Brake pedal pressure

[Kellerbear]

When I first start my '78 Avanti II, and depress the brake pedal,I hear a hissing like air escaping. The pedal won't go down very far and brakes are not grippy at all, like there's no power assist. Then after it's warmed up and touch brake pedal, no hissing and brakes work fine.

Any suggestions on what's up?

Thanks,

Tim

[ernier]

I have to think it's a problem in the booster. But a simple experiment would be to replace the check valve and to check or replace the hose and see what happens. The hose must be booster hose, gas hose will collapse.

Your pedal is hard because you have no vacuum built up in the booster.

More than likely you need to replace or rebuild the booster.

ErnieR

When I first start my '78 Avanti II, and depress the brake pedal,I hear a hissing like air escaping. The pedal won't go down very far and brakes are not grippy at all, like there's no power assist. Then after it's warmed up and touch brake pedal, no hissing and brakes work fine.

Any suggestions on what's up?

Thanks,

Tim

[Gunslinger]

Another test is, while the engine is idling, remove the big vacuum hose off the booster...if the idle speeds up dramatically, your booster may be OK. If the idle stays the same you have a bad booster with a big internal leak.

From your description, it does sound like a bad booster.

[WayneC]

...while the engine is idling, remove the big vacuum hose off the booster...

Gunslinger, I think you mean remove it and plug the removed end of the hose, don't you?

[Gunslinger]

You're correct...I forgot that little part!

[Kellerbear]

Thanks, all. I notice when I depress the brake pedal first thing on start up, the RPMs jump. Doesn't seem to happen when it's warmed up. Again, many thanks.