Disc and Drum Brake Inspection and Maintenance
Disc Brake Verification
Operation is checked by observing whether the pedal displacement causes the correct movement of the caliper. If not, remove it and repair it. Verify that there are no fluid leaks in the actuator or the hose union. Check the condition of the disc and pads. The pads should be replaced if they are defective. The process of disassembling the pads depends on the brake thickness. The brake pads should be superior to 2mm. When some are defective, all of the pads on the same axle must be replaced. When making the change to new brake pads, the greater thickness requires moving the plungers of the cylinders. This operation is performed with the help of a jack. When irregular wear is observed on the pads of a single wheel, it must be checked that the piston in the cylinder is not jammed and that the caliper slides correctly. Irregular brake engagement and wear can be caused by a seized piston. In this case, dismantle the piston for cleaning. In any case, if anomalies such as scratches or abrasions are found, the assembly should be replaced. The extraction of the piston is facilitated by using hydraulic pressure actuation with care on the brake pedal or using compressed air that is introduced by the arrival of the liquid orifice, ensuring that the piston does not hit anything on its way out. To assemble, lubricate the surfaces of the cylinder and the piston with abundant brake fluid. After assembly, verify that there are no leaks by immersing the whole assembly in a pot with water and applying air through the liquid inlet of the cylinder to a pressure less than 2 bar, blocking the plunger with a piece of wood. The continuous rise of bubbles indicates leaks, in which case take it off again and replace the piston ring or seal. As for the brake disc, it must be replaced when wear is more than 10% of its thickness, which is checked by a micrometer. Also, check for twisting of the disc faces. To do this, position the disc on the probe of a dial indicator and rotate the disc by hand, observing the deviations of the needle. Warping should not exceed 0.1 mm, or it should be replaced. In this case, fit new pads.
Drum Brake Verification
After removing the brake drum and before continuing dismantling, inspect the condition of the components, their mounting position, and their degree of wear. Verify that the drum has no excessive wear or scratches on its friction surface. Otherwise, it should be rectified or replaced. Also, the ovality of the circular friction area must be less than 0.1 mm. In terms of the brake shoes, check that they are not distorted or have any early breaks. In this case, they must be replaced. Also, verify that the recoil springs are efficient. They should be replaced whenever the brake shoes are changed. The brake pad linings must not be dirty or full of oil. If they are, the brake pads or shoes should be replaced. Replacement becomes necessary when the lining thickness is less than 2 mm. The cylinders must be checked for fluid leaks prior to the revision and disassembly. After finishing the whole brake assembly, the shoes must be adjusted. In the conventional type, with the wheel lifted, act on the adjustment nut corresponding to each shoe, turning the key down to get the wheel to lock, then loosen it slightly so that it rotates freely without friction.