On rear disks there are no brake cylinders, only caliper pistons. You can usually peek in with a flashlight (I use a little LED flexlight to put the light right on the pad) to quickcheck pad thickness for disk brake inspections, front and rear. If I cannot absolutely see the pads, then I pull the wheels. 9 times out of 10 I can see the pads just fine. The brake cables pull shoes located inside the rotors on these bigger pickups, so a hanging cable won't ruin the disk pads, but will ruin the e brake shoes and/or the rotor inner drum surface. I inspect lots and lots of vehicles, and the front brakes wear quicker almost always unless there is a problem. You do want the rears to do some work, and that means they will and should wear. Generally, 40k miles or so out of front brakes and 60 to 80k from rears would be acceptable. More is gravy, but don't count on it. Towing, hauling etc. would be harder on brakes, and long highway cruising would increase your brake life. Caliper pins can get stuck, pads can stick in the anchors etc, causing extra brake wear. Manufacturers are not building in a lot of extra meat on the rotors, so a lot of them are shot (below spec) at brake time. 415 doesn't sound too bad, for brakes all around and 2 rear rotors if you got name brand stuff. I've seen Akebono ceramic pads cost over 100 bucks per set, and rotors 50 bucks apiece and up, for US/Canadian made.
works fine now. 