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?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

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.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

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.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Thanks for the input.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles