Braking System Troubles

Road safety largely depends both on the condition of the vehicle brakes and on the driver's skill in applying them. When you are operating a tractor or automobile, do not apply the brakes too frequently or too hard, for this accelerates wear of the brake linings and brake drums.

The various braking system troubles result in poor braking action, vehicle pulling to one side during braking, and failure of the brakes to release.

Poor braking action may be caused by loss of brake fluid or compressed air due to leaky brake lines or flexible hoses, air in the hydraulic brake system, brake shoes out of adjustment, grease or brake fluid on the shoes, or excessively worn brake shoes or drums.

The points of leakage in the hydraulic brake system usually are easy to find because they will be covered with dirt that has stuck to the fluid as it leaked out. A leaky condition of the air brake system will cause the air pressure to drop when the engine is stopped. (Note that air pressure dropping while the engine is running points to a faulty brake compressor). Leaky spots in the air brake system can be detected by listening for the hissing of escaping air, or by applying soapy water to brake line connections where air leaks are most likely to occur. If there is a leak, air bubbles will show.

Air trapped in the hydraulic brake system will cause the brake pedal to go to the floorboard, or it will make the pedal soft or spongy. To remove air from the system, the latter must be "bled". This procedure requires two persons to perform. The sequence of operations is as follows. Add brake fluid to make its level in the fluid reservoir of the brake master cylinder stand 15 to 20 mm below the filler hole. Remove the rubber cap from the bleeder valve on the right rear wheel cylinder and fit a rubber hose 350 to 400 mm long on the valve head. Immerse the other end of the hose in a half-liter glass jar filled half its capacity with brake fluid. Unscrew the bleeder valve one half to three fourths of a turn. Tell your assistant to pump the brake pedal several times. The pedal should be depressed quickly and released slowly. Continue pumping the pedal until air bubbles stop escaping from the hose in the jar. Add brake fluid to the reservoir every five or six pumpings of the pedal to keep the reservoir filled and prevent air entering the system through the master cylinder. As soon as air bubbles cease escaping from the hose, tighten the bleeder valve securely with the brake pedal fully depressed.

Repeat the procedure for all the other wheels in the following sequence: front right, front left, and then rear left.

With the system free from air and the brake arrangements adjusted properly, the brake pedal must go no more than half the distance to the floorboard.

Oil can get onto the brake shoes from faulty axle shaft seals. Should this prove to be the case, the seals must be replaced and the shoes and drums washed with gasoline. After washing, the brake linings must be rasped or wire-brushed.

Worn brake linings should be replaced and then the clearance between the new linings and the drum adjusted.

If the air brake system loses air, the cause must be revealed and the trouble corrected.

A vehicle pulling to one side during braking may cause skidding accidents. This trouble means that more braking friction is being applied to one brake drum than the other. The problem could be caused by grease or brake fluid on brake linings, brake shoes out of adjustment, sticking brake camshafts or wheel brake cylinder pistons, or restricted brake lines or hoses.

Brake linings with grease or brake fluid on them must be washed with gasoline and then rasped or wire-brushed. Improper brake shoe adjustment should be corrected. Stuck brake camshafts should be removed, cleaned, lubricated, and installed in place. Wheel brake cylinders with stuck pistons must be replaced. Restricted brake lines or hoses must be cleared with compressed air.

Failure of the brakes to release may be due to sticking components in the wheel brake arrangements. This may be caused by brake linings broken loose from their shoes, brake shoes frozen to the drums, broken brake springs, clogged air vent and compensating holes in the brake master cylinder, or stuck pistons in the wheel brake cylinders.

Brake shoes frozen to the drums can be freed by heating the drums to melt the ice. Broken components should be replaced. Clogged holes in the master cylinder should be cleared with a piece of copper wire. Wheel cylinders with stuck pistons must be replaced.

Failure of parking brakes to hold usually is caused by excessive clearance between the brake shoes or band and the drum or pulley. This trouble is corrected by properly adjusting the clearance.