GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Master Cylinder

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REMOVAL & INSTALLATION



Standard-Type

See Figures 1 through 6

  1. Disconnect the negative battery cable.
  2.  
  3. Using a suitable tool, drain some of the fluid from the master cylinder.
  4.  



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Fig. Fig. 1: To avoid spillage, use a clean turkey baster or similar tool to drain some of the fluid from the master cylinder before removal

  1. Unplug the fluid level sensor connector.
  2.  
  3. Disconnect and plug the brake lines from the master cylinder.
  4.  



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Fig. Fig. 2: After disconnecting the brake lines, be sure to plug them to prevent contaminants from entering the brake hydraulic system



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Fig. Fig. 3: Using a back-up wrench, unfasten the lines from the proportioning valve and ...



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Fig. Fig. 4: ... don't forget to plug the lines!

  1. Unfasten the nuts attaching the master cylinder to the power booster.
  2.  



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Fig. Fig. 5: Unfasten the master cylinder-to-power brake booster retaining nuts, then ...



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Fig. Fig. 6: ... remove the master cylinder assembly from the engine compartment

  1. Remove the master cylinder from its mounting studs and from the vehicle.
  2.  
  3. If necessary, unfasten the retaining roll pins and remove the fluid reservoir from the cylinder.
  4.  

To install:
  1. Replace the reservoir O-rings and bench bleed the master cylinder.
  2.  
  3. Position the master cylinder to the booster, then install the retaining nuts.
  4.  
  5. Unplug and fasten the brake lines to the master cylinder.
  6.  
  7. Attach the brake fluid level sensor electrical connector.
  8.  
  9. Fill the reservoir with brake fluid, then properly bleed the hydraulic system.
  10.  
  11. Connect the negative battery cable, then check the brakes for proper operation.
  12.  

ABS-Type

See Figure 7

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Fig. Fig. 7: View of the master cylinder assembly/ABS hydraulic modulator-1995-98 vehicles shown

When the ABS modulator cylinder pistons are in their uppermost position, each motor has prevailing torque due to the force necessary to ensure each piston is held firmly at the top of its travel. This torque results in "gear tension," or force on each gear that makes motor pack separation difficult. To avoid injury, or damage to the gears, the "Gear Tension Relief Sequence" (performed by GM's Tech 1 scan tool) briefly reverses each motor to eliminate the prevailing torque.

On ABS-equipped vehicles, the Hydraulic Modulator is mounted directly to the master cylinder; they must be removed as an assembly.


CAUTION
A Tech Iscan tool (or equivalent) is required to relieve the gear tension in the hydraulic modulator. This procedure must be performed prior to removal of the brake control and motor assembly. Attempting to remove the master cylinder without relieving the gear tension can cause personal injury.

  1. Make sure the ignition switch is in the OFF position.
  2.  
  3. Install the Tech 1 or equivalent with the correct chassis cartridge.
  4.  
  5. Turn the ignition switch to the ON position, leaving the engine OFF.
  6.  
  7. Select the proper function. The "Gear Tension Relief Sequence" is F5 on the Tech 1 scan tool.
  8.  

It should be noted that a scan tool is also needed to bleed the system after repairs to the ABS hydraulic system.

  1. Disconnect the negative battery cable.
  2.  
  3. Disengage the two solenoid electrical connectors and the fluid level sensor connector.
  4.  
  5. Detach the 6-pin and 3-pin motor pack electrical connectors.
  6.  
  7. Wrap a shop towel around the hydraulic brake lines, then disconnect the four brake lines from the modulator. Take care not to allow brake fluid to enter the bottom of the motor pack or electrical connections.
  8.  

Cap the disconnected lines to prevent the loss of fluid and the entry of moisture and contaminants.

  1. Unfasten the 2 nuts attaching the master cylinder assembly/ABS hydraulic modulator to the vacuum booster.
  2.  
  3. Remove the master cylinder assembly/ABS hydraulic modulator assembly from the vehicle.
  4.  

To install:
  1. Install the ABS hydraulic modulator assembly to the vehicle. Secure using the two attaching nuts and tighten to 20 ft. lbs. (27 Nm).
  2.  
  3. Uncap and connect the 4 brake pipes to the modulator assembly. Tighten to 13 ft. lbs. (17 Nm).
  4.  
  5. Attach the 6-pin and 3-pin electrical connectors.
  6.  
  7. Engage the fluid level sensor connector.
  8.  
  9. Properly bleed the brake system, as outlined later in this section.
  10.  
  11. Connect the negative battery cable.
  12.  

 
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