The hydraulic brake system must be bled any time one of the lines is disconnected or any time air enters the system. If a point in the system, such as a wheel cylinder or caliper brake line is the only point which was opened, the bleeder screws down stream in the hydraulic system are the only ones which must be bled. If however, the master cylinder fittings are opened, or if the reservoir level drops sufficiently that air is drawn into the system, air must be bled from the entire hydraulic system. If the brake pedal feels spongy upon application, and goes almost to the floor but regains height when pumped, air has entered the system. If no fittings were recently opened for service, check for leaks that would have allowed the entry of air and repair them before attempting to bleed the system.
As a general rule, once the master cylinder is bled, the remainder of the hydraulic system should be bled starting at the furthest wheel from the master cylinder and working towards the nearest wheel. Therefore, the correct bleeding sequence is: master cylinder, right rear wheel cylinder, left rear, right front caliper and left front. Most master cylinder assemblies on these vehicles are NOT equipped with bleeder valves, therefore air must be bled from the cylinders using the front brake pipe connections.
See Figures 1, 2 and 3
For those of us who are not fortunate enough to have access to a power bleeding tool, the manual brake bleeding procedure will quite adequately remove air from the hydraulic system. The major difference between the pressure and manual bleeding procedures is that the manual method takes more time and will require help from an assistant. One person must depress the brake pedal, while another opens and closes the bleeder screws.
- Deplete the vacuum reserve by applying the brakes several times with the ignition OFF .
- Clean the top of the master cylinder, remove the cover and fill the reservoirs with clean fluid.
The master cylinder must be bled first if it is suspected to contain air. If the master cylinder was removed and bench bled before installation it must still be bled, but it should take less time and effort. Bleed the master cylinder as follows:
- Position a container under the master cylinder to catch the brake fluid.
- Loosen the front brake line(s) at the master cylinder and allow the fluid to flow from the front port.
- Tighten the line connection(s).
- Have an assistant depress and hold the brake pedal.
- Loosen the line connection(s) again, allowing air to escape from the master cylinder.
- Tighten the line(s), then have the assistant release the brake pedal and wait for 15 seconds.
- Repeat steps D through F until the line(s) are free of air.
- When finished bleeding the air from the master cylinder, tighten the line connections to 20 ft. lbs. (27 Nm).
- Repeat steps B through H, only with the master cylinder rear pipe fitting(s).
- Refill the master cylinder with fresh brake fluid.
If a single line or fitting was the only hydraulic line disconnected, then only the caliper(s) or wheel cylinder(s) affected by that line must be bled. If the master cylinder required bleeding, then all calipers and wheel cylinders must be bled in the proper sequence:
- Right rear
- Left rear
- Right front
- Left front
Bleed the individual calipers or wheel cylinders as follows:
- Place a suitable wrench over the bleeder screw and attach a clear plastic hose over the screw end. Be sure the hose is seated snugly on the screw or you may be squirted with brake fluid.
- Submerge the other end of the tube in a transparent container of clean brake fluid.
- With the help of an assistant, apply the brake pedal slowly and hold.
During the bleeding procedure, make sure your assistant does NOT release the brake pedal while a fitting is loosened or while a bleeder screw is opening. Air will be drawn back into the system.
- While the assistant continues to apply pressure to the brake pedal, loosen the bleeder screw, and watch for air bubbles in the container.
Be very careful when loosening the wheel cylinder and brake caliper bleeding screws. The bleeder screws often rust in position and may easily break off if forced. To help prevent the possibility of breaking a bleeder screw, spray it with some penetrating oil before attempting to loosen it. Installing a new bleeder screw will often require removal of the component and may include overhaul or replacement of the wheel cylinder/caliper.
- Tighten the bleeder screw.
- Instruct the assistant to release the brake pedal.
- Wait approximately 15 seconds, and instruct the assistant to depress the brake pedal again.
Remember, if the reservoir is allowed to empty of fluid during the procedure, air will be drawn into the system and the bleeding procedure must be restarted at the master cylinder assembly.
- Repeat steps C through F until there are no air bubbles present in the container.
- Check the pedal for a hard feeling with the engine not running. If the pedal is soft, repeat the bleeding procedure until a firm pedal is obtained.
- If the brake warning light is on, depress the brake pedal firmly. If there is no air in the system, the light will go out.
- Once all the air is bled from the system, install the bleeder screw caps.
- After bleeding, make sure that a firm pedal is achieved before attempting to move the vehicle.
For those who are fortunate enough to own or have access to a pressure bleeding tool, this procedure may be used to quickly and efficiently remove air from the brake system. This procedure may be used as a guide, but be careful to follow the tool manufacturer's directions closely. Any pressure bleeding tool MUST be of the diaphragm-type. A proper pressure bleeder tool will utilize a rubber diaphragm between the air source and brake fluid in order to prevent air, moisture oil and other contaminants from entering the system.
- Install Pressure Bleeder Adapter Cap J 35589 or equivalent, to the master cylinder.
- Charge Diaphragm Type Brake Bleeder J 29532 or equivalent, to 20-25 psi (140-172 kPa).
- Connect the line to the pressure bleeder adapter cap, then open the line valve.
- Raise and safely support the vehicle.
If it is necessary to bleed all of the calipers/cylinders, the following sequence should be used:
- Place a proper size box end wrench (or tool J 21472) over the caliper/cylinder bleeder valve.
- Attach a clear tube over the bleeder screw, then submerge the other end of the tube in a clear container partially filled with clean brake fluid.
- Open the bleeder screw at least 3 /4 of a turn and allow flow to continue until no air is seen in the fluid.
- Close the bleeder screw. Tighten the rear bleeder screws to 62 inch lbs. (7 Nm) and the front bleeder screws to 115 inch lbs. (13 Nm).
- Repeat Steps 6-9 until all of the calipers and/or cylinders have been bled.
- Carefully lower the vehicle.
- Check the brake pedal for "sponginess". If the condition is found, the entire bleeding procedure must be repeated.
- Remove tools J 35589 and J 29532.
- Refill the master cylinder to the proper level with brake fluid.
- DO NOT attempt to move the vehicle unless a firm brake pedal is obtained.