Hello all. Today, I started changing my rear brakes. I put the system in the "fitting position" under the service menu & then took the caliper off. When I did, the piston extended fully... Once it did that, the screen went to "currently unavailable". There is no pressure/fluid in the piston, yet it will not retract under pressure. Any idea what to do? It cannot fit back over the old brake pads. Is there a way to trick the system into the fitting position? Perhaps my caliper is bad?

Edit: Went to the C43 forum and this is pretty common. Dealers have said faulty caliper. I don't believe so. A guy used a big C Clamp to push it back.

 

Glad you posted since I have rear brakes coming up soon. I wonder, did the electronic parking brake motor push the piston out?

 

If it is still in 'fitting position" you should be able to push it back in. You may have to crack the bleeder a bit but then you will have to bleed the caliper when you are done. You could try prying up the dust boot around the piston and see if there is corrosion on the piston that is causing it to hang up Have you tried with a C Clap or a brake caliper tool?

 

It took itself out of fitting position & fully extended the piston, mechanically. It's difficult to use a standard C-clamp as the bottom of the caliper has the plastic module for the (I assume) parking brake. Someone on the other forum said a piston compressor can put enough pressure on the piston to fool it into allowing fitting position to be reached. Theoretically, once back in that mode, I can easily compress the piston all the way & finish the pad replacement.

 

When ordering brake pads, make sure they are the actual ones for your car. I ordered 2 oem sets claiming to fit mine and didn't. I got the correct ones from FCP Euro

https://www.fcpeuro.com/products/mer...mer-0084200820

I was still on the original rear pads 54,000 miles later lol.

 

Update: I used a C clamp to apply pressure on the piston and it did get back into "fitting position". That being said, I only could move it a little bit... There is still heavy resistance & I'm worried heavy force could crack the plastic bottom. I'm going to take it out of fitting mode & then put it back in fitting mode again. Annoyingly, the piston seal ripped a tiny bit so I will have to replace it.