Subaru Legacy BN/BS (2015-2019) Service Manual: Air bleeding procedure
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. • Do not reuse drained brake fluid. When refilling brake fluid, always refill new brake fluid. • Do not allow dirt or dust to get into the reservoir tank. • Do not mix two different kinds or makes of fluid to prevent fluid performance from degrading. • 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. For air bleed procedure of each part, refer to the following. • Master cylinder: Air Bleeding > PROCEDURE • Brake line: Air Bleeding > PROCEDURE • Hydraulic control unit: Air Bleeding > PROCEDURE • Caliper: Air Bleeding > PROCEDURE 1. MASTER CYLINDER For air bleed procedure of each part, refer to the following. • Master cylinder: Air Bleeding > PROCEDURE • Brake line: Air Bleeding > PROCEDURE • Hydraulic control unit: Air Bleeding > PROCEDURE • Caliper: Air Bleeding > PROCEDURE 1. 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. Tightening torque: Brake pipe flare nut: 19 N·m (1.9 kgf-m, 14.0 ft-lb)
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 assembly that is the closest from the VDC control module & hydraulic control unit, and 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 assembly, 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 hydraulic unit. 9. Attach a transparent vinyl tube to the bleeder - screw of the left rear caliper body assembly, 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 & hydraulic control unit reaches the bleeder - screw of the left rear caliper body assembly and is discharged. 11. Attach a transparent vinyl tube to the bleeder - screw of the right rear caliper body assembly, 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 & hydraulic control unit reaches the bleeder - screw of the right rear caliper body assembly 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 unit. 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 assembly, 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: Bleeder - screw: 8 N·m (0.82 kgf-m, 5.9 ft-lb) 2. BRAKE LINE 1. When the master cylinder assembly is replaced or the reservoir tank is empty, bleed the master cylinder assembly before bleeding the brake line. Air Bleeding > PROCEDURE 2. Fill the reservoir tank of the master cylinder assembly with brake fluid. NOTE: While bleeding air, keep the reservoir tank filled with brake fluid to prevent entry of air. 3. Attach one end of a transparent vinyl tube to the bleeder - screw, and the other end to a brake fluid collection container.
4. Loosen the bleeder - screw, and then repeat the full stroke depressing operation of the brake pedal, until brake fluid in the transparent vinyl tube has no more air bubbles. NOTE: Air bubbles are removed after repeating the depressing operation 15 times or more for the front caliper, and 20 times or more for the rear caliper. 5. Perform the steps 2) to 4) above on each brake caliper. NOTE: Perform in the order starting from the front RH > front LH > rear LH > rear RH. 6. Tighten the loosened bleeder - screw, repeat firmly depressing of the brake pedal 5 to 6 times, and then depress and hold the brake pedal. 7. Loosen the bleeder - screw to drain the brake fluid. When the brake pedal reaches the full stroke position, immediately tighten the bleeder - screw and return the brake pedal. 8. Repeat steps 6) and 7) until there are no more air bubbles in the transparent vinyl tube. 9. Perform the steps 6) to 8) above on each brake caliper. NOTE: Perform in the order starting from the front RH > front LH > rear LH > rear RH. 10. Operate the hydraulic control unit in the sequence control mode for both ABS and VDC systems. CAUTION: • If there is a possibility that air enters the pressure control section in the hydraulic control unit, perform steps 11) to 16). • For normal air bleeding operation, do not operate the sequence control for the hydraulic control unit. (Operating the sequence control may let air in the normal air bleeding passages move to the pressure control section.) NOTE: • Normal air bleeding operation does not help bleed air that enters the pressure control section in the hydraulic control unit. • If there is a possibility that air enters the pressure control section in the hydraulic control unit (if VDC or ABS operates with air contained in the normal air bleeding passage), perform the sequence control mode for both of the ABS and VDC systems. 11. Perform the ABS sequence control mode. ABS Sequence Control CAUTION: Be sure to perform the ABS sequence control mode first. 12. Perform the air bleeding operation of steps 3) and 4) for the bleeder - screw on each caliper. NOTE: • Perform in the order starting from the front RH > front LH > rear LH > rear RH. • As a reference, the number of the full stroke depressing operation is six times. 13. Perform the VDC sequence control mode. VDC Sequence Control 14. Perform the air bleeding operation of steps 3) and 4) for the bleeder - screw on each caliper. 15. Repeat from steps 11) to 14) for three cycles. 16. In case air still remains at step 15), repeat steps 11) to 14) again until all air is removed. 17. Fill the reservoir tank with brake fluid up to the “MAX” level. 18. Tighten the bleeder - screw to the specified torque. Tightening torque: Bleeder - screw: 8 N·m (0.82 kgf-m, 5.9 ft-lb) 19. Check that there are no brake fluid leaks at the flare nut portion or in the entire brake system. 20. Perform a road test and ensure that the brakes operate normally. 3. HYDRAULIC CONTROL UNIT 1. Bleed air from the brake line. Air Bleeding > PROCEDURE NOTE: If there is a possibility that air enters the pressure control section in the hydraulic control unit, perform the sequence control mode for both of the ABS and VDC systems. (Refer to steps 10) to 16) for brake lining.) 4. CALIPER 1. Bleed air from the brake line. Air Bleeding > PROCEDURE CAUTION: • For the caliper with electronic parking actuator, never drain the brake fluid in the caliper. • When removing the caliper with electronic parking actuator from the vehicle, make sure to apply the brake fluid seal before disconnection. • Do not remove the brake fluid seal of the caliper with replacement electronic parking actuator, except when the caliper is installed on the vehicle. |
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