To change the rear disc Brake Backing Plate on the 25/3500 series, you must disable the park brake cable automatic adjuster and take off the park brake shoe. Then, loosen and take away the backing plate nuts, and remove the backing plate from the axle housing flange. Attach the backing plate to the axle housing flange, and screw in the backing plate nuts until you reach 135 nm (100 ft. Lbs.) of tightness. Then, put the park brake shoe back in place, check and adjust it, and resume the park brake cable automatic adjuster. Remember to follow brake dust caution and fastener notice during the whole process.