Shut the truck off, pump the brake until the pedal is hard, hold pressure to the pedal and start the truck, the pedal should sink a bit, if it does, the booster is working, if not the booster needs replacing, or the check valve, to test the valve remove it and try sucking thru both ends, it should work in only one direction. Also, the hose itself should be inspected for cracks.
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Monday, March 15th, 2021 AT 11:16 AM