Hey there,

Thanks for taking the time to check this out. As the title says- Rear brake caliper pushed itself out. My kids were around, something messed up.

First off I have done many brake changes before. Not only on this and other Mercedes, but bmws, and other cars as well.. This was carelessness mixed with idle time and a pinch of momentary stupidity.

So the piston over extended and popped out loose into the boot - and then came out releasing brake fluid everywhere. When I discovered this I was upset - but not panicked.
Everything is as you would expect except there are several springs and tiny little steel ***** (small bearings) inside the fluid and inside the boot area (unexpected to me). I clean up the area and gather all internal components with a magnet. After cleaning everything up and getting a better look I can understand how the piston and electronic parking brake interwork. There are several springs and around 60 small ***** in total. The bearings allow the parking brake actuator to go in and out- locking the parking brake at whatever depth the brake is extended too. They are held into spiraled grooves using only the pressure from each other, the tension from the springs, the grooves and the opposing walls of the shaft to hold the ***** in place while it winds in and out.
I quickly made up a system to put all the bearings in place with the springs and feel pretty good about it. This will be my first time rebuilding a caliper with electronic parking brake.

I am confident I can get this thing reassembled. I am also pretty confident I can get the air out of the line. ( though I am curious how much everyone thinks got into the system. the brakes have not been pushed or used since....and its the rear passenger wheel which is where I would start my bleed anyway...)

I was just wondering if anyone else has any experience with something like this? A parts diagram for the inside of the caliper would help but not necessary. When I look it up, it just shows the number for the whole caliper minus the electric parking brake motor.


What I am concerned about is the electronic side of this.
What issues should I expect to come from this? What are some things to make sure I check, set, test, or anything before I restart and move the car?
Right now the parking brake is activated, so one side is locked in park...When I reset the electronic parking brake inside the piston and reinsert it into the caliper- this side will be all the way retracted and the drivers side will be in extended/locked position.
Will it reset when I put it into service mode and retract?

Any and all help or advice is welcome. I am really trying to tackle this myself- I am sorry if this comes across as a fools task.
Thank you for any and all help!
Please try not to be too negative...- I feel dumb enough as it is!

Thank you all very very much! Hope you are having a great day!

-Runninginthe90s

P.S.- I can post pictures if anyone else would like to see anything or if it helps figure this thing out!