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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 620 (POWER STEERING SYSTEM)REPAIR INSTRUCTIONSEXCESSIVE VACUUM DROP DIAGNOSIS
1999 GMC Forward Control 5.7 R, Automatic

Excessive Vacuum Drop Diagnosis

1999 GMC Forward Control 5.7 R, AutomaticSECTION Excessive Vacuum Drop Diagnosis
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
  1. If the vacuum continues to drop, remove the pressure and return hose from the pump.
  2. Install the plugs (1,2) supplied with the J 43485  into the pressure and return port.
    Fig 1: Installing Plugs Into Pressure And Return Port
    G01419050Courtesy of GENERAL MOTORS CORP.
  3. Attach the J 43485  to the J 35555  or equivalent.
  4. Place the J 43485  on or in the pump reservoir filler neck.
    Fig 2: Placing J 43485 On Or In Pump Reservoir Filler Neck
    G01419051Courtesy of GENERAL MOTORS CORP.
  5. Apply a vacuum of 68 kPa (20 in Hg) maximum.
  6. If the vacuum drops again, repair or replace the pump. If the vacuum holds steady, continue to check the other parts of the steering system.

    Important:  Fluid must be free from bubbles and foam. Be aware of periodic bubbles that indicate a loose connection or leaking O-ring seal in the return hose or the pressure hose.

    Fluid must be free from discoloration.

  7. Observe the fluid.
  8. If condition persists, replace the following parts:
    • The return hose clamps
    • The return hose O-rings
    • The pressure hose O-rings
    • The gear cylinder line O-rings
    • The reservoir to pump O-ring
  9. Repeat the bleed procedure from the beginning.
  10. Drive the vehicle approximately 16 km (10 mi) in order to warm the system to operating temperature. Evaluate vehicle on a smooth flat surface.
  11. Verify the following conditions:
    • There is smooth power assist.
    • The vehicle operates quietly.
    • The pump maintains the proper fluid level.
    • There is not any leaking in the steering system.
    • The fluid is free of foam or discoloration.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.