Although the front disc brakes on the Subaru Legacy provide 75 percent braking for the vehicle, it's not uncommon for the rear pads to wear quickly. One of the main reasons is because they're smaller than the front pads and feature less friction material. Depending on your geographical region, it's also not uncommon for the pads to become stuck in the caliper bracket and constantly drag on the rotors, which will cause premature wear. Areas that experience severe winter weather and use sand and salt on the roads are highly susceptible to this side effect.
Crack the rear lug nuts loose with a 19-mm wheel nut wrench.2
Lift the rear of the Legacy with a car jack, and support the rear axle onto jack stands. Place the jack stands on the rocker panels or rear frame rail. Do not place the jack stands beneath the rear drive shafts or you can bend them. Remove the wheel nuts and wheels.3
Disconnect the parking brake cable from the rear caliper lever (if applicable) with a pair of pliers.4
Remove the lower lock pin bolt with a 14-mm box end wrench and then pivot the caliper upward to obtain access to the pads without fully removing the caliper from the bracket. If necessary, use a screwdriver to help convince the caliper to pivot.5
Remove the inboard and outboard pad from the caliper bracket. If necessary, gently pry them out of the bracket, being careful not to score the rotor with the screwdriver. Remove the pad rattle clips from the caliper bracket and clean off the accumulated brake dust and corrosion with a wire brush. Snap them back into place and apply a light coating of anti-seize compound to the top where the pad tabs sit. Wipe any excess anti-seize compound from the rotor with a shop rag.6
Apply the shims to the pad replacement set and then spray the shims and backing plate of the pads with the anti-squeal brake spray. Allow a few minutes for the solution to become tacky. Install the inboard and outboard pad into the caliper bracket.7
Squeeze the rear caliper piston into the bore using a pair of 12-inch channel locks. Squeeze slowly and evenly. Replace the caliper over the pads and rotor, replace the lower lock pin bolt and tighten with the 14-mm wrench. Replace the parking brake cable to the caliper lever, if applicable.8
Repeat the process for the other side. Replace the wheel and wheel nuts, and tighten it flush to the hub flange. Lower the Legacy to the ground and then torque the wheel nuts to 65-foot lbs. with the torque wrench and a 19-mm socket. Pump the foot brake pedal a few times until it feels firm. Check the brake fluid in the master cylinder and, if necessary, add clean brake fluid to top off. Test drive the Legacy.