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Home >> Subaru >> 2022 >> Forester Wilderness >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> Brake System >> Air Bleeding >> Procedure >> Master Cylinder

Master Cylinder

NOTE:
  • When the master cylinder assembly is replaced or the oil reservoir COMPL is empty, bleed the brake master cylinder.
  • If air bleeding operation of the master cylinder assembly is not necessary, omit the following procedures, and perform air bleeding of the brake line. Ref. to BRAKE>AIR BLEEDING>PROCEDURE>BRAKE LINE .
  1. Remove the fuse (a) of electric brake booster from the main fuse box. (Electric brake booster model)
    NOTE: This operation is not required if the ground terminal is already removed from the battery sensor.
    G14385231Courtesy of SUBARU OF AMERICA, INC.
  2. Install the brake pipe to the master cylinder assembly.
    1. Screw and tighten the flare nut (b) so that the end of the nut contacts the back side of the brake pipe flare, while pressing the brake pipe (a) toward the master cylinder assembly side.
    CAUTION: Be careful not to make scratches or other damage to the inside surface of the brake pipe flare.
    G13199763Courtesy of SUBARU OF AMERICA, INC.

    Preparation tool: 

    Flare nut wrench

    Crowfoot wrench

    NOTE: If the work can be performed with the front and back sides reversed, it is also possible to use a 6-point crowfoot wrench.

    Tightening torque: 

    Calculation formula
    T = 19 N.m (1.9 kgf-m, 14.0 ft-lb) x L1/(L1 + L2)
    T: Reading of the torque wrench
    L1: Effective length of the torque wrench
    L2: Effective length of the crowfoot wrench
    NOTE: If the effective length of the tool used is unknown, consult the manufacturer of the tool.
    G14385236Courtesy of SUBARU OF AMERICA, INC.
  3. Fill the oil reservoir COMPL of the master cylinder assembly with brake fluid.
    NOTE:
    • Replenish brake fluid to the MAX level.
    • During the operation, keep the oil reservoir COMPL filled with brake fluid at MIN level or higher to prevent entry of air.
  4. Attach a transparent vinyl tube to the bleeder screw of the right front caliper body that is the closest from the hydraulic unit assembly VDC, and the other end of the vinyl tube to a collection container.
  5. Loosen the bleeder screw, depress the brake pedal slowly and hold it.
  6. Tighten the bleeder screw, and release the brake pedal quickly.
  7. Repeat steps  5 and  6 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.
  8. 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.
  9. Repeat steps  5 and  6 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 hydraulic control unit.
  10. 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.
  11. 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 hydraulic unit assembly VDC reaches the bleeder screw of the left rear caliper body assembly and is discharged.
  12. 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.
  13. Perform step  11.
    NOTE:
    • By repeating the procedures 10 times or more, air that entered in the rear brake pipe passages from the hydraulic unit assembly VDC reaches the bleeder screw of the right rear caliper body and is discharged.
    • With the procedures so far, bleed is completed for the air that entered in the rear brake piping hose passages and rear caliper from the hydraulic control unit. Lastly, perform the following procedures to bleed air that may remain in areas where the brake fluid flow stands.
  14. 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.
  15. After repeating firmly depressing of the brake pedal quickly 5 to 6 times, depress and hold the pedal.
  16. 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.
  17. Repeat steps  15 and  16 until there are no more air bubbles in the transparent vinyl tube.
    NOTE: Repeat the procedures approximately four to five times.
  18. Repeat steps  15 to  17 above for each brake caliper.
    NOTE: Bleed air in the order starting from the front RH → front LH → rear LH → rear RH.
  19. 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)

  20. Install the bleeder cap to each bleeder screw.
  21. Install the fuse (a) of electric brake booster. (Electric brake booster model)
    NOTE: Perform this operation only when the fuse of electric brake booster is removed.
    G14385231Courtesy of SUBARU OF AMERICA, INC.
  22. Check that the electric brake booster operates normally. (Electric brake booster model)
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