Packard Forum Index » V-8 (1955-56)

im sure that this topic has come up before,but i have a 56 clipper with a rebuilt treadle vac and noticed the pedal will kind of pulse like its being pulled down buy itself and then the pedal will not come back up unless you pull it back up.

There is a large spring inside the vacuum section which is supposed to keep the pedal up.

With engine off, pedal will move down a little before getting hard but should return all the way back when you take your foot off. Do you feel the spring pushing the pedal back up? If so, but not with engine running then the vacuum section needs checking. There are some rubber valves which may have deteriorated.

If no return in either condition, the spring may have broken, retaining clip might have moved out of position causing a bind, or the piston may be gummed from dry or improper lube or brake fluid.

A known issue is brake fluid might have leaked past the piston shaft seal and congealed in the vacuum section. There is a gasket issue which can allow the fluid to be drawn into the vacuum side instead of returning to reservoir in case of a leak.

i can feel the pedal return when the car is off,but when running you can see the pedal being sucked down when you barely push on the pedal and then will stay down.i noticed when the pedal is down i can just tap on it and it will come back up.the whole unit was rebuilt about 8 months ago this is the first time i am able to drive the car.thanks wes

Not sure how much time the typical rebuilders spend inside the vacuum piston section since it's generally reliable. Suspect cleaning the can and lubing the power piston leather seal is about it. The majority of time and parts are undoubtedly spent on the hydraulic section where problems usually are found.

I think a consultation with Ross or one of our other mechanics on site known to be familiar with the vacuum side would be a good idea. Maybe something simple or maybe in need of a thorough rebuild of that section.

Either the poppet valves in the vacuum section are leaking, or one of the return springs has broken/ bent. Possibly the vent hole in the reaction diaphragm is plugged. Anyway, the vac piston assy needs to be gone through.

i noticed that there is no check valve in the vacuum hose like a typical brake booster today,so i added one and it seems to soved the problem.the pedal no longer stays down and the fludder is gone.thanks to all that replied.wes

Waddya mean - NO CHECK VALVE??
There is one at the rear of the carb where the hose for the TV attaches. Or are you speaking of some other vacuum hose??

nope no check valve,just a fitting that the hose attaches to for the booster.i have the 2 barrel carb so it may be different from a four barrel

It needs the check valve. Consult the manual. Put the check valve in and try it. PRobably won't solve the problem but the check valve needs to be there anyway.

If you haven't already you might want to visit this excellent production by Ross Miller.

packardinfo.com/xoops/html/modules/article/view.article.php?c8/404

The check valve is the same whether you have a 2-bbl, a 4-bbl, or 2x4 bbls. Need a picture of it?