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Unable to Fit New Rear Pads & Rotors on '15 ML 400
2015 ML 400 (4JG 166, with 276.8 motor)
Vehicle requires new rear brake pads and rotors. Vehicle is equipped with electric rear parking brakes. Positioned the parking brakes as per WIS and successfully removed the rear pads and rotors, without a problem.
However, the caliper's piston has not retracted a sufficient distance to allow for the increased thickness of the new pads and rotors. (This is only on the right side; haven't attempted the left side as of yet.) Have subsequently repeatedly commanded repositioning of the parking brakes using the vehicle's onboard control system as well as by use of an independent scan tool but am unable to compress the caliper piston a sufficient distance to allow for installation of the new hardware.
Can the caliper's piston be repositioned mechanically inward by use of a brake caliper compression tool that would displace the piston directly into the caliper ... or should the piston be reseated by use of a caliper tool set that slowly rotates (clockwise?) the caliper inward?
An SDI fault code check reveals no active, stored or pending fault codes in the electric parking brake system.
The parking brake is what retracts. You have to use a piston spreader to force the pistons back to the furthest point so you can install the pads. I use this one.
I have the Mercedes branded version of the following piston press tool but was unable to achieve any inward displacement of the piston into the caliper. Was uncertain if a rotary displacement of the piston was required to reseat it, in lieu of fore/aft displacement within the piston's bore.
Also attempted to move the piston with the caliper's bleeder valve opened; brake fluid did exit the caliper but, again, no movement was noted in the piston. Tried pressure bleeding the rear right brake fluid hydraulic circuit; was able to obtain brake fluid from the caliper's bleeder valve but, again, no piston movement. Caliper faulty?? Vehicle shows no sign of abnormal pad wear; has 120K miles and received brake fluid renewal every 20K miles, since new.
Pressurized rear hydraulic circuit to 10 PSI using a pressure bleeder and then, with the caliper bleeder valve open, applied compressive force on the piston using the above listed piston press tool. After a few seconds of increasing pressure, piston gave way and slowly receded into the caliper. Was then able to install the new brake pad set, in conjunction with a new brake disc, with no further issue. Closed bleeder valve and exited assembly mode; caliper piston extended outward, fully taking up the existing slack between the brake pads and brake disc, when the brake pedal was depressed.
Successfully renewed brake pad set and rotor on fellow side, with no issue. Subsequently road tested vehicle; brake system was found to be fully operational.
Pressurized rear hydraulic circuit to 10 PSI using a pressure bleeder and then, with the caliper bleeder valve open, applied compressive force on the piston using the above listed piston press tool. After a few seconds of increasing pressure, piston gave way and slowly receded into the caliper. Was then able to install the new brake pad set, in conjunction with a new brake disc, with no further issue. Closed bleeder valve and exited assembly mode; caliper piston extended outward, fully taking up the existing slack between the brake pads and brake disc, when the brake pedal was depressed.
Successfully renewed brake pad set and rotor on fellow side, with no issue. Subsequently road tested vehicle; brake system was found to be fully operational.
I have the same model (2015 ML400) and I am about to replace my rear pads. Have you noticed the brake hardware clips are different sizes? I am installing Akebono European pads which are identical to the current pads, but the pad retaining clips (centric) are not the correct size (they don't fit). Any suggestions? thanks
I replaced my pads and rotors successfully today. The clips turned out to be no issue, just new so they had to be pressed harder into place.
But I still have a parking brake issue -- red "P" lights up on the dash with the dreaded red warning. I can clear it by running the pad replacement cycle, but I can't use the parking brake without it locking up the passenger side wheel.
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