"Nadeem" wrote: '94 Chevy S10
I posted a message stating the brake pedal lost tension briefly then went back to normal. The advice was that a brake pad sheared off or my master cylinder was failing.
Could have anything to do with the brake booster being connected to engine vacuum from the intake manifold. If the engine misfired or lost vacuum pressure would this affect the booster and cause the pedal to lose tension? ________________________________________________
The vacuum line from the engine to the brake booster has a safety check valve to keep booster vacuum from disappearing when the engine is shut off or quits. That is why you can still use your brakes once or twice after turning off the car.
It is possible for the check valve to fail but it is very rare.
An intermittently soft brake pedal is most probably a sign that the master cylinder is failing. Your liability depends on how fast and in what direction you are going when it fails.
Good luck.
Rodan.