Lexus GS, SC 1998-06

Hydraulic Brake Booster

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Removal & Installation



  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Disconnect the negative battery cable.
    NOTE
    Before starting the work, make sure that the ignition switch is OFF and depress the brake pedal more than 40 times. As high pressure is applied to the brake actuator tube No. 1, never deform it. Until the work is over, do not turn the ignition switch ON.

  4.  
  5. Draw out brake fluid with syringe. Wash brake fluid off immediately if it adheres to any painted surfaces.
  6.  
  7. Remove the No. 1 under cover.
  8.  
  9. Remove the end pad and the No. 1 safety pad.
  10.  
  11. Remove the No. 7 heater to register duct.
  12.  
  13. Disconnect the 4 brake lines.
  14.  
  15. Disconnect the left front wheel brake line from the flexible hose.
  16.  
  17. Remove the 2 brake line clamps
  18.  
  19. Disconnect the level warning switch connector.
  20.  
  21. Disconnect the 4 connectors.
  22.  
  23. Remove the pedal return spring, clip and clevis pin.
  24.  
  25. Loosen the lock nut, then remove the clevis and lock nut.
  26.  
  27. Remove the 4 booster installation nuts.
  28.  
  29. Remove the hydraulic brake booster assembly and gasket.
  30.  

To install:

  1. Install the hydraulic brake booster assembly and gasket. Install the 4 nuts and tighten them to 9 ft. lbs. (13 Nm).
  2.  
  3. Install the clevis and lock nut. Tighten the lock nut to 19 ft. lbs. (25 Nm).
  4.  
  5. Install the pedal return spring.
  6.  
  7. Connect the 4 connectors.
  8.  
  9. Connect the level warning switch connector.
  10.  
  11. Install the 2 brake line clamps
  12.  
  13. Connect the left front wheel brake line to the flexible hose and tighten to 11 ft. lbs. (15 Nm).
  14.  
  15. Connect the 4 brake lines to the hydraulic brake booster. Tighten the fittings to 11 ft. lbs. (15 Nm).
  16.  
  17. Install the No. 7 heater to register duct.
  18.  
  19. Install the end pad and the No. 1 safety pad.
  20.  
  21. Install the No. 1 under cover.
  22.  
  23. Fill the reservoir with brake fluid.
  24.  
  25. Connect the negative battery cable.
  26.  
  27. Bleed the brake system.
  28.  
  29. Check for brake fluid leaks.
  30.  



Click image to see an enlarged view

Fig. Exploded view of the master cylinder/hydraulic brake booster assembly.-SC 430

  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Disconnect the negative battery cable.
    NOTE
    Before starting the work, make sure that the ignition switch is OFF and depress the brake pedal more than 40 times. As high pressure is applied to the brake actuator tube No. 1, never deform it. Until the work is over, do not turn the ignition switch ON. When the power supply system-s pressure is released, the pedal resistance decreases.

  4.  
  5. Drain the brake fluid. Wash off brake fluid immediately if it comes in contact with any painted surface.
  6.  
  7. Remove the V-bank cover.
  8.  
  9. Remove the brake master cylinder cover assembly.
  10.  
  11. Remove the instrument panel safety pad.
  12.  
  13. Remove the brake pedal return spring, clip and push rod pin.
  14.  
  15. Remove the left front wheel.
  16.  
  17. Disconnect the 4 brake lines from the master cylinder (hydraulic brake booster).
  18.  
  19. Attach identification tags to the lines or write down line connection locations so that the lines can be reconnected correctly.
  20.  
  21. Disconnect the left front brake line from the flexible hose.
  22.  
  23. Disconnect the 5 connectors and harness clamp from the master cylinder.
  24.  
  25. Remove the 2 nuts and disconnect the brake lines from the vehicle body.
  26.  
  27. Remove the 4 nuts and pull out the master cylinder.
  28.  
  29. Remove the gasket from the master cylinder.
  30.  
  31. Remove the brake booster pump assembly from the master cylinder.
  32.  
  33. Remove the brake booster accumulator assembly from the master cylinder.
  34.  

