Antilock Brake System Bleeding Procedures
BLEEDING BENDIX ANTILOCK 4 BRAKE SYSTEM
The base brakes and Antilock Brake System must be bled anytime air is permitted to enter the hydraulic system, due to disconnection of brake lines, hoses or components.
If the Antilock Modulator Assembly is removed from the vehicle, both the Base Brake System and the Antilock Brake System must be bled using the appropriate procedure. It is important to note that excessive air in the brake system will cause a soft or spongy feeling brake pedal.
During brake bleeding operations, ensure that brake fluid level remains close to the FULL level in the reservoir. Check brake fluid level periodically during bleeding procedure, adding DOT 3 brake fluid as required.
CAUTION: The base brake and Antilock brake hydraulic systems, on the Bendix Antilock 4 Brake System, can NOT be bled using any type of brake pressure bleeding equipment. This type of bleeding equipment does not develop the pressure required in the brake hydraulic system, to adequately bleed all trapped air. The only method which should be used for bleeding the base brakes hydraulic system, on a vehicle equipped with the Bendix Antilock 4 Brake System. Is the manual procedure of pressurizing hydraulic system, using constant moderate to heavy foot pressure on brake pedal.
The Antilock portion of brake system MUST be bled using the DRB Scan Tool and the bleeding sequence procedure outlined below.
BENDIX ANTILOCK 4 MODULATOR ASSEMBLY BLEEDING PROCEDURE
1. Assemble and install all brake system components on the vehicle, making sure all hydraulic fluid lines are installed and properly torqued.
2. Bleed the base brake system, using ONLY the bleeding procedure outlined in Service Adjustments.
To perform the bleeding procedure on the ABS modulator assembly, the battery, battery tray, battery tray support bracket and acid shield must be removed from vehicle. Then reconnect the vehicle's battery to vehicle's battery cables, using ONLY approved battery jumper cables.
3. Connect the DRB Scan Tool to the vehicle's diagnostic connector. The vehicle diagnostic connector is located behind the fuse panel access cover on the lower section of the dash panel left of the steering column. The diagnostic connector for the 1995 model year has been changed. It is now a black 8 way connector but is compatible to the DRB Scan Tool 6 way connector.
4. Using the DRB Scan Tool check to make sure the CAB does not have any stored fault codes, if it does, remove them using the DRB Scan Tool.
WARNING: WHEN BLEEDING THE MODULATOR ASSEMBLY WEAR SAFETY GLASSES. A CLEAR BLEED TUBE MUST BE ATTACHED TO THE MODULATOR BLEED SCREWS AND SUBMERGED IN A CLEAR CONTAINER FILLED PART WAY WITH FRESH CLEAN BRAKE FLUID. DIRECT THE FLOW OF BRAKE FLUID AWAY FROM THE PAINTED SURFACES OF THE VEHICLE. BRAKE FLUID AT HIGH PRESSURE MAY COME OUT OF THE BLEEDER SCREWS, WHEN OPENED.
When bleeding Antilock modulator assembly, the following bleeding sequence MUST be followed to insure a complete bleeding of all air from the Antilock brake, and base brake hydraulic systems. The modulator assembly can ONLY be bled using a manual bleeding procedure to pressurize the hydraulic system.
MODULATOR ASSEMBLY CIRCUIT BLEEDING PROCEDURE AND SEQUENCE
Fig. 1 BLEEDING MODULATOR ASSEMBLY PRIMARY CHECK VALVE CIRCUIT:
1 MODULATOR PRIMARY CHECK VALVE CIRCUIT
Note: To bleed hydraulic circuits of the Bendix Antilock 4 Brake System modulator assembly, the aid of a second mechanic or helper will be required to pump the brake pedal.
1. Install a clear bleed tube (such as Tygon) on primary check valve circuit bleed screw (Fig. 1). Then install bleed tube into a clear container partially filled with fresh clean brake fluid (Fig. 1).
2. Pump brake pedal several times, then apply and hold a constant medium to heavy force on brake pedal.
3. Open primary check valve circuit bleed screw (Fig. 1) at least 1 full turn to ensure an adequate flow of brake fluid. Continue bleeding primary check valve circuit until brake pedal bottoms.
4. After brake pedal bottoms, close and tighten bleed screw. Then release brake pedal. Do not release brake pedal prior to closing and tightening bleed screw.
5. Continue bleeding modulator assembly, repeating steps 2 through 4 until a clear, bubble free flow of brake fluid is evident.
6. When all air is bled from primary check valve circuit, tighten bleed screw and remove bleed hose from bleed screw. Do not remove bleed hose before tightening bleed screw, air may re-enter modulator.
7. Torque modulator assembly primary bleed screw to 9 Nm (80 in. lbs.).
Fig. 2 BLEEDING MODULATOR ASSEMBLY SECONDARY CHECK VALVE CIRCUIT:
2 MODULATOR SECONDARY CHECK VALVE CIRCUIT
1. Move clear bleed tube to secondary check valve circuit bleed screw (Fig. 2). Then install bleed tube into a container partially filled with fresh clean brake fluid (Fig. 2).
