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 downstream 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. It must be bled out. 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 (and the brake pressure modulator valve or combination valve on ABS systems) 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 for 1982-91 vehicles is:
The correct bleeding sequence for 1992-94 vehicles is:
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 and 2
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.
In addition to a length of clear neoprene bleeder hose, bleeder wrenches and a clear bleeder bottle (old plastic jar or drink bottle will suffice), bleeding late-model ABS systems may also require the use of one or more relatively inexpensive combination valve pressure bleeding tools (which are used to depress one or more valves in order to allow component/system bleeding). To fully bleed the late model ABS systems, a scan tool should also be used to run the system through functional tests.
- 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. To prevent squirting fluid, and possibly damaging painted surfaces, install the cover during the procedure, but be sure to frequently check and top off the reservoirs with fresh 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 at the master cylinder and allow the fluid to flow from the front port.
- Have a friend depress the brake pedal slowly and hold (air and/or fluid should be expelled from the loose fitting). Tighten the line, then release the brake pedal and wait 15 seconds. Loosen the fitting and repeat until all air is removed from the master cylinder bore.
- When finished, tighten the line fitting to 20 ft. lbs. (27 Nm).
- Repeat the sequence at the master cylinder rear pipe fitting.
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 opened. Otherwise, air will be drawn back into the system.
- Check and refill the master cylinder reservoir.
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.
- On late model ABS equipped vehicles, perform the special ABS procedures as described later in this section. On 4 wheel ABS systems the Brake Pressure Modulator Valve (BPMV) must be bled (if it has been replaced or if it is suspected to contain air) and on most Rear Wheel Anti-Lock (RWAL) systems the combination valve must be held open. In both cases, special combination valve depressor tools should be used during bleeding and a scan tool must be used for ABS function tests.
- 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.
The proper sequence for 1982-91 vehicles is:
- Right rear
- Left front
- Left rear
- Right front
The proper sequence for 1992-94 vehicles is:
- 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.
Be very careful when bleeding wheel cylinders and brake calipers. The bleeder screws often rust in position and may easily break off if forced. Installing a new bleeder screw will often require removal of the component and may include overhaul or replacement of the wheel cylinder/caliper. To help prevent the possibility of breaking a bleeder screw, spray it with some penetrating oil before attempting to loosen it.
- Submerge the other end of the tube in a transparent container of clean brake fluid.
- Loosen the bleed screw, then have a friend apply the brake pedal slowly and hold. Tighten the bleed screw to 62 inch lbs. (7 Nm), release the brake pedal and wait 15 seconds. Repeat the sequence (including the 15 second pause) until all air is expelled from the caliper or cylinder.
- Tighten the bleeder screw to 62 inch lbs. (7 Nm) when finished.
- 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.
- After bleeding, make sure that a firm pedal is achieved before attempting to move the vehicle.
See Figure 3
For the lucky ones with 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 hydraulic 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 for 1982-91 vehicles:
The following sequence should be used for 1992-94 vehicles:
- 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.