To install:

  1. Install the accumulator pipe, compression spring and new O-ring. Keep the pump free from foreign matter.
  2.  
  3. Using SST 09318-12010, install the accumulator. Tighten the screws to 36 ft. lbs. (54 Nm).
  4.  
  5. Install the brake booster pump assembly.
  6.  
  7. Instal a new gasket to the master cylinder.
  8.  
  9. Install the master cylinder with the 4 nuts and tighten to 11 ft. lbs. (15 Nm).
  10.  
  11. Install the brake lines to the vehicle body with the 2 nuts and tighten to 43 inch lbs. (4.9 Nm).
  12.  
  13. Connect the front brake line to the flexible hose. Tighten to 11 ft. lbs. (15 Nm) without SST, or 10 ft. lbs. (14 Nm) with SST.
  14.  
  15. Connect each brake line to the correct position of the master cylinder. Tighten to 11 ft. lbs. (15 Nm) without SST, or 10 ft. lbs. (14 Nm) with SST.
  16.  
  17. Connect the 5 connectors and harness clamp to the master cylinder.
  18.  
  19. Install the push rod pin and the clip.
  20.  
  21. Install the brake pedal return spring.
  22.  
  23. Install the instrument panel safety pad.
  24.  
  25. Install the brake master cylinder cover assembly.
  26.  
  27. Install the V-bank cover.
  28.  
  29. Fill the reservoir with brake fluid.
  30.  
  31. Bleed the brake system.

    Click image to see an enlarged view

    Fig. Measuring brake pedal height.-SC 430

  32.  
  33. Check and adjust brake pedal height as follows:


    1. Check brake pedal height. Pedal height from asphalt sheet: 154.0 to 164.0mm (6.063 to 6.457 in.)
    2.  
    3. Remove the instrument finish panel lower.
    4.  
    5. Disconnect the connector from the stop lamp switch.
    6.  
    7. Loosen the switch lock nut and remove the switch.
    8.  
    9. Loosen the clevis lock nut.
    10.  
    11. Adjust the pedal height by turning the pedal push rod.
    12.  
    13. Tighten the push rod lock nut to 19 ft. lbs. (26 Nm).
    14.  
    15. Install the switch.
    16.  
    17. Connect the connector to the switch.
    18.  
    19. Depress the pedal 5 to 15mm (0.20 to 0.59 in.). Rotate the switch until the stop lamps illuminate. Then tighten the lock nut.
    20.  
    21. After the installation, depress the pedal 5 to 15mm (0.20 to 0.59 in.), and check that the stop lamps illuminate.

      Click image to see an enlarged view

      Fig. Measuring pedal free play.-SC 430

    22.  

  34.  
  35. Check pedal free play as follows:


    1. Stop the engine. Depress the pedal several times until there is no vacuum in the booster. Then release the pedal.
    2.  
    3. Depress the pedal until resistance is felt.
    4.  
    5. Check the pedal-s free play by measuring the distance between the position in (b) and the pedal-s released position. Pedal free play: 0.2 to 2.0mm (0.008 to 0.079 in.)
    6.  
    7. If the free play is not as specified, proceed to the next step. If the free play is as specified, proceed to the pedal reserve distance procedure.
    8.  
    9. Check the stop lamp switch clearance. Stop lamp switch clearance: 0.5 to 2.4mm (0.020 to 0.094 in.)
    10.  
    11. If the clearance is not as specified, adjust the clearance and recheck the pedal-s free play.
    12.  
    13. If the clearance is as specified, troubleshoot the brake system and proceed to pedal reserve distance procedure.

      Click image to see an enlarged view

      Fig. Measuring pedal reserve distance.-SC 430

    14.  

  36.  
  37. Check pedal reserve distance as follows:


    1. Release the parking brake lever. Start the engine.
    2.  
    3. Depress the pedal and check the pedal reserve distance.
    4.  
    5. Depress the pedal with a force of 44.1 lbs. (196 N).
    6.  
    7. Measure the distance between the pedal and asphalt sheet shown in the illustration. Pedal reserve distance: More than 100 mm (3.94 in.)
    8.  
    9. If the distance is not as specified, troubleshoot the brake system.
    10.  

  38.  
  39. Check fluid level in reservoir.
  40.  
  41. Check for brake fluid leakage.
  42.  
  43. Connect the negative battery cable.
  44.  
  45. Install the left front wheel.
  46.  
  47. Check brake master cylinder operation.
  48.  

 
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