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Tech Article - Drum brake shoes - replacement and adjustment
Warning: The dust created by the brake system may contain asbestos, which is harmful to your health. Never use compressed air to blow it out with and don t inhale any of it. Wear an OSHA-approved filtering mask when working on the brakes. Don t, under any circumstances, use petroleum-based solvents to clean brake parts. Use brake cleaner or denatured alcohol only. Always replace drum brake shoes in pairs, front or rear) - never replace the shoes on only one wheel. Work on one brake assembly at a time so you don t mix up parts.
Caution: Whenever the brake shoes are replaced, the retractor and hold-down springs should also be replaced. They lose their tension over a period of time and may allow the shoes to drag on the drum and wear at a faster rate than normal, due to continuous heating/cooling cycle that the springs are subjected to. When replacing the brake shoes, use only high quality, nationally recognized brand-name parts.
Raise the front or rear of the vehicle and place it securely on jack-stands after loosing the wheel lug bolts. Block the wheel on the ground. Apply the parking brake to keep the vehicle from rolling, if you re removing the front wheels. Now take off the wheels.
Remove the clip which secures the speedometer cable to the left dust cap, on the left front wheel. Pry off the dust cap that protects the wheel bearing on all wheels.
Look over for cracks, score marks, deep scratches and hard spots, which will appear as small discolored areas, before reinstalling the drum. Remove hard spots with fine emery cloth. Have the drum turned by an automotive machine shop, if that doesn t do it or if any of the other conditions described above are evident. Note: Professionals recommend resurfacing the drums every time you do a brake job. Resurfacing eliminates the possibility of out-of-round drums. If the drums are worn so much that they can t be resurfaced without exceeding the maximum allowable diameter (stamped or cast into the drum), replace them. Remove the glazing from the surface with emery cloth or sandpaper, using a swirling motion, if you decide to skip resurfacing.
Now put the brake drum in. Install the bearing, the thrust washer and the axle nut and adjust the bearing, on front wheels.
Mount the wheel, hand tighten the lug bolts and lower the vehicle. Tighten the wheel lug bolts to the torque. Tighten the axle nut to the torque on rear wheels.
Raise the vehicle and support it securely on jackstands. If you re adjusting the rear brakes, release the parking brake.
Using firm pressure, depress the brake pedal several time, to center the brake shoes in the drum. Rotate the wheel until the hole in the brake drum is aligned with one of the star wheel adjusters, on 1969 and earlier models. Remove the rubber plugs from the brake backing plate on 1970 and later models.
Turn the star wheel of the adjuster, while rotating the wheel, using a brake adjusting tool or a screwdriver, until the brake shoe slightly drags on the drum. Note: It may be necessary to press on the brake pedal to center the shoes once or twice during the adjustment procedure, if the brakes are way out of adjustment. Now, turn the star wheel in the opposite direction three or four clicks so the wheel can turn freely.
Repeat the previous step on the star wheel of the other brake shoe, then perform the adjustment procedure to the rest of the wheels.
You want to check brake operation before driving the vehicle in traffic.
Wheel cylinder - removal, overhaul and installation
Note: If an overhaul is indicated (usually because of fluid leakage or sticky operation) explore all options before beginning the job. New wheel cylinder will make this job quite easy. If you decided to rebuild the wheel cylinder, make sure that a rebuild kit is available before continuing. Always rebuild or replace them in pairs (front or rear).
Loosen the lug wheel nuts. Raise the front, or rear, of the vehicle and support it on jackstands. Make sure to block the wheels still on the ground to keep the vehicle form rolling. Now remove the wheel(s).
Take off the brake drum and the brake shoes.
Get rid of all dirt and foreign material from around the wheel cylinder.
Unscrew the brake line fitting. Don t pull the brake line away from the wheel cylinder.
Remove the wheel cylinder mounting bolt(s).
Unhook the wheel cylinder from the brake backing plate and place it on a clean workbench. Unplug the brake line to prevent fluid loss and contamination, RIGHT AWAY! Note: If the brake shoe linings are contaminated with brake fluid, install new brake shoes.
Take off the bleeder valve, cups, pistons, boots and spring assembly from the wheel cylinder body.
Using brake fluid, clean the wheel cylinder, denatured alcohol or brake system cleaner. Warning: Do not, under any circumstances, use petroleum-based solvents to clean brake parts!
Using compressed air, remove excess fluid from the wheel cylinder and to blow out the passages.
Look over the cylinder bore for corrosion and score marks. You can use crocus cloth to remove light corrosion and stains, but the cylinder must be replaced with a new one if the defects can t be taken off easily, or if the bore is scored.
Lubricate the new cups with brake fluid.
Assemble the wheel cylinder components and make sure the cup lips face in.
Install the bolt(s) loosely, after placing the wheel cylinder in position.
Connect the brake line, but don t tighten it yet. Tighten the wheel cylinder bolt(s) securely, then tighten the brake line fitting. Now put in the brake shoes and the brake drum.
Now bleed the brakes.
Check brake operation before you drive the vehicle into traffic.