1992 Plymouth Voyager Very heard to depress the brake pedal

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Brakes problem
1992 Plymouth Voyager 6 cyl Front Wheel Drive Automatic 140000 miles

Driving the vehicle home one day I found that it was increasing harder to stop. I had to really apply a great deal of pedal pressure to get the van to stop. Since the problem I cleaned the driver side caliper bracket, (wire brushed clean) and replaced the pads. Verified caliper piston moved when depressing the brake. Passenger side cleaned mounts, replaced pads, and replaced caliper since I couldn't compress the cylinder into the caliper. After reassembling the breaks still tough to depress the brake pedal. I suspect the power assist is the problem. Is there a fuse for the pump that drives the power assist? Is there any way to narrow down the problem (i.E. Master cylinder assembly, power assist pump, cogged lines, etc).
Not sure how to proceed.
Thanks for any help you can provide.

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Wednesday, July 30th, 2008 AT 2:49 PM

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Lack of power assist may be due to low engine vacuum, a leaky vacuum hose or a defective booster. Sometimes a faulty check valve will allow vacuum to bleed out of the booster causing a hard pedal when the brakes are applied. This condition can be diagnosed by starting the engine (to build vacuum), shutting it off, waiting four or five minutes, then trying the brakes to see if there is power assist. No assist means a new check valve is needed.

A quick way to check the vacuum booster is to pump the brake pedal several times with the engine off to bleed off any vacuum that may still be in the unit. Then hold your foot on the pedal and start the engine. If the booster is working, the amount of effort required to hold the pedal should drop and the pedal itself may depress slightly. If nothing happens and the vacuum connections to the booster unit are okay, a new booster is needed (the vacuum hose should be replaced, too).

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Wednesday, July 30th, 2008 AT 2:55 PM

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