Cannot Retract Brake Caliper Piston

[EViS]

It's time to replace all the discs and pads on my 2013 Mercedes A250 (W176). I've started at off-side rear and all was going well until it came to retract the brake caliper piston back in to fit the new pads. It just won't squeeze in, I've even tried loosening the bleed valve and unscrewing the brake reservoir cap. I tried so hard that my brake piston wind-back tool snapped *sigh*.

In addition, is the black plastic box at the back of the caliper the electric parking brake actuator? Haven't come across this before, probably because I tend to work on slightly older/less sophisticated cars.

Edited by EViS on Sunday 18th August 15:45

[z_chromozone]

If it is anything like other electronic brake you will need to overuse using a laptop

[GreenV8S]

Cars with electronic parking brakes typically need to be put in service mode. A mechanic would use the computer for that but there is often a way to do it without a computer.

[Sheepshanks]

As well as other answers, don't know about that car but rears often wind in.

[E-bmw]

Sheepshanks said:

As well as other answers, don't know about that car but rears often wind in.

I think he said he was using a wind back tool as he said it snapped he tried that hard.

[Athlon]

The park brake needs to be in service mode before you try anything.
Some are left handed thread to wind back..

[Sheepshanks]

E-bmw said:

Sheepshanks said:

As well as other answers, don't know about that car but rears often wind in.

I think he said he was using a wind back tool as he said it snapped he tried that hard.

Sorry, you're right. I was thinking differently to what was written.

[M4cruiser]

Athlon said:

The park brake needs to be in service mode before you try anything.
Some are left handed thread to wind back..

Sometimes the piston does seize in the caliper. The brakes would continue to appear to "work" if the sliding mechanism can make the opposite pad do the work. Are the pads worn evenly?
Although I'm not familiar with that particular model, I have done pads and discs on other (more mundane) cars and had to free off both the piston and the caliper sliding mechanism a few times.

[Athlon]

M4cruiser said:

Sometimes the piston does seize in the caliper. The brakes would continue to appear to "work" if the sliding mechanism can make the opposite pad do the work. Are the pads worn evenly?
Although I'm not familiar with that particular model, I have done pads and discs on other (more mundane) cars and had to free off both the piston and the caliper sliding mechanism a few times.

I know, I fix them for a living! Rare for a Mercedes caliper to seize to be honest.

Bottom line is the guy is risking damaging things if he does not have the gear, you must have it in service mode before retracting the piston.

[softtop]

Have you disconnected the brake system from the car under the bonnet? Google what you need to do, this then puts it into 'service mode' This was the case with my old 2003 E Class.

[EViS]

Thanks all . I feel like such a numpty! First car I've ever worked on with an electric brake and obviously didn't appreciate fully how they function! A quick search and I found how to get into the service menu to wind the electric brake back, smooth sailing from there!

Here's hoping I didn't damage anything with the excessive force I put into the wind-back tool . Took the car for a quick drive and engaged the parking brake a couple of times, all seems well atm.