1958 Bendix Treadle Vac problems

[Christian Aicher]

Hi there,

My 1958 Cadillac with a Bendix Treadle Vac brake system has developed a very hard pedal with almost no pedal travel. When applying the brakes it is almost as if there is no vacuum assist and you have to apply a lot of pressure (sometimes scary) to get the brakes to work. My 1958 Buick with a similar brake system has a "normal" pedal movement with a nice power assist. When I try to push the plunger up (at the booster, not the pedal), I can not get more than about 1/2 inch travel. Is this indicating a problem with the master cylinder (swollen seal hanging up at port?)?

Regarding the booster:
I checked the vacuum at the hose that goes from the engine to the booster and I have about 14 to 15 in Hg at idle (without check valve). When measured with the check valve in place it goes up to 20+ in Hg when reved up.
When I checked the vacuum container, I used a hand vacuum pump and pumped it to 10 in Hg vacuum and it stayed there stable without loosing vacuum for several minutes (until I pulled the plug).
However, when I try to apply vacuum to the inlet on the booster, I can not build up a vacuum, not matter how hard I try. When I connected the vacuum hose from the engine to the booster without the check valve, I mean to hear a hissing sound (difficult to determine with the engine running).
So I assume that there is an issue with the Treadle Vac, even though it was sent out for overhaul by the previous owner.

So here are my questions:

    Can the Treadle Vac be rebuild "at home" (with a repair kit for both the main cylinder and the booster including a new leather piston seal) or is this a job for an "expert" rebuilder?
    Does anyone have any clues on what actually might be damaged?
    Will a master cylinder rebuild take care of the short pedal movement? Btw: wheel cylinders work well and brake hoses at front wheels were replaced to exclude collapsed hoses from the equation.



Thank you for any hint,
Christian Aicher

[Grant Owen]

The internal Vacuum hose may have come off. They are an easy Booster to rebuild yourself , the last one I rebuilt I never used a kit make sure springs OK get rid of any corrosion & use Neets Feet oil.  Google or look at a Lincoln forum it is the same booster used on 57 Lincolns. Most of the so called Professionally rebuilt boosters I have seen never seem to work that well & have problems they use the wrong size Vacuum hose or make the hose  to short & they never seem to get rid of the corrosion which causes drag so the booster never works properly.