Document 823ZqBavJVognOxapqXM41YgK

LESSON ONE-MODULE 1 BRAKE SYSTEM DIAGNOSIS AND TESTING Pedal Goes Down Fast/Excessive Pedal Travel A WARNING: IF THE BRAKE PEDAL GOES DOWN FAST, IT MAY INDICATE AN EXTREME PRESSURE LOSS IN THE BRAKE HYDRAULIC SYSTEM OR BRAKE SHOES OR CALIPERS THAT ARE SEVERELY OUT OF ADJUSTMENT. CHECK FOR PROPER OPERATION OF THE VEHICLE BRAKES BEFORE OPERATING THE VEHICLE. A pedal that goes down too fast could be caused by: Leaks in the hydraulic system. Air in the hydraulic system. Internal leaks in the master cylinder. Severe disc brake "knock back." - This occurs when the caliper piston is pushed back into the caliper bore by a rotor with excessive lateral runout or worn bearings. Worn or severely misadjusted brake shoes or pads. Leaking ABS outlet valves. Pedal Goes Down Fast/Excessive Pedal Travel Diagnosis To find the cause of a pedal that goes down fast, perform the following tests: Check the fluid level in the master cylinder. Check for external leaks in the hydraulic system. Check for external leaks at the master cylinder. Check for a internal leaks in the master cylinder. Check the rear brake adjustment. Check for brake cylinder "knock back." - To perform this check, inspect for brake rotor runout as described under Brake Roughness Diagnosis in this book. Bleed the hydraulic system. Follow the Soft or Hard Brake Pedal Symptom Chart in the ABS Section of the Workshop Manual to diagnose a possible leaking outlet/dump valve in the ABS EHCU. 14 September, 2005 Brake System Diagnosis and Repair