Service Procedure
InspectionTools Required
CH 47950 Hydro-Boost Checking Tool
1. With the vehicle transmission in PARK or NEUTRAL, set the park brake.
2. With the engine OFF, make a minimum of five (5) high effort brake applies until the pedal feels hard.
3. Start the engine.
Important:
DO NOT depress the brake pedal until instructed.
4. Turn the steering wheel to the "steering lock" (fully turned) position. Hold at the steering lock position for 1 to 2 seconds and then release the steering wheel. Repeat a total of 3 times.
5. Turn the vehicle off being careful not to step on the brake pedal.
6. For Express/Savana only:
A. Remove the remote power steering reservoir mounting nuts.
B. Disconnect the reservoir outlet hose from the booster unit. Keeping the hose end higher than the reservoir, reposition the reservoir forward and down out of the way.
7. Using a clean, lint-free shop cloth, wipe any dirt away from the steering pump supply hose/tube connection area on the hydro-boost (this is the center hose/tube of the three).
8. Disconnect the power steering supply hose/tube from the hydro-boost unit and wrap a clean lint-free shop cloth around the end of the hose and secure it in the engine compartment.
9. Using a clean lint-free shop cloth, clean any dirt off of the inlet port adapter valve assembly. Before installing the inlet port adapter, place a shop cloth below the booster supply port in order to capture any fluid exiting the hydro-boost unit.
10. Install the inlet port adapter, CH 47950-2 (2) into the booster supply port.
11. Using a torque wrench, slowly tighten the inlet port adapter to 16 N.m (12 lb-ft). If the clear tube was removed from the inlet port adapter assembly, be sure it is reinstalled.
12. Before each use of the accumulator pressure clamp, CH 47950-1, be sure to grease the clamp bolt and anti rotation washer with wheel bearing grease.
13. Install the accumulator pressure clamp, CH 47950-1 (1), by sliding it over the accumulator and straddling the hydro-boost housing.
14. Confirm that the accumulator pressure clamp is squarely seated onto the booster housing and accumulator, and place the 3/4 inch containment bolt into the fixture. Install the nut hand-tight onto the containment bolt.
15. Check and make sure that the fixture washer is correctly positioned between the end of the accumulator, and that the pin is engaged in the end of the bolt. The tab on the washer should be rotated clockwise so it is located below the master cylinder mounting flange ear.
Caution:
Incorrect installation of the washer will result in damage to the accumulator end.
16. Hand-tighten the accumulator pressure clamp bolt. Make sure the clamp is level and the tube is square to the end of the accumulator.
17. Place a shop cloth next to the opening of the inlet port adapter in order to capture any fluid exiting the hydro-boost unit.
Important:
Do not exceed 65 N.m (48 lb-ft) torque.
Important:
A torque wrench must be used to tighten the fixture clamp bolt
18. Slowly tighten the fixture clamp bolt while monitoring the inlet port adapter tube for signs of power steering fluid. Stop tightening of the bolt when either fluid is observed (below the maximum 65 N.m (48 lb-ft) torque) OR The 65 N.m (48 lb-ft) maximum bolt torque is achieved (with no fluid visible in the clear adapter tube). If fluid is seen coming out of the inlet port adapter up to 65 Nm (48 lb-ft) maximum torque, the hydro-boost booster assembly is "OK", Proceed to Step 19.
A. If NO fluid is seen exiting from the inlet port adapter, complete Steps 19-27 and then repeat Steps 1-18.
B. If no fluid is visible from the second evaluation, replace the hydro-boost unit. Proceed to the appropriate procedure found in this bulletin.
19. Loosen the clamp bolt, remove the clamp containment bolt, and remove the accumulator pressure clamp. Remove the inlet port adapter from the supply port of the booster. Wipe the excess power steering fluid off of the adapter with a clean, lint-free shop cloth. Store the adapter in a clean location, such as a plastic bag.
20. Reinstall the supply hose/tube to the booster.
Tighten
Tighten to 28 N.m (21 lb-ft).
21. Clean any spilled fluid from the outside of the booster.
22. For Express/Savana only:
^ Connect the reservoir outlet hose to the booster unit. Keeping the hose end higher than reservoir, reposition the reservoir onto the mounting studs.
A. Install the remote power steering reservoir mounting nuts.
Tighten
Tighten to 7 Nm (58 lb in).
23. Start the engine and run at idle. Depress the brake pedal 5 times. Turn the steering wheel to the "steering lock" position. Hold for 1-2 seconds. Check to see if there is any leakage from the ports/fittings.
24. Turn the engine off.
25. If leaks were observed, re-check that the fittings are at the recommended torque values. Repeat Steps 17 and 18.
26. Check the power steering reservoir fluid level, add fluid if necessary.
27. Close the hood.
Hydro-Boost(R) Replacement - Avalanche, Express, Savana, Silverado, Sierra, Suburban, Yukon XL
Tools Required
^ J 35555 Metal Mityvac
^ J 43485 Power Steering Bleeder Adapter
Removal
1. Apply the park brake and block the wheels.
2. Remove the master cylinder from the booster. Do not remove the pipes from the master cylinder. Set the master cylinder aside in the engine compartment.
