Bulletin BES 05-07 Subject: Brake Hydro-Boost Relief Valve Seal Fracture Vehicle Involved: General Motors, 2003-2004 model year Cadillac Escalade, Chevrolet Silverado, Avalanche, Suburban, GMC Sierra, Yukon, Savana, Hummer H2, and 2004 Chevrolet Tahoe Condition: During brake application an engine compartment noise similar to the noise of a steering wheel turned to a full stop position. May also have an increase in steering and braking effort. If this occurs, it could result in a vehicle crash without prior warning. These Vehicles may have a relief valve bore within the brake Hydro -boost module that is not to specification. An out-of-specification bore could result in a fracture of the relief valve o-ring seal within the module. Repair Procedure: Identify that the vehicle pertains to the recall GM TSB #04004A. With the ignition off pump the brake pedal 10 times to relieve stored hydraulic pressure. Remove and reposition the master cylinder away from the hydraulic brake booster so that the machined surface of the booster may be inspected. Inspect the two o-rings on the original valve for signs of damage; inspect the bore of the hydraulic brake booster for any pieces or debris using a non-metallic tool or a lint free towel. Insert the new relief valve into the bore and tighten to 13ft.lbs. Clean up any fluid that leaked out of the hydraulic brake booster while removing the original valve. Position the master cylinder and combination valves on the mounting bolts on the hydraulic brake booster. With the master mounted flush to the booster install the nuts to 24 ft. lb. ft. On vans install the diagonal brace and splash- guard. Install the two bolts and torque to 18ft.lbs. Start the engine and verify hydraulic brake booster function as good and assisted feeling. Turn the engine off and check the power steering fluid reservoir. Add fluid if necessary. Close the hood and test drive. NAPA Brake and Chassis ■ 4400 Prime Parkway ■ McHenry, IL 60050 ■ (815) 363-9000.