I have an '87 560 SL and last year had a complete brake job done, Recently I went to drive the car when I notice the brake pedal didn't return to the up position when I let up on the pedal and shortly afterwards I started hearing a hissing sound like air coming out of a hose. Is this some kind of vacuum leak? Any ideas or suggestions?

 

There is a spring to return the pedal. The hiss could be the diaphragm in the power brake booster ruptured. Where is the vacuum/economy gauge needle when the car is running?

 

Thanks, I'll check out the spring and the hissing sound.

 

I checked the economy gauge and it read zero or economy, when I would rev up the engine it would make a slight movement and then settle back to a zero level.

As it turned out the brake pedal returned on its own after several brake tests.