The only thing substantially different between the front and rear brakes on the ML320 will be evident when (if) you remove the rotor. The rear rotor actually has an inner drum with brake shoes used for the parking brake. Sometimes that systemâ€™s adjustment wheel has to be turned to relieve pressure between the shoes and drum before the rotor can be pulled free from the hub â€“ exactly like working on an old drum brake system. Of course that canâ€™t happen until you remove the disc brake pads and caliper, which is the problem, right?
The rear caliper is mounted very similarly, if not exactly the same, as the fronts with a bolt. Or is it two bolts? Pardon my memory lapse, but Iâ€™ve worked on so many disc brake systems, I forget, but if you got the fronts off, the rears should be no problem. Here are some pointers.
After removing the road wheel, and before removing the caliper bolt(s), use something such as a large flat-blade screwdriver positioned strategically to pry the pads away from the rotor. Be careful not to damage anything (rotor, caliper or hoses). Of course if you are replacing the rotors, then they make an excellent place to pry. Otherwise, you should be able to find a good place between the pad and the caliper or the caliper and the hub or slides. You will be pushing the brake cylinder back into the caliper against the hydraulic fluid, so use a firm, steady pressure. I would recommend pushing the cylinder all the way in as far as you can go since you are going to need plenty of clearance for the new, thicker pads. If you donâ€™t do it now, you will need a C-clamp to do it once you remove the caliper.
Once you have pushed the cylinder into the caliper, remove the bolt(s) holding the caliper to the hub. The pads are clipped to the caliper, so both pads and the caliper will come off the rotor in one assembly. The pads have notches that ride along the slides, and either the top or bottom will have to come out first. You may have to lift up on the caliper and pull the bottom out, letting the top pad notches pivot on the top slide (or vice-versa). Once you do this, you should be in good to replace the pads. If this does not do the trick, let me know and Iâ€™ll see what I can help you with.