1992 940, 360k miles.

I noticed today that when I depress the brake pedal I hear a hissing sound. The pedal also feels kinda stiff.

When i shut the car off I hear a hissing sound and the brake pedal forces my foot up.

Car starts, idles and runs just fine.

Recently my boy replaced driver front caliper and both rubber brake lines up front. There is no brake warning light while car is running.

Think this is a bad brake booster?

 

or a bad vacuum one way valve on the hose from the manifold to the booster...

 

That's why I post questions to this forum...others think of things I don't.

Thanks pierce

 

So i ordered a Bosch check valve from fcp for less than $5...ipd sells the same part for almost $17. I had other items on that order and they shipped separately from the check valve...which was shipped from Portland...hhmmm.

Anyway...new check valve solved the problem.

Thanks again pierce.