The parking/emergency brake must hold the vehicle on any grade. This requirement covers both passenger and commercial motor vehicles equipped with either the enclosed type brake at each rear wheel or a single brake mounted on the drive line. The Federal Motor Carrier Safety Regulations Pocketbook, par. 393-52. lists emergency brake requirements.

BRAKE SYSTEM INSPECTION

Most vehicle manufacturers recommend periodic inspection of the brake system. This involves checking the fluid level in the master cylinder, brake pedal action, condition of the lines and hoses, and the brake assemblies. These checks are to be performed during the preventive maintenance (PM) cycle.

Checking Master Cylinder Fluid Level

An important part of the brake system inspection is checking the level of the brake fluid. To check the fluid, remove the master cylinder cover, either by unbolting the cover or prying off the spring clip. The brake fluid level should be 1/4 inch from the top of the reservoir.

CAUTION

Use only the manufacturer's recommended type of brake fluid. Keep grease, oil, or other contaminates out of the brake fluid. Contamination of the brake fluid can cause deterioration of the master cylinder cups, resulting in a sudden loss of braking ability.

Brake Pedal Action

A quick and accurate way to check many of the components of the brake system is by performing a brake pedal check. Applying the brake pedal and comparing its movement to the manufacturer's specifications does this. The three brake pedal application distances are as follows:

BRAKE PEDAL FREE PLAY, which is the amount of pedal movement before the beginning of brake application. It is the difference between the "at rest" and initially applied position. Free play is required to prevent brake drag and overheating. If pedal free play is NOT correct, check the adjustment of the master cylinder pushrod. If this adjustment is correct, check for a worn pedal bushing or a bad return spring, which can also increase pedal free play.

BRAKE PEDAL HEIGHT, which is the distance from the pedal to the floor with the pedal at rest. If the height is incorrect, there may be worn pedal bushings, weak return springs, or a maladjusted master cylinder pushrod.

BRAKE PEDAL RESERVE DISTANCE, which is measured from the floor to the brake pedal with the brake applied. The average brake pedal reserve distance is 2 inches for manual brakes and 1 inch for power brakes. If the reserve distance is incorrect, check the master cylinder pushrod adjustment. Also, there may be air in the system or the automatic brake adjusters may not be working.

Brake System Leaks

If the fluid level in the master cylinder is low, you should check the system for leaks. Check all brake lines, hoses, and wheel cylinders. Brake fluid leakage will show up as a darkened, damp area around one of the components.

Checking Brake Assemblies

When inspecting the brake system, remove one of the front and rear wheels. This will let you inspect the condition of the brake linings and other components.

INSPECTING DISC BRAKES. - Areas to check when inspecting disc brakes are the pads, the disc, and the caliper. You should check the thickness of the brake pad linings. Pads should be replaced when the thinnest (most worn) part of the lining is approximately 1/8 inch thick.

Check the caliper for fluid leakage at the piston seal and missing or damaged clips/springs. The disc should be checked for damage, such as heat cracks, heat checks (overheating causes small hardened and cracked areas), and scoring. Wheel bearings should be checked and adjusted if necessary. To check for rattles, strike the caliper with a soft-faced rubber mallet. To repair any of these problems, consult the manufacturer's service manual.

INSPECTING DRUM BRAKES. - Areas to check when inspecting drum brakes are the brake shoes, the brake drums, the wheel cylinders, and other related parts. Once the wheel is removed, you must remove the brake drum that will expose all parts requiring inspection.

The brake shoe linings must NOT be worn thinner than 1/16 inch. They also should NOT be glazed or coated with grease, brake fluid, or differential fluid. Any of these conditions require lining replacement.