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Old January 27th, 2013, 12:44 AM
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Cayoterun Cayoterun is offline
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Join Date: Jan 2013
Location: Guymon, Ok.
Truck: GMC V12 powered '46 Chevy pu
Age: 84
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Default Brake fluid lose thru booster?

On Thumper's truck, I'm using '84 GMC brake booster and master cylinder.
The booster vacuum line is run to manifold vacuum at base of carb.
The master cylinder is a new/rebuilt.

Problem: The brakes work great. But somehow, after driving the truck a short time, it will draw the brake fluid from the small compartment (rear) of the master cylinder back thru the booster vacuum line to the manifold.
Front compartment, (large), stays full.

Is the master cylinder bad, or is the booster messed up. I used the booster from the donor truck, and know no history on it.

I used General discussion as I didn't see a brake sub-forum here yet.

Any help appreciated,
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Cayoterun
Okla Panhandle

I think I'll fix it myself, and pay the extra $500.
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