E420 Brake Pedal Sinks on Startup
 

I have a friend with a 92 500E and he is having a noticeable problem with his brake pedal sinking significantly toward the floor as he starts the car. Maybe it is just the power of suggestion, by I noticed that mine is also sinking on startup. I suspect it has something to do with vacuum, but is some sinking normal (of course, I'm pressing on the brake when I start the engine). What could cause this to occur? Any ideas?

Don't concern yourself if the brakes otherwise function properly---it's normal. Mark

They haven't shown any sign of not working. I am just curious now why the pedal sinks when the engine is started. Given the combination of electric charge pumps and return pumps, it's hard for me to tell. I've read somewhere that the vacuum is not even the primary mode for power assist on this car.

Call me crazy but I'm going to guess that your brake pedal is sinking because you're stepping on it ;)


In all seriousness, most if not all of my cars have done this at startup.

Totally normal. When the car is not running, the pedal should be hard to press down.

Thanks for the input.