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repeat steps 2-4. 9. If none of these conditions were found with the engine vacuum hose, then there is an engine vacuum source problem, check the engine vacuum system. 10. Remove the vacuum brake booster check valve from the booster. 11. Install the check valve to the engine vacuum hose. 12. Install the vacuum gage to the check valve. 13. Start the engine and allow the engine to idle in PARK with the A/C system OFF, until normal operating temperatures are reached. 14. Turn the ignition OFF. 15. Check to see if the engine vacuum reading is maintained within the specified normal engine vacuum range. Specification: 47-68 kPa (14-20 in Hg) 16. If the engine vacuum reading is maintained within the specified normal range, proceed to step 18. 17. If the engine vacuum reading is NOT maintained within the specified normal range, replace the brake booster check valve, then repeat steps 11-15. 18. Inspect the brake booster check valve grommet for the following conditions: Loose connection to the vacuum brake booster Deformation or contamination Cracks, cuts, dry-rot 19. If any of these conditions were found with the check valve grommet, replace the grommet. HYDRAULIC BRAKE ASSIST SYSTEM NOISE INSPECTION Tools Required J 28662 Brake Pedal Effort Gage. See Special Tools. Inspection 1. Install the J 28662 to the brake pedal. See Special Tools. 2. Start the engine and allow it to idle. Ensure that the wheels are directed straight ahead. 3. Apply and maintain the brakes with 111 N (25 lb) of force to the brake pedal, as indicated on the J 28662 . See Special Tools. Observe for noises. 4. Quickly release the brakes. Observe for noises.
2008 Chevrolet Silverado 1500 2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
5. If chatter and/or a vibration of the brake pedal was apparent during the brake system apply of 111 N (25 lb) of force, the power steering pump drive belt not may have proper tension 6. If any significant noise was apparent during the quick release of the brakes following the brake system apply of 111 N (25 lb) of force, there is likely a restriction in the hydraulic 7. Apply the brakes with 178 N (40 lb) of force to the brake pedal, as indicated on the J 28662 , then gradually increase pedal effort up to 445 N (100 lb) of force for not more than 8. Quickly release the brakes. Observe for noises. 9. If a hiss noise was apparent and increased during the brake system increasing apply of 178- 445 N (40-100 lb) of force, the hydraulic brake booster assist system is operating normally 10. If a clunk, chatter, and/or clicking noise was apparent during the quick release of the brakes following the brake system increasing apply of 178-445 N (40-100 lb) of force, the BRAKE SYSTEM EXTERNAL LEAK INSPECTION 1. In order to inspect for external brake fluid leaks, first check the fluid level in the master cylinder. While a slight brake fluid level drop can be considered a normal condition due to brake 2. If the fluid level is abnormally low, adjust the brake fluid level. Refer to Master Cylinder Reservoir Filling. 3. Start the engine and allow it to idle. IMPORTANT: Do NOT apply 445 N (100 lb) of force or more to the brake system pedal for more than 5 seconds at a time. CAUTION: Refer to Brake Fluid Irritant Caution . NOTE: Refer to Brake Fluid Effects on Paint and Electrical Components
2008 Chevrolet Silverado 1500 2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
4. Apply constant, moderate foot pressure to the brake pedal. If the brake pedal gradually falls away while under foot pressure, there may be a brake fluid 5. Turn OFF the ignition. 6. Visually inspect the following brake system components for brake fluid leaks, excessive corrosion, and damage. Give particular attention to all brake pipe and flexible hose Master cylinder brake pipe fittings All brake pipe connections Brake pipes Brake hoses and connections Brake calipers and/or wheel cylinders, if equipped 7. While slight dampness around the master cylinder reservoir can be considered acceptable, brake fluid leaking from any of the brake system components requires immediate attention. BRAKE SYSTEM INTERNAL LEAK TEST 1. Start the engine and allow it to idle. 2. Apply light, steady pressure to the brake pedal. Observe both the brake pedal feel and travel. 3. Release the brakes and turn OFF the ignition. 4. If the brake pedal apply felt spongy, but the brake pedal travel was not excessive, perform the following steps: 1. Inspect the brake system for external leaks. Refer to Brake System External Leak Inspection . CAUTION: Refer to Brake Fluid Irritant Caution . NOTE: Refer to Brake Fluid Effects on Paint and Electrical Components
2008 Chevrolet Silverado 1500 2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
2. Pressure bleed the brake system in order to purge any air that may be trapped in the system. Refer to Hydraulic Brake System Bleeding (Pressure)Hydraulic Brake Fig. 3: Cross Sectional View Of Brake Master Cylinder 5. If the brake pedal apply did not feel spongy, but the brake pedal travel was excessive, perform the following steps: 1. Loosen the master cylinder-to-brake power booster mounting nuts. 2. Carefully pull the master cylinder away from the brake power booster just enough to inspect the mounting surface of the master cylinder. 3. Inspect the master cylinder mounting surface at the primary piston (2) for brake fluid
2008 Chevrolet Silverado 1500 2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
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