Replacing brake linings

Part 1. Preparation and safety

Objective

• Remove and replace drum brake linings.

Personal safety

Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection - such as rubber gloves and barrier cream
• Respiratory equipment - such as face masks and valved respirators

If you are not certain what is appropriate or required, ask your supervisor.

Safety check

• Never use any petroleum or mineral based products, such as gasoline, kerosene etc, to clean a braking system or its components. Doing so can result in a failure of the braking system and its components. This may result in serious injury, or damage to the vehicle.
• Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.

Points to note

• Linings are designed to withstand extreme heat generation during braking. The linings must be able to withstand these temperatures and still maintain their braking efficiency.
• Oil or grease contaminants on the lining can have an adverse effect on the co-efficient of friction of the linings.
• If you need to bleed your brakes, you may need to replace your brake fluid.
• If you are bleeding brakes on an older vehicle, or you don't know the vehicle's service history, it is good practice not to fully depress the brake pedal during bleeding.

Part 2: Step-by-step instruction

1. Prepare the vehicle
   Before you raise the vehicle you will need to remove some of the brake fluid from the master cylinder. Using a siphon, remove enough fluid to cause the reservoir level to be below the fill mark. This allows for a fluid expansion when you retract the wheel cylinder pistons for the new linings. Raise the vehicle using the correct procedure to a comfortable working height and remove the wheel assembly.
2. Remove and inspect the brake drum
   Remove the brake drum taking care to remove any locating screws and back off any manual adjusters if fitted during the removal process. Check for any signs of fluid leaks or grease leakage from a hub or axle shaft seal. Check the brake drum for any signs of cracks or other damage.
3. Inspect the brake lines
   Inspect the brake lines to see if there are any signs of leakage or deterioration of flexible and/or steel hoses. If replacement is required report this to your supervisor.
4. Remove the brake shoes and linings
   Install a brake cylinder clamp onto the wheel cylinder. This will prevent the piston coming out when you release the brake shoes. Check with the shop manual for the correct service tools you need to release the springs and clips. Using the correct tool, release the retaining clips and disconnect the return springs. Remove the worn brake shoes and their linings from the backing plate.
5. Check the retaining clips and return springs
   Check the condition of the return springs making sure they have not got spread coils that will reduce their efficiency. Check that the retaining clips are not damaged and will keep the brake shoes in position.
6. Install the new brake shoes
   Compare the new brake shoes and their linings to the original ones to make sure they are the correct replacements. Referring to the shop manual, install the brake shoes onto the backing plate. Install the return springs and retaining clips in accordance with the manufacturers specification and direction.
7. Refit the brake drum
   As the return spring tension takes effect, the wheel cylinder piston should move back into the cylinder. If it doesn’t you may have to manually retract the piston. Now refit the brake drum. Prepare the cylinder for bleeding using a clear bleeder hose and a jar with a small amount of brake fluid in the base. Open the bleeder screw and have your assistant slowly push the brake pedal down and observe the air bubbles coming out. Close the bleeder screw off, and have the assistant slowly release the pedal. Manually adjust the brakes if necessary to ensure that the drum rotates without binding. Refit the wheel and tire assembly using the correct procedure. Repeat this process for each of the other drum brake stations.
8. Bleed system if required and test
   If at the completion of the replacement process the brake pedal feels “spongy”, you should bleed the system of air from all of the brake stations. Using the correct procedure to do this, and at the completion of the job, you should recheck the system to ensure that a firm pedal is achieved, and that the wheels cannot be rotated when the brake pedal is applied. Have your supervisor check the system and verify the repair.