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Old 09-27-2012, 07:05 PM
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cobalt327 cobalt327 is offline
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Originally Posted by vetteman View Post
I have a 57,3100 chev pickup with a CPP firewall mount P/B kit. After two different boosters, from them,problem still remains. Brake pedal will not return last 1/4"-1/2" or so. Brakes bind. With vacuum disconnected,driving vehicle, brake pedal returns completely and firmly. Everything is new,no binding anywhere, pedal has return spring,etc. Booster pin is adjusted with a gauge. All the usual areas to check/confirm have been done. Brake system works great otherwise. I am convinced it's a cheap overseas booster that's the problem. CPP believes otherwise. I get, "there's nothing about a booster that could cause this". Well, then why does the pedal return VERY good with out vacuum applied, while idling/driving vehicle? Am I missing something here?

Talked to a booster rebuild shop, and they said definitely a booster issue.Maybe they said that in order to sell me a booster, but I'll give them the benefit of the doubt for now. Any thoughts?

Was looking at MBM brake boosters. USA made? Got to get this bullcrap resolved.
For them to say there's nothing within the booster that could cause this is ludicrous.

There's a valve that seals the side of the booster nearest the pedal so there's vacuum on BOTH sides of the diaphragm when the brake pedal is not applied. This valve opens when the brake pedal is depressed, which allows atmospheric pressure to enter the pedal side of the booster, allowing the vacuum on the master cylinder side to help apply pressure to the MC.

If this valve isn't sealing the pedal side when the brake pedal isn't depressed, the vacuum on the MC side of the diaphragm will pull the pedal downward.

Here's an interactive representation of a vacuum operated power brake booster.

Last edited by cobalt327; 09-27-2012 at 07:22 PM.
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