Mercedes EPB's

Well I must admit I'd never seen anything like it! Yesterday we had a Mercedes C class in for rear brake pads. The young lad was just starting to do the job when I said let me put the scanner on first and set the EPB system so you can wind back the pistons in the calipers, okay, so I put the scanner on VERDICT D7, the software communicates and recongnises the car and accepts it. I look through the menus and come to the braking system. I select the option for winding back the calipers but then the scanner comes back with something like, this function is part of the ESP system and cannot be performed? So I'm searching through the software when a loud voice comes across saying HOW LONG DOES IT TAKE TO WIND BACK CALIPERS! I told the boss as long as the scanner takes to do the job.

It turns out the scanner could not perform the required tasks. The customer was asked to return today. The boss then puts his scanners on and neither could wind back the calipers. Then the boss says he can do them through the dash. After a couple of minutes he says they are done. I proceed myself to remove the brake calipers and wind the pistons back in. The pistons wind in anti-clockwise, so the nearside rear caliper is wound in fully and I go to the offside and wind that piston in but for some reason it didn't seen to go fully home. I advised the boss who like a bull in a china shop jumped back in the car and started to reajust the calipers again without waiting and asking me for advice first. So now both calipers are off and no brake pads in the carriers. As he's playing around in the car and nobody is properly aware of what he is doing, both calipers wind out fully beyond their limits! Oh dear! I then had to remove the calipers fully off the hydraulic system and put them on the bench and see if I could wind the calipers back after removing the motors. On the nearside caliper after removing the motor you can use an E socket to turn the spline and while turning the E spline using your other hands fingers and thumb you can push back into the caliper the piston, which should slide in nice and easy.

When I came to do the same on the drivers side, the piston went back in but didn't seem to go fully home. The brake pads would not quite allow the caliper to be refitted. DO NOT try and force the caliper back on. I decided to look more into the reason why the piston would not go fully home. After removing the motor and using the E socket to try and get the piston to go home, for some reason I could not do it. Now before I tried the first time the piston had almost if not fully but held inplace by the dust seal had really more than likely fallen out the bore. I decided to remove the piston and start a fresh.

I've never seen this design in my life! No brake fluid was observed in the piston chamber, but inside the piston itself when I looked inside loads of little ball bearings and long springs were in there. I looked inside the caliper housing and saw another spring coming out the wall where the caliper piston slides into the bore! To date I've no idea what that is all about?

Tomorrow I have to reassemble the caliper so that it can go back as an exchange unit! I hope I know what I'm doing!

I'll upload a couple of photos of the assembly tomorrow...