engine RPM climb, brake pedal sticks to floor..

Guys I need some opinions on a strange problem.

A friend of mine is trying to get my RC finished up, and today after getting the engine fired, when he depressed the brake pedal the engine RPM climbed, and the brake pedal stayed on the floor.

As soon as the motor was turned off the pedal "popped" back up. It was like some sort of vacuum was holding it down, but not giving any "feel" to the pedal.

The master cylinder is new, the booster is new. The brakes were recently replaced, new lines installed. and lines were bled. No leaks, etc.

With the engine turned off, there is great pedal and the brakes feel normal. When the engine is running the pedal is soft, no resistance, and stays stuck to the floor. As soon as the engine is shut off it literally pops back up, and acts normal.

Could this be a proportioning issue, or some sort of in-line valve that is getting stuck?

Is this booster related? Seems odd a brand new booster would act this way.

what ever it is I hope it is an easy and inexpensive repair. I have struggled going on 3 years now to get this thing back on the road.

I wish I had a manual brake setup for it, then I could eliminate the engine and vacuum. from the equation.

What about the inline check valve?

I haven't a clue, but sounds vacuum related to me. Mostly cause you say it works right when the motor is not running. Try unhooking the booster with the engine running, just to see what happens. New stuff can be bad sometimes.

"power brakes problem" By Hot Rod Dave. Have a look at this thread. It's right here on this page. Seems he has the same problem, only his is just started.

Split the M/C from the booster & check the clearance between the bottom of the "thimble" recess in the back of the piston to the rounded nub on the end of the pushrod, want ~1/8".

Hey Robert, that is great info. I am getting ready to install both master and booster and couldn't get a straight answer on this.
Thank You.

Quote:

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Split the M/C from the booster & check the clearance between the bottom of the "thimble" recess in the back of the piston to the rounded nub on the end of the pushrod, want ~1/8".

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And what does this tell me if it doesn't measure 1/8", Bob? Is the pedal overextending or depressing to far? Seems to me like the booster is becoming a vacuum. When the pedal sticks after dressing it, why does the engine jump in RPM's? If the booster is sucking, wouldn't this cause the engine to be put under a load? I am at a loss.

Vinny