58´ Century Power Brake Fail

Discussion in 'Classic Buicks' started by Century58, Aug 16, 2020.

  1. Century58

    Century58 Guest

    Hello, I own a '58 Buick Century with power brakes (Delco). I had problems with missing power brakes all the time. I used silicone brake fluid.
    In the garage the whole brake system was overhauled and changed to normal brake fluid. New hoses, new brake cylinders. The master brake cylinder and the brake booster were overhauled with new gasket sets. Now it brakes much better, but it loses the brake power support from time to time. The booster tank was checked with pressure and smoke for leakage. Nothing to find.
    After 2 times braking or when I drive with lightly applied brakes the support is gone and I have to brake "normally".
    The windshield wiper hangs on the vacuum line. There seems to be something wrong, because when the engine is running it "bubbles" in the water glass. Can this be the Problem? But According to the manual there must be a check valve somewhere. Where exactly? Is it the T-piece on Picture 2888?Does anybody else have an idea for troubleshooting? Modifications are not an option because of originality.

    Regards Andre
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  2. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    This is the check valve.
     

    Attached Files:

  3. Century58

    Century58 Guest

  4. Century58

    Century58 Guest

    I've run some tests now.
    First, I checked the check-valve. Seems to be working, because there's no passage to the brake booster. Then I checked the tank with a brake bleeder vacuum pump.
    Although only with -7,3PSI (0,5bar) - thought the value on the scale was -15 "bar", but it was "inHG" - so much less vacuum - but the vacuum remained stable.
    Then I disconnected the line to the wiper and sealed it. Immediately I had it in my hand, because the pipe at the wiper motor had come loose from the pressing.
    With the second check I had to find out that the hoses could be pulled off the pipes very easily. Partly even if they had a clamp. Thought already that is the error and replaced all hoses. Unfortunately the brake performance did not improve.
    I have to do the "Testing Power Brake Unit" from the manual again. Had the feeling that during test "1st Vacuum Assist", I did not feel any brake support. Probably hadn't pumped with the pedal often enough to empty the system.
    Test 3 "Vacuum Leak" I can probably save myself, because I can only brake assisted 2 times, sometimes not at all.
    How much vacuum does the motor have to provide? I think I will do some new tests and put the pressure gauge after the valve. On the one hand to see if vacuum is built up, how much and if the valve is really tight.
    I also had the manometer in the pipe to the tank - instead of the tank. Strangely enough, the vacuum was not stable there and dropped again and again - that's why I changed the surface. I have to take a more structured approach and work through the lines point by point.
    Can it actually work without the tank?
    In the attachment you can see a picture of how the lines run in my case.
    I'll keep you informed.
    Unbenannt.png
     
  5. Century58

    Century58 Guest

    Found it myself in the Manual. The Engine must have 22inHG on 1600RPM
    22inHG = 10PSI = 0,7bar
     
  6. Century58

    Century58 Guest

    I'm a little confused. I read a bit on the internet and found out that Buick from 57-58 used an oil pump with a flanged vacuum pump. I assume that this pump is responsible for the vacuum for the wiper and the brake. Now an "expert" told me that this vacuum pump is only for the wiper and has nothing to do with the brake. Why then are both things connected there and pictures in the internet of 58er engine compartments show the same picture? The manual is somehow not very helpful
     
  7. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    The vacuum line from the vacuum pump/oil pump goes straight to the wiper motor.
     
    Max Damage likes this.

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