Brake Service

1.17. Brake Service

Common tools that are used to repair hydraulic brake systems are: brake bleeder wrenches, vacuum brake bleeders, pressure brake bleeders, and valve gauge sets.

Bleeding of brakes is the process which removes air form the hydraulic braking system.

The three most common brake bleeding methods are: manual, pressure, and vacuum (gravity is also used). Flushing the brake fluid involves bleeding out the air and replacing the old brake fluid with new.

Always select the proper grade of brake fluid for the vehicle you are working on. Brake pedal inspection includes brake pedal height, free play, and travel.

Check the master cylinder for leaks if the brake fluid is low in the reservoir, the brake warning light is on, or the brake pedal reserve height is too low. Damaged brake lines should be replaced not repaired; always use the correct tubing bender to avoid kinks.

Inspect brake hoses for: cracks, bulges, abrasion or wear, kinks, and internal breakdown. 

Maintenance or servicing of the brakes involves only periodic (every 5000 km) checking and topping up the level of brake fluid in the master cylinder in case of hydraulic brakes and the adjustment of brakes to compensate the wear of the brake lining. Brake fluid used should be only of correct specification. 

Lubrication of the various linkages should be done at intervals, say every 5000 km. All the rubber cups and seals should be changed after every 60,000 km.

1.17.1. Inspection of brake system:

Before examining directly the brakes, it is always useful to inspect the other components of the vehicle which affect the performance of braking system. For example, if the tyres on the two sides of an axle are in widely different condition, one completely worn out and the other brand new, the braking effect will not be balanced. Similarly loose U bolts would either increase or decrease the braking effect, because then the axle will try to roll in directions of the braking pull, due to looseness of the U -bolts. In the same manner worn out wheel bearings or loose torque tube connections would affect the braking performance. All such defects, therefore, must be rectified before proceeding to inspect the brakes proper.

For examining the brakes, jack up the vehicle, placing the screw jack below the axles only, because then the springs will remain under deflection as they are normally on the road. If this precaution is not taken and the vehicle is jacked up at some frame points, the springs will no longer remain in the normal road position and in that case any adjustments made are not likely to be correct when the vehicle is run on the road required. After jacking up open up the brake drum and look out for any broken springs, loose anchorages worn out cam etc. which has to be replaced or tightened as required. Inspect the brake lining for wear. If the lining is worn to within about 1 mm of the rivet heads, or is otherwise scored, it has to be replaced.

Fig 1.28: checking pad for wear

Fig 1.29: checking drum wear

Fig 1.30: measuring disc thickness