3. Disconnect the power brake booster inlet hose, the steering gear inlet hose, and the power brake booster outlet hose from the booster assembly.
4. Disconnect the electrical connector from the stop lamp switch.
5. Remove the retainer from the brake pedal pin.
6. Remove the stop lamp switch and the pushrod to the power brake booster from the brake pedal pin.
7. Unsnap the stop lamp switch from the power brake booster pushrod.
8. Remove the 4 booster to bulkhead nuts.
9. Remove the booster assembly.
10. Remove the gasket.
Installation
1. Install the gasket.
2. Install the booster assembly.
3. Install the 4 booster to bulkhead nuts.
Tighten
Tighten the nuts to 36 N.m (26 lb-ft).
4. Snap the stop lamp switch onto the pushrod to the power brake booster.
5. Install the stop lamp switch with the pushrod on the brake pedal pin.
6. Install the brake switch retainer.
7. Connect the electrical connector to the stop lamp switch.
8. Install the master cylinder to the booster.
9. Install the master cylinder mounting nuts.
Tighten
Tighten the nuts to 36 N.m (27 lb-ft).
10. Connect the power brake booster outlet hose, the steering gear inlet hose, and the power brake booster inlet hose.
Tighten
^ Tighten the power brake booster inlet hose to 28 N.m (20 lb-ft).
^ Tighten the steering gear inlet hose to 28 N.m (20 lb-ft).
Important:
Maintain the fluid level throughout the bleed procedure.
11. Remove the pump reservoir cap.
Important:
Use clean, new power steering fluid only.
12. Fill the pump reservoir with fluid to the FULL COLD level.
13. Attach J 43485, Power Steering Bleeder Adapter, to J 35555, Metal Mityvac, or equivalent.
14. Place J 43485 on or in the pump reservoir filler neck.
15. Apply a vacuum of 68 kPa (20 in Hg) maximum.
16. Wait 1 minute.
17. Remove J 43485 and J 35555.
18. Reinstall the pump reservoir cap.
19. Start the engine. Allow the engine to idle.
20. Turn the steering wheel 180-360 degrees in both directions 5 times.
21. Switch the ignition off
22. Verify the fluid level.
23. Release the park brake and unblock the wheels.
Hydro-Boost(R) Replacement -- Kodiak, TopKick
Tools Required
^ J 35555 Metal Mityvac
^ J 43485 Power Steering Bleeder Adapter
Removal
1. Block the wheels.
2. Disconnect the electrical connectors from the electrohydraulic pump and the flow switch.
3. Remove the master cylinder nuts. Do not remove the pipes from the master cylinder. Position the master cylinder away from the booster head. Secure the master cylinder in an upright position.
4. Disconnect the power brake booster inlet hose, the steering gear inlet hose, and the power brake booster outlet hose from the booster assembly.
5. Remove the booster pump rod retainer from the lever.
6. Remove the stop lamp switch from the lever.
7. Remove the booster pump rod from the lever.
8. Remove the nuts at the booster.
9. Remove the booster assembly.
Installation
1. Install the booster assembly to the vehicle.
2. Install the nuts at the booster.
Tighten
Tighten the nuts to 50 N.m (37 lb-ft).
3. Install the booster pump rod to the lever.
4. Install the stop lamp switch to the lever.
5. Install the booster pump rod retainer.
6. Connect the power brake booster outlet hose, the steering gear inlet hose, and the power brake booster inlet hose.
Tighten
^ Tighten the power brake booster inlet hose to 28 N.m (20 lb-ft).
^ Tighten the steering gear inlet hose to 28 N.m (20 lb-ft).
7. Install the master cylinder.
8. Install the mounting nuts.
Tighten
Tighten the mounting bolts to 50 Nm (37 lb-ft).
9. Install the electrical connectors to the electrohydraulic pump and the flow switch.
10. Fill the hydraulic pump reservoir.
Important:
Maintain the fluid level throughout the bleed procedure.
11. Remove the pump reservoir cap.
Important:
Use clean, new power steering fluid only.
12. Fill the pump reservoir with fluid to the FULL COLD level.
13. Attach J 43485, Power Steering Bleeder Adapter, to J 35555, Metal Mityvac, or equivalent.
14. Place J 43485 on or in the pump reservoir filler neck.
15. Apply a vacuum of 68 kpa (20 in Hg) maximum.
16. Wait 1 minute.
17. Remove 1 J43485 and J 35555.
18. Reinstall the pump reservoir cap.
19. Start the engine. Allow the engine to idle.
20. Turn the steering wheel 180-360 degrees in both directions 5 times.
21. Switch the ignition off
22. Verify the fluid level.
23. Release the park brake and unblock the wheels.