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treadle vac brake booster

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  • Brakes: treadle vac brake booster

    I realize that this is not a Packard forum, but I'm hoping someone has experience with the treadle vac used on 55-56 Packards. I installed a repair kit in my 56 Packard system to try repair a hard pedal problem, but it made no difference. I have good engine vacuum, and before reinstalling brake lines, the pedal would depress fine. Once I installed the lines, the pedal is hard and only depresses about 1/4-1/2 inch, then becomes solid. Brakes work and stop the car, but if I hit them hard they almost put me through the windshield. Obviously I missed something as there seems to be no vacuum assist. Before I start tearing the unit apart again and not knowing what to look for, I hope someone can give me an idea of what the problem may be. Thanks.

  • #2
    First make sure that vacuum is getting down to the unit. Often times the check valve at the back of the carburetor is stuck shut and won't let the vac. build.

    The usual overhaul kits do not address the vacuum piston in the unit. You can remove the vacuum piston without removing the whole unit from the car with bit of fiddling and that will save you bleeding the brakes etc again. Once you have the vac piston in hand first make sure that the center plunger is not frozen in the housing. After that it is a matter of dismantling it and making sure that the two poppet valves move and still have their little rubber discs on them. When you step on the pedal, one should close and then the other one opens. Typically if the braking action is very abrupt on those cars it is because of failing rubber on the poppet valves, ie deeply indented. The other and more seldom cause of poor action is failure of the reaction diaphragm sandwiched between the two casting halves, Finally, the leather piston seal needs to be soft and flexible enough to seal against the vacuum can. Be sure to oil the wick behind the leather lip.

    You might want to hang out on the excellent website for other Packard questions.


    • #3
      Thanks Ross. Will check out your suggestions.