View single post by Mark Rosenbaum
 Posted: 07-29-2006 01:21 pm
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Mark Rosenbaum

Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
The "pressure differential switch" (actually "pressure differential warning actuator" or PDWA) doesn't shut off brake fluid in event of leaks.  All it does is to close an electrical switch that allows the dash warning light to illuminate, in the event that a gross pressure differential between the front and rear brake circuits should occur.  Even if the PDWA's interior were gutted, all that would do is create a direct connection between the front and rear brake circuits, which shouldn't cause the problem you describe.

You might try disconnecting the vacuum line to the brake booster (and capping off the manifold port), then seeing if the problem changes in some way.  If so, it may be that you have some sort of defect in the booster.  Otherwise, all I can suggest is to do a thorough visual examination of the brake mechanisms on all four wheels, in the perhaps vain hope of finding something out of sorts mechanically: incorrect assembly, wrong or loose hardware, worn pins, weak springs, sticking pistons, etc.  If this exam does not provide any clues, then most likely there's something screwy in the hydraulic part of the system, but other than a slightly leaky master cylinder piston, leaking tipping valve, I can't imagine what the problem might be.

If all else fails then perhaps it would make sense to take the car to a good brake shop and let them sort things out.