Hi all,

Have a 2015 ML350 with ~39K on it that has been relatively flawless. I recently did rear brakes, simple pad change. The rotors looked healthy and fronts were still in good shape.
Took the car on a ~2,500 mile road trip and by the time we got home the outside pad on the passenger side was almost completely gone. The inner pad on this side and both pads on the drivers side were still in great shape.

Assuming something was dragging somehow I pulled it apart and replaced the pads on that side. Now we are probably another 2,500 miles on the pads, and while not as bad as last time - the outer pad on the passenger side is probably down to 20%. The inner pad probably at 80%.
After the last swap I did my best to verify nothing was dragging - car in neutral is super easy to push so it does not seem like the caliper is sticking or the parking brake.

I have to swap the pads again this weekend, but am eager to figure out what is going on. The brakes seem to operate fine - panic style test stops feel great, no pulling to one side and ABS engages as expected under super hard braking. But, clearly there is something going on out of the ordinary.

Has anyone experienced anything similar? It almost seems like there is a bias issue, maybe disloged some gunk in the brake lines when pushing the pistons back in, but again, the car feels completely normal under hard braking.
I may end up bleeding the brakes as well on this round but also looking for any other suggestions.

Thanks!

 

Ok, I'll bite...! From what you are stating, you have a sticking piston or two in a caliper, or sliders aren't greased properly.... and a pad dragging. Replace the caliper. When doing that, change out your brake fluid as you may have moisture locked in.
Just reread and have a question for you... When you replaced your pads, did you 1st retract the calipers via the maintenance option on the instrument panel? If you didn't, your question has been answered

 

Koenig1 is on the right track with the real question:

 

Hey guys,

Thanks for responding. First - yes I absolutely retracted the calipers each time I swapped the pads. Also, after this post I swapped the right rear pads again, the pins seemed fine, greased and move easily within the housing.
Service A was up this week so the wife took it in for the normal bits and had them take a peek. Said that since we did not reset the computer that it was sending more pressure to the rear pads.
The charge for the reset is a cool $300.

Seems like BS, but I will roll with it for now and update if I still have really bad wear at the rear.