Brakes: Idle changes when using the power brakes

[Orestudeguy]

I thought Scott might ask about this since it is his car. He hasn't, so I will.
The car is a 1966 Cruiser with power brakes and a V/8 engine.
When pressing down on the brakes the idle (when in park) will increase. Scott has mentioned that when he comes to a stop sign it will also cause the engine to rev up a bit.
None of my Studebakers have power brakes and my experience with other makes has me thinking that the booster may be bad. Scott has also mentioned at times the brakes have been "touchy" a bit hard then will grab.
I have checked the fittings and hose and all seems to be in good shape with no vacumn loss.
Am I correct in thinking the booster may be in need of a rebuild?

[bige]

Most probably a booster issue.

ErnieR

[BobPalma]

Yep. There's an internal vacuum leak that is allowing the engine to receive more air when the brakes are applied; hence, the idle speed changes. BP

[Orestudeguy]

Thanks guys,

Now to tell Scott that there is another thing to ad to his list of "things to do" with this car.
We have made some progress thou. The car starts right up and idles like it should. Scott got the exhaust system welded up (it was in several pieces before)
He still don't like the sound thou, someone put a "Flowmaster" and it's a bit loud to his liking. New muffler is added to the list.
The transmission linkage issue has been fixed and the car now goes into park.
The alternator will be back tommorow afternoon (bad bearings) from the rebuilder.
We now have the correct ignition switch (still have to install) and some door lock cylinders. Also some of the loose dangling weatherstrip has been reglued to the car.
And we now have the correct transmission dipstick and tube ( to be installed soon).

The annoying thing that bugs me is that even thou I have this car tuned to where it will start on the first revolution of the engine, it still has a miss. I have replaced the plugs, wires,
cap and rotor. but I still feel a miss. Going to start pulling wires and hopefully I'll find what cylinder it is.

[BobPalma]

George: Don't pursue curing the miss until you have temoporarily, at least, removed the vacuum hose to the power brake booster at the manifold and installed a good pipe plug there.

That will eliminate any question as to even a vacuum leak at idle without the brakes applied.

Because of the manifold runners being arranged as they are, you could be trying to tune a car that has a variance in air/fuel ratio among the cylinders. It will never tune to run smooth if that's the case. BP

[Orestudeguy]

Bob,
Thank you. Good idea. I will plug off the intake and eliminate the booster then pursue the miss, that is if it's till there.
Thanks