I've had a high mileage (157k) 2004 E55 for 2.5 years now, and it has always had a lot of travel on the brake pedal, but recently it seems to have gotten worse. The car brakes fine, and when I press hard on the pedal, the car will lock up fine.

Do these cars naturally have a lot of brake pedal travel? Besides potential air in the lines, could a lot of pedal travel indicate a worn brake pedal?

Thanks for any input.

lots of pedal travel would indicate air in your system. Pedal thickness should not play a factor as the amount of fluid displaced will be absorbed through the excess brake fluid in your reservoir. Air compresses with pressure, fluid does not.

Check for codes, check fluid level and have the system properly bled and see how that goes.

The SBC system in the W211 uses a mechanical feedback electrically actuated brake system. You can have significant amounts of air in the system and the pedal travel is not affected. Thus the importance of proper maintenance.

In your case, it could be the "master cylinder". Either the spring or the rubber biscuit are worn out. See attached for functionality. This is *not* like the old-style hydraulic systems.

Thanks for helpful replies.

The brakes in my '06 do feel "softer", but they work fine once you get used to them. It's that way even after a major service that replaced the brake fluid.

When I was given a loaner by the MB dealer, I kept jerking to a stop in their parking lot as I got used to the more sensitive brake pedal of the '16 E350.

Thanks for this info. I've been wondering how the electro-mechanical interface works on the SBC. I have very spongy brakes that take a lot of travel before they "bite". New pads and rotors (along with a fluid change) are on the way, but I was wondering if the "master cylinder" could be affecting my brake feel.

Do you have a part number for it? Has anyone ever replaced this piece and gotten better brake feel from it?

Bumping this thread, curious if anyone else has replaced a master cylinder on higher mileage (156k for me) E55s and seen an improvement in feel.

I always just accepted the pedal travel and feel as a result of the SBC system, and have never driven another SBC car to compare. The reason I bring it up is after a recent alignment, the well-rated independent Mercedes tech and shop who did it mentioned that the pedal felt far too soft. 'It's an AMG, it should have an aggressive and firm feel' and I'd like to think they see other SBC cars in there.

I've did a flush last year using STAR, and it all went as it should. It had the SBC unit replaced 3 years ago under warranty, and I also installed the damper on the line when I did the flush to help with the off-pedal vibration (which it did). The only thing that might be helpful to note - when I finished the flush, STAR has you go through different 'levels' of putting pressure on the pedal and holding it in place for a set amount of time. The first time I did it, when I got to the last one, it didn't hold long enough and it made me go through the pressure tests a second time. It passed the test for air in the lines too. Could this be indicative of a worn master cylinder?

I know there really isn't any other way to check the wear on one, just curious if others have replaced it and seen an improvement.