Yamaha YZF-R125 Service Manual: Bleeding the hydraulic brake system

WARNING

Bleed the hydraulic brake system whenever:

  • the system is disassembled.
  • a brake hose is loosened, disconnected or replaced.
  • the brake fluid level is very low.
  • brake operation is faulty.

NOTE:

  • Be careful not to spill any brake fluid or allow the brake master cylinder reservoir or brake fluid reservoir to overflow.
  • When bleeding the hydraulic brake system, make sure there is always enough brake fluid before applying the brake. Ignoring this precaution could allow air to enter the hydraulic brake system, considerably lengthening the bleeding procedure.
  • If bleeding is difficult, it may be necessary to let the brake fluid settle for a few hours. Repeat the bleeding procedure when the tiny bubbles in the hose have disappeared.

1. Bleed:

  • Hydraulic brake system

a. Fill the brake fluid reservoir to the proper level with the recommended brake fluid.

b. Install the diaphragm (brake master cylinder reservoir or brake fluid reservoir).

c. Connect a clear plastic hose "1" tightly to the bleed screw "2".

Bleeding the hydraulic brake system


A. Front

B. Rear

d. Place the other end of the hose into a container.

e. Slowly apply the brake several times.

f. Fully pull the brake lever or fully press down the brake pedal and hold it in position.

g. Loosen the bleed screw.

NOTE:

Loosening the bleed screw will release the pressure and cause the brake lever to contact the throttle grip or the brake pedal to fully extend.

h. Tighten the bleed screw and then release the brake lever or brake pedal.

i. Repeat steps (e) to (h) until all of the air bubbles have disappeared from the brake fluid in the plastic hose.

j. Tighten the bleed screw to specification.


k. Fill the brake fluid reservoir to the proper level with the recommended brake fluid.

Refer to "CHECKING THE BRAKE FLUID LEVEL" on page 3-18.

WARNING

After bleeding the hydraulic brake system, check the brake operation.

    Checking the rear brake hose
    1. Check: Brake hoses "1" Cracks/damage/wear  Replace. 2. Check: Brake hose holder "2" Loose connection Tighten the holder bolt. Loose or open holder Fasten properly ...

    Adjusting the drive chain slack
    NOTE: The drive chain slack must be checked at the tightest point on the chain. CAUTION:A drive chain that is too tight will overload the engine and other vital parts, and one that ...

    Other materials:

    Installing the rear brake master cylinder
    1. Install: Copper washers "1" Brake hose "2" Rear brake light switch "3" WARNINGProper brake hose routing is essential to insure safe vehicle operation. Refer to "CABLE ROUTING" on page 2-33. CAUTION:When installing the brake hose onto the brake master ...

    Removing the handlebars
    1. Stand the vehicle on a level surface. WARNINGSecurely support the vehicle so that there is no danger of it falling over. 2. Remove: Handlebar grip "1" NOTE: Blow compressed air between the handlebar and the handlebar grip, and gradually push the grip off the handleb ...

    Removing the throttle body
    1. Extract the fuel in the fuel tank through the fuel tank filler hole with a pump. 2. Disconnect: Fuel hose WARNINGCover the fuel hose connections with a cloth when disconnecting them. Residual pressure in the fuel lines could cause fuel to spurt out when removing the h ...

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