It is necessary to bleed the hydraulic system any time the system has been opened or has trapped air within the fluid lines. It may be necessary to bleed the system at all four brakes if air has been introduced through a low fluid level or by disconnecting brake pipes at the master cylinder.
If a line is disconnected at one wheel only, generally only that brake needs bleeding. If lines are disconnected at any fitting between the master cylinder and the brake, the system served by the disconnected pipe must be bled.
See Figures 1, 2 and 3
If the master cylinder has been removed, the lines disconnected or the reservoir allowed to run dry, the cylinder must be bled before the lines are bled. To bleed the master cylinder:
- Check the level of the fluid in the reservoir. If necessary, fill with fluid.
- Disconnect the brake lines from the master cylinder. Plug the lines to keep dirt from entering.
- Place a pan or rags under the cylinder.
- Have an assistant slowly depress the brake pedal and hold it down.
- Block off the outlet ports with your fingers. Be sure to wear gloves. Have the assistant release the pedal. Make a tight seal with your fingers; do not allow the cylinder to ingest air when the pedal is released.
- Repeat three or four times.
- Connect the brake lines to the master cylinder and top up the fluid reservoir.
LINES AND WHEEL CIRCUITS
See Figure 4
- Insert a clear vinyl tube onto the bleeder plug at the wheel. If all four wheels are to be bled, begin with the right rear.
- Insert the other end of the tube into a jar which is half filled with brake fluid. Make sure the end is submerged in the fluid.
- Have an assistant slowly pump the brake pedal several times. On the last pump, have the assistant hold the pedal fully depressed. While the pedal is depressed, open the bleeder plug until fluid starts to run out, then close the plug.
If the brake pedal is pumped too fast, small air bubbles will form in the brake fluid which will be very difficult to remove.
- Repeat this procedure until no air bubbles are visible in the hose. Close the bleeder port.
Constantly replenish the brake fluid in the master cylinder reservoir, so that it does not run out during bleeding.
- If bleeding the entire system, repeat the procedure at the left rear wheel, the right front wheel and the left front wheel in that order.
- Bleed the load sensing proportioning and bypass valve.