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Home >> Subaru >> 2021 >> Outback Base >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> Brake System >> Air Bleeding >> Procedure >> Master Cylinder

Master Cylinder

CAUTION:
  • Do not let brake fluid come into contact with the painted surface of the vehicle body. Wash away with water immediately and wipe off if it is spilled by accident.
  • Avoid mixing brake fluid of different brands or different grades even from the same brand to prevent fluid performance from degrading.
  • When refilling brake fluid, do not allow dirt or dust to get into the reservoir tank.
  • Always use new SUBARU genuine brake fluid when replacing or refilling the fluid. Do not reuse drained brake fluid.
  • For convenience and safety, perform the work with 2 people.
  • During the operation, keep the reservoir tank filled with brake fluid at MIN level or higher to prevent entry of air.
  • After air bleeding operation, wipe off fluid around each bleeder screw and the reservoir tank.
NOTE:
  • When the master cylinder assembly is replaced or the reservoir tank is empty, bleed the brake master cylinder.
  • If bleeding of the master cylinder assembly is not necessary, omit the following procedures, and perform bleeding of the brake line. Ref. to BRAKE>AIR BLEEDING>PROCEDURE>BRAKE LINE .
  1. Install the brake pipe to the master cylinder assembly.
    CAUTION: Be careful not to make scratches or other damage to the inside surface of the brake pipe flare.
    1. Turn and tighten the flare nut (b) by hand while pressing the brake pipe (a) toward the master cylinder assembly side.
    2. Tighten the flare nut (b) using a flare nut wrench.

      Tightening torque: 

      19 N-m (1.9 kgf-m, 14.0 ft-lb)

    G13950116Courtesy of SUBARU OF AMERICA, INC.
  2. Fill the reservoir tank of the master cylinder assembly with brake fluid.
    NOTE:
    • Replenish brake fluid to the MAX level.
    • During the operation, keep the reservoir tank filled with brake fluid at MIN level or higher to prevent entry of air.
  3. Attach a transparent vinyl tube to the bleeder screw of the right front caliper body that is the closest from the VDC control module and H/U, and attach the other end of the vinyl tube to a collection container.
  4. Loosen the bleeder screw, depress the brake pedal slowly and hold it.
  5. Tighten the bleeder screw, and release the brake pedal quickly.
  6. Repeat steps  4 ) and  5 ) until there are no more air bubbles in the brake fluid in the vinyl tube.
    NOTE: Air bubbles are removed after repeating the procedures six to seven times.
  7. Attach a transparent vinyl tube to the bleeder screw of the left front caliper body, and the other end of the vinyl tube to a brake fluid collection container.
  8. Repeat steps  4 ) and  5 ) until there are no more air bubbles in the brake fluid in the vinyl tube.
    NOTE:
    • Air bubbles are removed after repeating the procedures seven to eight times.
    • With the procedures so far, bleed is completed for the air that entered in the master cylinder, front brake piping hose passages and front caliper.

    Next, perform the following procedures to bleed air that entered in the rear brake piping hose passages and rear caliper from the VDC control module and H/U.
  9. Attach a transparent vinyl tube to the bleeder screw of the left rear caliper body, and the other end of the vinyl tube to a brake fluid collection container.
  10. Loosen the bleeder screw, and repeat the full stroke depressing operation of the brake pedal slowly, until the brake fluid in the transparent vinyl tube has no more air bubbles, then tighten the bleeder screw.
    NOTE: By repeating the procedures 15 times or more, air that entered in the rear brake pipe passages from the VDC control module and H/U reaches the bleeder screw of the left rear caliper body and is discharged.
  11. Attach a transparent vinyl tube to the bleeder screw of the right rear caliper body, and the other end of the vinyl tube to a brake fluid collection container.
  12. Perform step 10).
    NOTE:
    • By repeating the procedures 10 times or more, air that entered in the rear brake pipe passages from the VDC control module and H/U reaches the bleeder screw of the right rear caliper body and is discharged.
    • With the procedures so far, bleeding of the air that entered in the rear brake piping hose passages and rear caliper from the VDC control module and H/U is completed. Lastly, perform the following procedures to bleed air that may remain in areas where the brake fluid flow stands.
  13. Attach a transparent vinyl tube to the bleeder screw of the right front caliper body, and the other end of the vinyl tube to a brake fluid collection container.
  14. After repeating firmly depressing of the brake pedal quickly five or six times, depress and hold the pedal.
  15. Loosen the bleeder screw to drain brake fluid. When the brake pedal reaches the full stroke position, tighten the bleeder screw quickly, and release the brake pedal.
  16. Repeat steps  14 ) and  15 ) until there are no more air bubbles in the transparent vinyl tube.
    NOTE: Repeat the procedures approximately four to five times.
  17. Repeat steps  14 ) to  16 ) above for each brake caliper.
    NOTE: Bleed air in the order starting from the front RH>front LH>rear LH>rear RH.
  18. Tighten the bleeder screw to the specified torque.

    Tightening torque: 

    Front: 8 N-m (0.8 kgf-m, 5.9 ft-lb)

    Rear: 17 N-m (1.7 kgf-m, 12.5 ft-lb)

  19. Install the bleeder cap to each bleeder screw.
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