Cosworth2000

Hey guys,

Anyone know how to fix this. While changing my rear brake pads, my caliper piston did not retract fully. I went back into the car to see if I had the setting correct (I did). When I existed the fitment to see if I could reset it and start again, the piston came almost all the way however it would not retract back into the caliper. The parking brake seems to work still on the other wheel without any problems, however the piston refused to retract back into the caliper and actually came out past the protective boot. I could feel like there are some gears inside the caliper that pull the caliper back for the fitment mode however it would not re-engage. I took the car to Mercedes whom is telling me that their tech can not push the piston back into the caliper (weird) however I need to purchase a new caliper to be installed.

Has anyone has this issue? Doe anyone know why a MB tech can't push the piston back into the caliper when in fact MB sells a piston/caliper rebuild kit online?

Thanks so much.

AMGiggity

Sorry man that sucks. Can't help you, probably a seized caliper.

I did my pads a few months ago but next time will not do it. A lot of hassle to not save much. Those wheels are damn heavy. I'll just buy the parts and take it to an independent tech.

RichardCranium3

If I'm reading your description correctly, I haven't heard of this before. Anyone I've seen comment on changing rear pads has commented the service menu command to retract the caliper works about 95% of the way, but everyone still had to further compress the piston a bit to clear the new pad and/or rotor, myself included. Sadly, no surprise the dealer wants to just charge you for a new caliper instead of figuring it out.

Cosworth2000

Yep, so the service guy contacted me an told me that the techs can not put the piston back in. I asked them about the Caliper Kit on there website that is for this part and he told me that even if they did try to use the kit, it could take 4 hours of work so it would be easier to purchase a new caliper. So I did this and now I'm waiting on the new caliper. I do find it weird that they sell a caliper kit however according to the service guy, the rear calipers can't be repaired if the piston comes all the way out.

I will keep everyone updated on this for those that are interested in this issue.

stockbmw

Sorry to hear that, but when you went back in the car, what settings did you perform?

Ignition on ACC and press phone+ok to access workshop menu?

​

Cosworth2000

Yes, that is the process.

stockbmw

Did both rear caliper pistons fail to retract or just one side?

I am thinking of making a makeshift 2x4 to shimmy in the calipers before doing this brake job.

AMGiggity

I'm a little confused, what is a "Caliper Kit" and why do you need it to push piston back in? Why not just use a C-clamp like this?

stockbmw

Probably because of poor engineering integrating electronic parking brake into rear caliper.

Not first time hearing failure because of design error.

z28lt1

I believe a poster on the forum with a C300 had a similar problem. Unfortunately, he only posted that it was a $1300 dollar dealer fix, so I assume new caliper plus dealer rip off labor to replace and bleed system, as that is a lot of money:

https://mbworld.org/forums/c-class-w...-function.html

Cosworth2000

Hello friends... for the C-Clamp question, you can't use a typical C-Clamp on the rear caliper as you will have to clamp on the automatic parking break casing. You have to use a caliper spreader tool which you'd also use on the front brakes.

So here is the end result.

I looked over the caliper design and noticed the following. From what I see the rear calipers on our cars "CAN NOT BE REBUILT". You can however rebuilt the front calipers as they are standard brake design without the electronic parts and the turning piston. The only recourse is to purchase a new caliper (or find on on line and DYI it yourself) if your piston comes all the way out, bleed the system because you have to take the old caliper off. I had a great service agent whom was able to give me a great deal but for those that want to know ... a new rear caliper (without the electronic parking brake attached) is $435 CAN.

I have learned something from this experience and may make a Youtube video to show people how to avoid this. I will be uploading a Youtube video to my channel to share with people what the caliper looks like and how the piston works however the design of this system (and I assume all the other luxury brands do the same), is a flaw as you can't rebuild it, it can fail and leave you stuck. I would assume that this will happen when these cars reach 10+ years.

AMGiggity

But I used the exact C-clamp you see in the picture on both rear calipers....? I put the car in service mode, removed the caliper, used that C-clamp to further push in the pistons because new pads were too thick to fit, placed the caliper back on the caliper carrier, and.... done. I still don't understand what went wrong in your case.

stockbmw

If I read his original post correctly, because service mode didn't retract the piston all the way, he went back into the car and performed again while caliper was off the rotors. When he did that, parking brakes activated but no where to clamp down and performing service mode was futile at this point but did it anyway.

