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Master Cylinder

WARNING: This page is about a different car, the 2022 Subaru WRX. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
  • During the operation, remove the fuse of electric brake booster from the sub fuse box to prevent the electric brake booster from starting. (Electric brake booster model) 
  • Do not let brake fluid come into contact with the painted surface of the vehicle. Wash away with water immediately and wipe off if it is spilled by accident. 
  • Do not mix different kinds of brake fluid. 
  • Do not allow water or foreign matter to enter the reservoir tank. 
  • Always use new brake fluid when replacing or refilling the brake fluid. 
  • 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 the brake fluid around each bleeder screw and the reservoir tank. 
NOTE:
  • When the master cylinder assembly is replaced or the reservoir tank is empty, bleed air from the brake master cylinder and the clutch master cylinder (MT model). For air bleeding of the clutch system, refer to "Air Bleeding" in "CLUTCH SYSTEM". Ref. to  CLUTCH SYSTEM>AIR BLEEDING>PROCEDURE  . 
  • 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  . 
  • For convenience and safety, perform the work with 2 people. 
  1. Remove the fuse (a) of electric brake booster from the sub fuse box. (Electric brake booster model)
    NOTE:

    This operation is not required if the ground terminal is already removed from the battery sensor. 

    G14602282Courtesy of SUBARU OF AMERICA, INC.
  2. 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 and a 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. 

    G13199763Courtesy of SUBARU OF AMERICA, INC.

    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. 

    G14602287Courtesy of SUBARU OF AMERICA, INC.
  3. Add the brake fluid to the "MAX".
  4. Connect a transparent vinyl tube, etc. to the bleeder screw of the right front caliper body, 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 tube.
    NOTE:

    Air bubbles are removed after repeating the procedures six to seven times. 

  8. Connect a transparent vinyl tube to the bleeder screw of the left front caliper body, and the other end of the vinyl tube to a collection container.
  9. Repeat steps  5 and  6 until there are no more air bubbles in the brake fluid in the 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 & H/U.
  10. Connect a transparent vinyl tube to the bleeder screw of the left rear caliper body, and the other end of the vinyl tube to a 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 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 & H/U reaches the bleeder screw of the left rear caliper body and is discharged. 

  12. Connect a transparent vinyl tube to the bleeder screw of the right rear caliper body, and the other end of the vinyl tube to a 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 VDC Control Module & 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 & H/U is completed. Lastly, perform the following procedures to bleed air that may remain in areas where the brake fluid flow stands. 
  14. Connect a transparent vinyl tube, etc. to the bleeder screw of the right front caliper body, and the other end of the vinyl tube to a 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 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 each bleeder screw to the specified torque.

    Tightening torque: 

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

    Rear (except for the electronic parking brake model): 8 N.m (0.8 kgf-m, 5.9 ft-lb)

    Rear (electronic parking brake model): 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. 

    G14602282Courtesy of SUBARU OF AMERICA, INC.
  22. Check that the electric brake booster operates normally. (Electric brake booster model)
  23. Check that there are no brake fluid leaks at the flare nut portion or in the entire brake system.
  24. After inspection, wipe off the brake fluid around each bleeder screw and the reservoir tank.
  25. Perform a road test and ensure that the brakes operate normally.
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