about that.

[Sigurd]

Yes, I have the stop plate adjusted so that there is about 8" of pedal stroke, measured from the pedal to the bulkhead. Then, I adjusted the rod so there is about 3/16" play at the pedal.

My first attempt was to bleed the brakes normally with a helper. The pedal moves fluid out of each wheel cylinder. This is a dual circuit MC. If there was a problem with one of the pistons in the MC, would I still get fluid at all four corners?

My second attempt with the shoes locked up and power bleeding, the pedal feels great, but it seems to be hitting so low considering there's nowhere for the fluid to go.

[Sigurd]

I was sure I had enough pushrod play, about 3/16", but I shortened it some more to provide around 9/32" or 1/4". I also backed the shoes off to have a slight drag and power-bled again. The pedal doesn't stop until 3/4 of the way down.

I have never struggled with this before. When I had it running, this car could lock up all four corners with great pedal feel. It's the same MC that I installed 10 years ago. Now, the system was open and empty during the time the car sat. I'm suspecting that there is some rust or something inside the MC that is causing one or both of the pistons to not fully travel. I'm going to remove it and have a look.

[Sigurd]

I removed and disassembled the master cylinder and I'm glad I did. Rust and sludge and the front piston's compensating port completely blocked. The pistons looked good and the rubber seals were pliable. I'm going to take the parts to the solvent tank at work, clean them, and try again.

[AirHead1966]

Are you sure your rubber lines are in good condition? If they are expanding/bulging when you press the brakes, you will see pedal play with the shoes locked.

[Sigurd]

Yes, they are new as of a few years ago.