tcpy

2004 e320 rear wheel drive.

Replacing front brake pads and rotors.

Done quite a few brake and rotor replacements before and even on a 2006 mercedes c class but never had this type of issue.

Basically I didn't know about the sbc brake system and attempted to replace the pad and rotors on the front tires. Sucessfully replaced the passenger side. Then when I got to the other side, found the caliper piston fully compressed. Used a c clamp to decompress it but it didn't work, only got it half way. Researched and found out I activated the sbc system some how. What do I do now, how to I depressurize the pistons so I can decompress and finish replacing the pads and rotors?

Thanks

tjts1

Unplug SBC.

F1Fan

Put the clamp back on the brake caliper. Then slowly and gently release the bleeder valve to let out brake fluid out of the caliper. Keep a towel handy as it will spill out. I would gently release and close the valve until you've compressed the brake piston back far enough. Also, don't open any doors or push any buttons on your keyfob while working on your brakes. That will start the sbc wake up procedure.

bbirdwell

Either deactivate the SBC with STAR or unplug the unit. If the unit is not deactivated or unplugged, opening a door, pushing the parking brake, unlocking the car...any of these will activate the system and place around 900 psi on the pistons. This has been discussed multiple times on this forum. Search and read before you injure yourself or damage your car. The brake system is brake-by-wire, not the historical system hydraulically operated by the brake pedal.

kajtek1

SBC plugs were subject to recall, so I hesitated to touch them.
The method of pushing tow button, locking the car and putting the knob in safe location always work for me.
I also like to bleed the fluid during pads changes, instead of pushing contaminated fluid from calipers back into pump.