RichardCranium3

Yeah the real issue was the second attempt at cycling the electronic retraction. Had he just compressed the piston by hand/clamp from where it was after the first retraction, he’d be on the road.

lala007

Hey. So I recently took my calipers off to get them powder coated. The person painting my calipers removed the pistons. Inside were bearings and springs. When I saw it I knew right away that it was ruined. Mercedes won’t sell me just the piston and bearings with pin. So I bought new calipers. Fml. Is there any news on rebuild kits??? Or anyone know how to take the piston off without damaging the bearings and springs?! Or, perhaps does anyone know if it’s okay to leave the piston on obviously covered when powder coating?Thanks

z28lt1

Don't know about the rebuild kit, but I can tell you some powdercoaters will leave the seals and pistons in place. The baking temps are lower than what most calipers would see on a race track (although for a longer time). I've spoken to some who refuse to work on them in any state but bare (I suspect for liability reasons), and others who have coated with seals and pistons in. If done properly the results seems to be just fine.

sneaks32

damn I do my brakes all time never heard of that issue. I repair them powder coat them. if its not retracting then the brake was forced back to place without releasing the hydrolic pressure to the caliper which will infact mess your master brake cylinder to go. or the brake mechanism is no good. try doing it manually. turn key on release the E-brake this should allow you to slightly. use a flat head to give you separation from the rotor and take it off now with a hex bit number 3 or 4 remove the electrical box that retracts. when you take off the screws carefully with a flat head simple pry under the screw holes little on each side at a time until you can pull it off don't need brut force. you'll find a torx screw that should be a 4 or 6 torx socket and go counter clockwise until it stops now place the cover back on and screw it back togehter make sure veto regrease the torx screw and grease the oring before putting the cover back on. put your brakes back together and now perform the retract sequence. and see if that fixes it.

lalu713

Hi All,

Read through this and am surprised the dealer would not rebuild your calipers, I just recently got my calipers powder coated. To reduce the cost of the powder coating I disassembled all 4 calipers. The trick for the rears is to place a two by four between the calipers and use compressed air to fully extract the piston but not letting it blow out. Once out you can easily rebuild the calipers, I purchased the rebuild kit online for the rears, new seals an all. It took my less than 1 hour to re assemble both rear calipers.

The rear motor assemble un bolts from the rear of the caliper with two tore screws, and the piston screw (for the e brake) is held in place with a c clip, leave this clip on while removing the piston. once piston is removed, you can then remove the c clip and remove the piston screw mechanism.

pjscrs2

Hey Folks,

i had the back caliper over extend on me as well. Thankfully there is an easy solution.

1) use a c clamp carefully push to piston in till it rests against the extended internal parking brake screw. Push on the center.

2) Now the dash control will let you go to the retracted service position.

3). Use the c clamp again to push the piston all the way in.

4) replace pads and put back together. Use dash menu to put parking drake in operating position. All good now.

Dealer as usual is full of it. Easy fix!!

Paul.

Sean._.S

Exact same thing has happened on my S550, though I did not exit the fitting position myself, the car apparently did. I wonder how long a new caliper will take... Let alone how expensive.
Edit: I will try the C Clamp method pjscrs2 used^

Sean._.S

How much pressure did you have to apply? Usually, I can retract pistons with simple leverage (almost equating to that of a C- Clamp) however, this one does not budge. What kind of C clamp did you use that wouldn't damage the plastic module on the bottom?

pjscrs2

You only need to apply enough pressure to move the piston back so the end of stroke sensor is satisfied. It's only a small amount. Then, using the dash control, it will now allow you to retract the parking brake. Once retracted, you can then push the piston all the way back with the C clamp. I used a large 10-12" C clamp. The issue is that the piston will extend a bit too far when using the dash extension function. It just needs to be put back a little bit manually with the c clamp, then it will allow the software to retract it completely. There is certainly no reason to replace it. It only over extends a small bit and this is well within its travel.

Sean._.S

Thank you so much man. The W222 forum is pretty useless when it comes to this as most don't work on their own cars. Will try this tomorrow.

Chamelleon

Hi everyone,

While doing rear rotor and brake pads replacement on my ML W166 350, I’ve got stuck in a situation when my left rear caliper piston is not retracting and I can’t push it down to get enough space for the pads. Btw, yes, I put the car in service mode according to the manual.

I’ve tried different options and I have one more to try but order to apply straight force on the piston I need to remove the black cover from the caliper.

Did anyone removed the retracting mechanism?
Maybe it will help me to push the piston down.

Does anybody know how to remove it?

JDMAP1

here it is my friend

https://mbworld.org/forums/m-class-w...ake-pad-2.html