55 Power Brakes - hard pedal

[tomp]

Hello, need advise
Had my brakes overhauled, everything, but now it is almost impossible to stop the car. When I touch the pedal, it starts braking normal, but then it gets just "hard" and looses brake power. The pedal is not spongy, so I guess i have got the air out. Pumping out air from the booster, holding pedal and starting the engine makes it drop just a little. I can feel it, but it is hard to measure how far it drops.
I rebuilt the Bendix PB myself with a NOS kit, so to eliminate my non-mechanical skills I ordered a rebuilt unit from US - but it works just like the one I had. Bought a new and replaced under floor Master Cylinder. Just the same. Changed the brake shoes to another brand, no gain i brake effect. Changed the brake hoses again, just in case. If I adjust the shoes very tight to the drums, it feels a little better. If i go by the book and adjust the brake anchor and back off the star adjusting screw to obtain the correct .010" upper-.015" lower between shoes and drum it looses effect.
My vacuum reads 18 inches (Eldo, 2x4). I have now mounted a vacuum tank to help out the vacuum, and it feels a little better, but not actually stops the car like it did before I overhauled the brakes.
Where do I put my attention, M/C, Bendix PB unit or the shoes/drums?
Frustrated greeting from Norway,
Tom Pettersen

[D.Yaros]

Under similar circumstances with my car I found rust in the system, necessitating wheel cylinder work/replacement.  I did not your message does not mention the wheel cylinders?

[35-709]

Is there a rubber hose between the vacuum source and the power brake booster?  I had the situation where the rubber hose looked OK on the outside but was coming apart and collapsing on the inside when vacuum tried to go through it. 

[tomp]

Thanks for looking into my brake trouble,
I did change all the wheel cylinders. Brake fluid flows easy when bleeding at each cylinder. I have removed the drum to see what happens when brakes are carefully applied, and they push the brake shoes even on both sides of cylinder. With the drums on, the brakes takes action and it is not possible to turn the drum, you can feel the shoes engage. The pedal is not pulsing, the drums are round, have been turned within the limit of .030".

I have measured the vacuum at the end of the hose too, same as manifold vacuum.
TomP

[Walter Youshock]

'55 is the Hydrovac.  I'd NEVER attempt to rebuild that booster myself, so I admire you.  Did you bleed the booster first then each wheel cylinder?  Is the leather piston in the booster lubricated?

[tomp]

Hi,
I followed the book as described, lower and upper bleeder screws on the Bendix unit. Then the wheel cylinders. The pedal is so hard that I don't think it is any air left in system.
I have also put more Delco shock absorber fluid in the vacuum chamber for the leather piston. I can hear the air coming out when applying the brakes, and the unit holds the vacuum ( I also have the tank you know) to make at least 2 stops after I turn off the engine.

I thought that the Bendix unit I overhauled myself may have an internal leak, that is why I bought a rebuilt one thru Ebay. Same failure on both?
TomP

[CEC #20099]

Tom: My guess is the Hydrovac, but since it is a remote slave booster, you might make up a flared steel line to bypass the hydrovac. The car should stop reasonably well on just the master cyl.
I have had several 55`s, & the wheel & shoe adjustments are not critical, at  all.

c chleboun # 20099

[tomp]

Yes, I think I will try to by-pass the booster to eliminate the brake shoes/drums. After Hershey..
thanks,
Tom P