13 Steps in Brake System Inspection and Training Part I
Brake system service begins with thorough testing and inspection. The following 15-step checklist will help you evaluate all brake systems with greater accuracy and efficiency.
1. Service Brake Performance: A service brake performance test or test of overall stopping ability, is a good way to begin a brake inspection and is essential for evaluating completed brake services. Brake performance can be tested on a brake dynamometer or platform analyzer or by a simple road test.
On a dynamometer, the braking forces at the front and rear axles are tested separately. On a platform analyzer, the braking forces at all four wheels are tested simultaneously. Generally, the total braking force of the vehicle weight, and the braking force at the wheel must be within 20 percent of the force on the opposite wheel of the same axle.
When brake performance is evaluated by a road test, the vehicle should stop smoothly within 25 feet from 20 mph without swerving out of a 12-foot-wide lane.
2. Brake Warning Light: on 1967 and later vehicles with split hydraulic systems, check the warning light by momentarily turning the ignition switch to the Start position. But, do not start the engine. See if the warning light illuminates because it should. Some imported cars have press-to-test warning lights, which are checked by pressing on the indicator lamp. Again, the lamp should light.
3. Stop lamps: Check the stop lamps by depressing the brake pedal and watching for both lamps to light.
4. Pedal and Linkage Installation: Apply and release the pedal several times. Move the linkage from side to side. Check for noise, binding and excessive looseness. Troubles will soon follow these signs so better fix them right away.
5. Pedal Reserve: Pedal reserve is the distance from the pedal to the floor when the brakes are applied. To check pedal reserve, release the parking brakes and for cars with power brakes, start the engine. Measure the distance from the pedal free height to the floor. Depress the pedal and measure the distance from the brake-applied position to the floor.
Pedal travel from the released to the applied position should be 80 percent or less of its total height from the floor. Pedal reserve must be 20 percent or more. Another general guideline is that the pedals should be at least two inches from the floor for manual brakes and one inch for power brakes.
While checking pedal reserve, pump the pedal several times at a rapid pace. If the brake-applied pedal height rises with repeated exertions, or if the pedal feels rather spongy, there may be air in the hydraulic lines or the drum brakes of the car may need adjustment.
6. Hydraulic Leakage: check for hydraulic leakage by applying the brake pedal firmly and holding it for 10 seconds. If the peal drops under pressure after the initial application, or if the warning light turns on, the hydraulic system is leaking.
7. Vacuum Reserve: on a car with vacuum-operated power brakes, run the engine at a fast idle for several seconds an then turn it off. Wait 90 seconds and apply the brakes several times. Two or more applications should be power assisted. The pedal should get firmer with four or five applications.