Unusual brake problem.....Need help
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
Unusual brake problem.....Need help
So here is the problem....When the car is turned off, the brakes feel nice and firm. When I turn the car one, the brakes feel spongy. I also tried disconnecting the vaccuum hose to the brake power booster then started the car again. Brakes felt fine.
Could the power booster be getting too much vaccuum somehow and there fore making the brakes feel spongy? (Probably not likley ut I am brainstorming) How about a booster failure?
I have recently replace the master cylinder, prop valve, calipers (o-ring caalipers from VBP), brake lines, rotors and pads so everything there should be fine. I have also bled the brakes ad nauseum and I am 99.99% sure there is not a drop of air in those things. Like I said, when the car is turned off (or when on but vaccum to boost is disconnected) the brakes feel nice and firm. When I run the car WITH the vaccum to the booster connected, they feel spongy again.
What the heck could this be?!?!?!?!
Thanks
Shane
Could the power booster be getting too much vaccuum somehow and there fore making the brakes feel spongy? (Probably not likley ut I am brainstorming) How about a booster failure?
I have recently replace the master cylinder, prop valve, calipers (o-ring caalipers from VBP), brake lines, rotors and pads so everything there should be fine. I have also bled the brakes ad nauseum and I am 99.99% sure there is not a drop of air in those things. Like I said, when the car is turned off (or when on but vaccum to boost is disconnected) the brakes feel nice and firm. When I run the car WITH the vaccum to the booster connected, they feel spongy again.
What the heck could this be?!?!?!?!
Thanks
Shane
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
Originally Posted by ShaneLU97
Brakes felt fine.
Could the power booster be getting too much vaccuum somehow and there fore making the brakes feel spongy? Shane
Could the power booster be getting too much vaccuum somehow and there fore making the brakes feel spongy? Shane
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
If they stop your car, then there's nothing wrong. That's the way power brakes are in all cars.
Try this - with engine off, pump up brakes...they are hard, right? Then turn on engine. The pedal will go another 1/2 inch or more as the vacuum comes on.
Try this - with engine off, pump up brakes...they are hard, right? Then turn on engine. The pedal will go another 1/2 inch or more as the vacuum comes on.
Melting Slicks
Joined: Jan 2003
Posts: 2,817
Likes: 21
From: Somerset, NJ
Power disc brakes feel differently when the engine is running unlike manual disc brakes that feel the same either way. I know on manual brakes if the adjustment rod going into the back of the master cylinder piston is out of adjustment you will have some play when pressing on the pedal before the brakes grab. Sometimes the rods locking nut under the dash will loosen and the rod will move out of adjustment. This already has happened to me years ago on my 73' and it is a pain to get a wrench up there to tighten that nut. There may be an adjustment on power disc but I'm not sure. Maybe someone else can weigh in on this.
Usually when a power booster goes bad the pedal will feel hard also with the engine running and you will hear the sound of air escaping when pressing down on the pedal.
Usually when a power booster goes bad the pedal will feel hard also with the engine running and you will hear the sound of air escaping when pressing down on the pedal.
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C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
Likes: 2
From: Twin Cities Minnesota
Power brakes always feel spongy as far as I'm concerned...
But it sounds like you may be missing you check valve which will keep vacuum in the booster Making the brakes always feel spongy
But it sounds like you may be missing you check valve which will keep vacuum in the booster Making the brakes always feel spongy
