Compression Ignition Addict
Join Date: Aug 2008
Location: Madison, WI
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Vacuum pump issue usually results in a too-hard pedal (not enough vacuum boost), not too-soft.
Try this - truck in Park, rev it up to keep the vacuum pump pumping, pump the brake five or six times. If the pedal firms up, that suggests (but doesn't prove conclusively) an internal failure of the master cylinder.
Have you visually inspected all the lines, and the calipers and rear cylinders, for brake fluid wetness? Can we presume that the reservoir fluid level isn't crazy low?
If you don't see any external leaks, and the fluid is full, the next thing to try is simply to bleed the brakes. Start with the right-rear (furthest from the M/C), then left-rear, etc.
Belt noise - remove the belt and spin each driven pulley (A/C, P/S, alternator, vacuum pump, water pump, tensioner, both idlers) by hand. The water pump and P/S pump will normally provide some resistance, and the vacuum pump will provide a bit (it should sorta "puff"), but none should be noisy, or loose.