Power brake booster

[Guest 49 new]

I have a 1949 Chrysler with vacu-ease power brakes. Following replacement of the brake shoes, this problem started. When I press on the brakes sometimes everything is fine, but soemtimes when I let up on the brake and then, two or three seconds later, press the brake again, the pedel goes clear to the floor. I quickly pump the brakes (only once or twice) and all is A-OK until I repeat what I Dscribed above. I have bled the brakes numerous times and have adjusted the brake pedal free-play. If I by-pass the power booster the brakes work perfect - except of course, I do not have power brakes.

[JACK M]

I would be taking a look at the master cylinder.

[Guest 49 new]

If the master cylinder was malfunctining, would the bakes work fine when I by-pass the power booster?

[JACK M]

What do you mean by bypass?

[Guest 49 new]

Thanx for you interest in helping me. Perhaps with this dialouge we can all learn someting.

This type of brake power booster is nothing like modern power boosters. The brake brake pedal "plunger" does not go directly into the power booster as is the case with modern power boosters. Rather, the plunger goes directly into the master cylinder, much as a car that does not have power brakes does. Then a brake line (with fluid in it) runs from the master cylinder into the power booster with another line running from the power booster to a junction box that feeds the wheel cylinders. The power booster has a series of valves and has a vaccuum feed much like modern power boosters.

By by-passing the power booster, I ran a line directly from the master cylinder into the junction box that feeds the wheel cylinders.

One thing that is most curious is that the brakes worked perfect until I removed the shoes to be rebuilt. Just like changing shoes on a modern car. When I put the new shoes on, the problem started.

[keiser31]

Sounds to me like another brake shoe adjustment and then another bleeding is in order. If it all worked fine and all you did was to change the shoes, then all you need to look at are the shoes. I'm thinking that you have only a couple of possibilities for something to go wrong. Either the shoes were not "fit" to the drums, the shoes are mixed up (primary/secondary shoes in the wrong positions) or the adjustment is off. I would have a hard time believing that the booster all of a sudden took a dive on you. I used to be a brake mechanic and the booster problem usually gradually goes bad.

[c49er]

I think possibly because you changed the shoes it caused a change in how far the push rods in both the booster and master cylinder travel-possibly causing the rubber cups to scrape into a dirty/pitted area of the cylinder bore and possibly damage the piston cup= internal leakage. Also by bleeding this Vacu-Ease unit, if it did have scale or sludge in it possibly did cause a port to become partially blocked. Is yours the internal or external type "Vacu-Ease unit? I have sevearl cars that use this unit. If one of the little vacumn valves which is rubber splits/ cracks the engine can suck all the brake fluid out in a few seconds and you lose your brakes! Ask me how I know! Had it happen in my 50 Royal wagon and a Dodge 3 tonner. Smokes out a 1/2 block of road!

[Guest martylum]

I agree with jack M the problem lies with the master cylinder. The booster is merely passing along amplified hydraulic pressure and should not cause a pedal to go to the floor.

I think it likely your master has dirt in the compensating port which travels back and forth blocking the port some of the time.

I would completely remove the master for disassembly and inspection. A complete flushing of the hydraulic lines if aslo a good idea. I thinking there are rusty particles in the master.

Martin Lum