How to Repair a Rear Drum Brake on a 1978 Ford Mustang King Cobra

The 1978 Ford Mustang "King Cobra" uses a duo-servo style rear drum brake system. In this type of system , as the brake shoes are expanded against the drum by the wheel cylinder, the shoes try to follow the rotation of the drum. As the front shoe rotates, it forces the rear shoe hard into the drum to provide stopping power. This is the reason the rear shoe is always larger than the front shoe. Repairing the rear drum brakes on this car is similar to other Ford vehicles equipped with a similar brake system.

Instructions

Force wheel chocks in front of and behind the front wheels. Loosen the rear wheel lug nuts 1/2 turn using the lug wrench. Position a floor jack under the center of the rear differential (also called a rear end), and lift the car until the rear wheels are off the ground.

Slide jack stands under the rear axle tubes on the rear end, and lower the Mustang onto the stands. Remove the rear wheels using the lug wrench. Lay the wheels and lug nuts aside to prevent loosing the lug nuts and tripping over the wheels.

Slide the drums off the brake shoes. It is not uncommon for the drum to be stuck to the axle hub. If this occurs, a few sharp blows, with a hammer, around the outer edge of the drum will loosen the drums enough to be removed. Wash the brake shoes and drums off with soapy water to remove accumulated brake dust.

Pull out slightly on the self-adjuster lever located between the bottom ends of the shoes, and rotate the serrated adjuster wheel behind it until it is as loose as possible. Remove the two return springs that connect the shoes to the pivot pin, located at the top of the brake assembly backing plate, using the return-spring tool in the brake spring tool set. Set the return springs, adjuster cable, cable guide and parking brake bar (located between the two shoes just below the wheel cylinder) aside.

Pull the lower edges of both brake shoes away from each other until the adjuster drops out from between them. Push the shoes together and slip the lower spring off the adjuster lever. No special tool should be needed to do this. Lay the adjuster lever and lower spring aside.

Push in on the two hold-down springs that attach the shoes to the backing plate, using the hold-down spring tool, and rotate the spring 1/4 turn to release the springs from the hold down pin. Lat the front shoe aside. Spread the u-clip that attaches the parking brake lever to the rear shoe, using a screwdriver, and remove the shoe from the lever. Lay the shoe aside.

Clean the backing plate thoroughly with soapy water and a scrub brush. Dry it using shop towels. Apply a dab of silicon brake grease to the pivot pads on the backing plate. These are the raised areas on the backing plate that the shoes contact when they are installed.

Install the new rear shoe (the larger of the two shoes) onto the parking brake lever, and attach it to the backing plate using the hold down springs. Attach the new front shoe to the backing plate in the same manner. Position the parking brake bar between the shoes and slide the adjuster cable onto the pivot pin. Install the two return springs and the adjuster cable guide using the return spring tool to pry the springs onto the pivot pin.

Slip the adjuster lever into the hole on the brake shoe, and hook the adjuster cable to it. Attach the lower spring to the rear shoe, and slip it into the adjuster lever while pushing the shoes toward each other. Pull the shoes away from each other, and slip the adjuster between them.

Slide the small side of the shoe-adjusting gauge into the new brake drum, and spread it out against the inside of the drum. Tighten the thumbscrew on the gauge to lock it in place. Slide the larger side of the gauge over the shoes. Rotate the adjuster on the brake system until the gauge makes slight contact as it is passed over the shoes. Slide the new drum into place over the shoes. Repeat the steps for the remaining rear brake assembly. Reinstall the rear wheels.

Raise the Mustang off the jack stands, and remove the stands. Lower the car to the ground, and tighten the lug nuts one final time. Test drive the car to verify it stops properly and the parking brake functions properly.