2. Visually inspect for obvious signs of mechanical damage.
Mechanical factors
- Tire pressure
- Wheels and tires
- Leak in brake system lines
3. If an obvious cause for the observed problem is found, correct it (if possible) before proceeding with further actions.
4. If the cause is not visually obvious, check the malfunction symptom and refer to the Malfunction Symptom Table.
Road test
Conduct a road test to compare the actual performance of the vehicle's brake system with the performance standards expected by the driver. The test driver's ability to make correct comparisons and identify the fault depends on experience. To make correct comparisons and identify malfunctions, the driver must thoroughly know the features of the brake system and generally accepted quality standards.
An experienced brake mechanic will always design road test routes with a full brake system diagnostic. Roads with a sufficiently smooth and level road surface are selected for this purpose. Gravel or pothole roads are not suitable, since their surface does not provide uniform grip of the tires to the road. Convex roads should be avoided, since on such roads a significant proportion of the weight is transferred to the wheels located below. If a route is selected and used constantly, the road surface correction factor can be ignored in the test results.
Before conducting a road test, obtain a complete description of the customer's complaint or suspected condition. Based on the description and the mechanic's own experience, the mechanic can match possible causes and symptoms of the problem. Certain items are flagged as possible sources of the problem, and other items are eliminated based on the information available. More importantly, the customer's description may indicate dangerous conditions that should be checked or corrected before conducting a road test. The description also helps determine the overall approach to conducting the road test by narrowing the search for causes of the problem to specific items, speeds, or driving conditions.
Begin the road test with a general brake performance check. Keeping in mind the nature of the complaint received, check the brake action at various speeds by applying light and heavy pressure to the brake pedal. To determine whether the complaint is related to the front or rear brake system, apply the brake pedal and then apply the parking brake lever. If the noted condition (pull, vibration, pulsation) occurs only when the parking brake is applied, the fault is related to the rear brake system.
Avoid locking brakes and sliding tires. Locked brakes and sliding tires are not indicators of braking efficiency. A wheel that is subject to strong braking and turning force will stop the car in a shorter stopping distance than a wheel with locked brakes.
If a fault is found during this check, check whether it matches the description given before the road test. If the cause of the complaint is not obvious, try to reproduce the condition using the description.
If a fault exists, use the Fault Symptom Table to match the fault to a specific subsystem and condition description. The list of possible causes generated from this description can be used to further narrow down the cause of the fault and match it to a specific component or condition.
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