With truck in idle, depress brake pedal and engine seems to bog down, makes sucking noise in cab, no power assist with braking. Did not see any cracks in check valve or hose to engine. Did not notice any noise indicating leak in vacuum line to brake booster. Could this be a bad check valve? Any help appreciated.
Most likely a bad leak inside the brake booster itself. These leaks are funny, that they can only open the leak when the pedal is activated. It’s a fairly common failure, though. Replacing the brake booster is the only fix.
I agree with Beads. A check valve only prevents backpressure into the booster canister. When there’s vacuum on the system, the check valve is wide open. The sucking noise has to be coming from a leak past the diaphragm, inside the unit.
Thanks for the advice. I expected it but hope springs eternal. Guess I’ll have something to do this Saturday.