2. Visually inspect for obvious signs of mechanical damage.
Mechanical factors
- Tire pressure
- Wheels and tires
- Leakage in the lines of the brake system
3. If an obvious cause of the observed problem is found, correct it before proceeding to the next steps (if possible).
4. If the cause is not visually obvious, check the symptom and refer to the Symptom Chart.
Road test
Carry out a road test to compare the actual performance of the vehicle's brake system to the performance standards the driver expects. The test driver's ability to make correct comparisons and identify a fault depends on experience. In order to correctly compare and identify malfunctions in operation, the driver must thoroughly know the features of the brake system and generally accepted quality standards.
An experienced brake mechanic always sets up road test routes with complete brake system diagnostics. For this, roads with a sufficiently smooth and even road surface are selected. Gravel or bumpy roads are not suitable because their surface does not provide even tire grip on the road. Roads with a convex cross profile should be avoided, since on such roads a significant proportion of the mass is transferred to the wheels located below. If a route is selected and used continuously, the test results may not include a pavement correction factor.
Obtain a full description of the customer's complaint or suspected condition before conducting a road test. Based on the description and his own experience, the mechanic can compare the possible causes and symptoms of the problem. Certain elements are flagged as possible sources of failure, other elements are discarded based on available information. More importantly, descriptions received from the customer may indicate the presence of dangerous conditions that should be checked or corrected before road testing. The description also helps to define the overall road test approach by narrowing down the troubleshooting to specific elements, speed or driving conditions.
Start your road test with a general brake performance test. Bearing in mind the nature of the complaint received, check the operation of the brakes at different speeds, applying weak and strong pressure to the brake pedal. To determine if the complaint is related to the front or rear brake system, apply the brake pedal and then apply the parking brake lever. If the marked state (vibration, ripple, pulsation) occurs only when the parking brake is applied, the fault relates to the rear brake system.
Avoid blocking brakes and slipping tires. Locked brakes and sliding tires are not indicators of braking performance. A wheel that is subjected to strong braking and steering force will stop the vehicle in a shorter stopping distance than locked brakes.
If a fault is found during this check, verify that it matches the description obtained prior to the road test. If the cause of the complaint is not obvious, try to reproduce the condition using a description.
If a fault exists, use the Symptom Table to map the fault to a specific subsystem and a description of the condition. A list of possible causes based on this description can be used to further refine the cause of the failure and map it to a specific item or condition.
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