Hard brake pedal

[Spinner01]

I posted in another thread but didn't get a response. Hopefully, somebody out there has some input. Thanks in advance for any help.

I recently had a spongey pedal that required pumping to build pressure. I found no leaks at the wheels, lines or the MC. I bled the lines at all wheels and a very small amount of air was found at the drivers rear. The spongey pedal persisted - basically no change. I then adjusted the vacuum booster rod (counter clockwise) and got a hard pedal. While adjusting, I heard vacuum escaping from the booster through the rod opening. At this time the pedal was actually too hard with almost no travel, so I adjusted it again clockwise about 1 full turn. All was good at the pedal for a day or so, then the pedal became too hard again. I adjusted it clockwise again about a half turn -- heard air escaping again -- reassembled and then had a spongey pedal. Adjusted counter clockwise again a half turn or so and the pedal is good again. But likely not for long. I'm thinking of replacing the booster. Does this sound reasonable? (1968 F250 Camper Special - all drums).

[colnago]

I think it sounds like you need a new booster, and that you need to bench bleed the MC. You should have some play between the pedal, and it starts to engage the hydraulics, so that when you release the pedal, the hydraulics release completely, but you don't want so much that you have a bunch of pedal travel (0.050 between the booster plunger and the MC, IIRC). Sounds like you're in the ball park, though, if 1/4 turn makes a big difference. With the spongy brakes, it's gotta be air. The most likely place is the MC, which means time to do a bench bleed.

Just out of curiosity, where is the booster getting its vacuum? Have you put a vacuum gauge up to measure at all?

Joseph

[Spinner01]

It pulls vacuum from the passenger side of the intake manifold. I haven't put a vacuum meter on it (I don't have one but could get one). I have pulled the vacuum line out of the booster while it's running and there seems to be quite a bit, but I don't actually know what the proper amount would be.