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LESSON ONE-MODULE 1 BRAKE SYSTEM DIAGNOSIS AND TESTING Excessive Brake Pedal Effort Excessive brake pedal effort is characterized by a very stiff brake pedal and increased stopping distances. Excessive brake pedal effort can be caused by: Vacuum assisted brakes. - Improper brake booster operation. - Improper booster operation could also be caused by a lack of vacuum due to leaking or restricted vacuum lines, a faulty booster check valve, low engine vacuum, or a faulty vacuum pump (diesel engines). Hydraulic assisted brakes. - Improper brake booster operation. - Improper booster operation could also be caused by low power steering fluid level, a loose or damaged accessory belt, or a faulty power steering pump. Binding brake pedal bushing. Faulty brake pressure control valve. Overheated brakes. Excessive Brake Pedal Effort Diagnosis To determine the cause of excessive brake pedal effort, perform the following tests: Inspect for binding and wear at the brake pedal bushing. Check brake booster operation. Check brake pressure control valve for contamination. 18 September, 2005 Brake System Diagnosis and Repair