See Figures 1 and 2
The brake system is bled through the bleeder screws on the calipers and/or rear wheel cylinders. The system must be bled whenever air enters, whether due to disconnection of a hydraulic line or a leak. A spongy brake pedal indicates bleeding is needed even when no repairs have been made. Also check carefully for leaks and repair them as necessary.
Bleeding pumps fluid into the system via the master cylinder and bleeds air out through the bleed valves. You must keep the master cylinder reservoir full of fluid at all times to provide a continuous flow of airfree fluid into the system. You'll also need an assistant who will keep constant pressure on the brake pedal at all times to keep air from being drawn back into the system.
- Fill the master cylinder reservoir to the "MAX" line with brake fluid and keep it at least half full throughout the bleeding procedure.
If the master cylinder has been removed or disconnected, it must be bled before any brake unit is bled. To bleed the master cylinder:
- Disconnect the front brake line from the master cylinder and allow fluid to flow from the front connector port.
- Reconnect the line to the master cylinder and tighten it until it is fluid tight.
- Have a helper press the brake pedal down one time and hold it down.
- Loosen the front brake line connection at the master cylinder. This will allow trapped air to escape, along with some fluid. (Have a rag or small container handy to catch the fluid.)
- Again tighten the line, release the pedal slowly and repeat the sequence (Steps 2c, d, and e) until only fluid runs from the port. No air bubbles should be present in the fluid.
- Final tighten the line fitting at the master cylinder to 11 ft. lbs. (15 Nm).
- After all the air has been bled from the front connection, bleed the master cylinder at the rear connection by repeating Steps 2a through e.
- Start with the right rear brake caliper or wheel cylinder. Place the correct size box-end or line wrench over the bleeder valve and attach a tight-fitting transparent hose over the bleeder. Allow the tube to hang submerged in a transparent container of clean brake fluid. The fluid must remain above the end of the hose at all times, otherwise the system will ingest air instead of fluid.
- Have an assistant pump the brake pedal several times slowly and hold it down.
- Open the bleed point (about 1 / 4 - 1 / 2 turn is usually enough) and watch for bubbles in the brake fluid flow into the container. You must close the bleed valve before the brake pedal bottoms in its travel. Once the assistant has the feel of the pedal, he can warn you in advance. The more the bleed valve is opened, the quicker the pedal travels downward. With the bleed point closed, the assistant should release the pedal so the master cylinder will admit fresh, air-free fluid into the system. Once he has put pressure back on the pedal, you may re-open the bleed point, again closing it before the pedal bottoms out. Repeat this process until the fluid flowing from the bleed point is entirely air-free.
- After two or three bleedings, check and replenish the fluid in the reservoir.
- Repeat the process, in the correct order, at each remaining wheel. The general theory is to bleed the longest lines first and work towards the master cylinder-right rear, left rear, right front, left front.
- When all four wheels have been bled and no air is evident in the fluid, refill the master cylinder reservoir and attach the cap tightly.
VEHICES WITH LOAD SENSING PROPORTIONING VALVE
See Figure 3
After bleeding the right rear wheel, proceed to bleed the load sensing valve located on the frame at the rear of the vehicle. Next bleed the right front then left front. Use the bleeder fitting on the valve; do not attempt to loosen the lines entering the unit. Follow the bleeding procedure for normal systems and bleed the proportioning valve as you would any other cylinder or caliper.
VEHICLES WITH ABS
See Figure 4
After bleeding the master cylinder and the four wheels, bleed the brake lines going to the hydraulic unit or modulator unit. Start the engine before bleeding the brake system on vehicles with ABS. Otherwise the system for bleeding the brakes is identical to the system for vehicles without ABS.