hanktohendrix

Hi everyone,

when I disconnect the vacuum hose from intake manifold to brake booster on manifold side, I can not evacuate the booster on 'natural way': sucking with my mouth on the hose feels like a leaking booster.
Well, if the hose is connected, the booster is working fine - engine is running fine too.
If the hose is closed with a plug I have no brake-assistance (pretty normal) and engine is running without any influence. So the booster seems to be "tight".
But I can't evacuate booster with my mouth.
That's why I'm a bit confused
How is it with your booster?
Is the "leak" normal if you check it on engine stopped with little negative pressure?

Thanks!
Markus

lakebumm

The brake booster is a pretty large volume to draw a vacuum on by just sucking on it.

Find a vacuum pump and try that. When I checked a C3 booster with a hand vacuum pump, it took alot of pumps just to get a little bit of vacuum.

Good luck

BILL

856666

Hi Markus,

Brake boosters are very reliable, they seldom go bad, but if one does go bad the standard complaint is the pedal feels hard when the engine is running - (no assist)

Booster test: when you shut off your engine you should get 2 - 4 pumps of the pedal before it gets difficult to push / hard. If it immediately gets hard to push the booster is bad or the check valve connecting the booster to the hose is bad.
Otherwise your booster is good
Phil

Frankie the Fink

The three classic booster checks are to remove the plastic valve and make sure it only works one way by sucking on it; reinstall the valve if good; then;

Put your foot on the brake pedal with the engine off and then start the car - the pedal should drop about an inch when the booster takes hold; then;

Do the test just above from Phil - this shows the booster is holding a vacuum reserve....this gives you some minimal boosted braking if your car shuts off while driving to get you to safety.

A final check is to make sure the car's idle does NOT drop when the brakes are applied hard - if it does you have a subtle leak somewhere - may be even on the back of the booster where there is a filtering device for atmospheric air.

hanktohendrix

Thanks!

In fact my booster doesn't hold the vacuum for a long time after engine stopp - if I have it right in mind, the pedal gets hard immediately :-(
But brake assistance is pretty fine.
If I close the hose, it has no influence to idle at all.

All in all I'm afraid I need a new booster...

BTW: What's the job of the plastic valve? Just ensure one way flow?

Markus

Frankie the Fink

Exactly !

Check the prices on boosters carefully - many vendors offer the booster, complete with a new master cylinder, for just a few dollars more than the price of the booster by itself....