2. Pump brake pedal several times, then apply and hold a constant medium to heavy force on brake pedal.
3. Open secondary check valve circuit bleeder screw (Fig. 2), at least 1 full turn to ensure an adequate flow of brake fluid. Continue to bleed secondary check valve circuit until the brake pedal bottoms.
4. After brake pedal bottoms, close and tighten bleed screw and release brake pedal. Do not release brake pedal prior to closing and tightening bleed screw.
5. Continue bleeding secondary check valve circuit, repeating steps 2 through 4, until a clear, bubble free flow of brake fluid is evident.
6. When air is bled from primary check valve circuit, tighten bleed screw and remove bleed hose from bleed screw. Do not remove bleed hose before tightening bleed screw, air may re-enter modulator.
7. Torque modulator assembly primary bleed screw to 9 Nm (80 in. lbs.).
Fig. 3 BLEEDING MODULATOR ASSEMBLY PRIMARY SUMP CIRCUIT:
3 MODULATOR ASSEMBLY PRIMARY SUMP CIRCUIT
1. Move clear bleed tube to primary sump bleed screw (Fig. 3). Then install bleed tube into a container partially filled with fresh clean brake fluid (Fig. 3).
2. Pump brake pedal several times, then apply and hold a constant medium to heavy force on brake pedal.
3. Open modulator assembly primary sump circuit bleed screw (Fig. 3) at least 1 full turn. This will ensure an adequate flow of brake fluid from the primary sump circuit.
4. Using the DRB Scan Tool, select the bleed ABS hydraulic unit mode, and then select the primary circuit. (The RF and LR solenoids will alternately fire for five seconds). Using the DRB Scan Tool, continue to select the primary circuit until an air-free flow of brake fluid from primary sump bleed screw is maintained or brake pedal bottoms. If an air-free flow is not maintained before brake pedal bottoms, close bleed screw and repeat steps 2 to 4, until an air free flow is maintained.
5. After an air-free flow of brake fluid is maintained from primary sump bleed screw, close and lightly tighten bleeder screw. Then release brake pedal. Do not release brake pedal prior to closing and tightening bleeder screw.
6. After primary sump bleed screw is closed, remove bleed hose from primary sump bleed screw.
7. Torque modulator assembly primary sump bleed screw to 9 Nm (18 in. lbs.).
Fig. 4 BLEEDING MODULATOR ASSEMBLY PRIMARY ACCUMULATOR CIRCUIT:
4 MODULATOR ASSEMBLY PRIMARY ACCUMULATOR CIRCUIT
8. Transfer clear bleed tube to primary accumulator bleed screw (Fig. 4). Then install bleed tube into a container partially filled with fresh clean brake fluid (Fig. 4).
9. Pump brake pedal several times, then apply a constant medium to heavy force on the brake pedal. Using the DRB Scan Tool, select the bleed ABS hydraulic unit mode, and then select the primary circuit valves. (The RF and LR modulator assembly solenoids will tire for 5 seconds).
10. Open the modulator assembly primary accumulator circuit bleed screw (Fig. 4) at least one lull turn. This will ensure an adequate flow of brake fluid from the primary accumulator circuit. Continue bleeding primary accumulator circuit until an air-free flow of brake fluid from bleed screw is maintained or the brake pedal bottoms. If an air-free flew of brake fluid is not maintained before brake pedal bottoms, close bleed screw and repeat steps 8 and 9 until an air free flow is maintained.
11. After an air-free flow of brake fluid is maintained from the primary accumulator bleed screw, close and lightly tighten bleed screw. Then release pressure from brake pedal. Do not release force from brake pedal prior to closing and tightening bleed screw.
Note: For the next modulator assembly bleeding procedure, use of the DRB Scan Tool is not required. This step of the bleed procedure does not require modulator solenoids to be operated for bleeding to be performed.
12. Pump brake pedal several times, then apply and hold a constant medium to heavy force on the brake pedal.
13. Again without firing modulator solenoids, open primary accumulator circuit bleed screw (Fig. 4) 1 full turn. This will ensure an adequate flow of brake fluid from the primary accumulator circuit.
14. Bleed primary accumulator circuit until a clear, air-free flow of brake fluid is maintained from the accumulator bleed screw or the brake pedal bottoms. If an air-free flow of brake fluid is not maintained from the bleed screw before the brake pedal bottoms. First, close bleed screw and then repeat steps 11 and 12 of this bleeding procedure until an air-free flow is maintained.
15. After an air-free flow of brake fluid is maintained from the primary accumulator circuit bleed screw, close and lightly tighten bleed screw. Then release force from brake pedal. Do not release force from brake pedal prior to closing and tightening bleeder screw.
16. After primary accumulator bleed screw is closed, remove bleed hose from bleed screw.
17. Torque primary accumulator bleed screw to 9 Nm (80 in. lbs.).
Fig. 5 BLEEDING MODULATOR ASSEMBLY SECONDARY SUMP CIRCUIT:
5 MODULATOR ASSEMBLY SECONDARY SUMP CIRCUIT
1. Transfer clear bleed tube to secondary sump bleed screw on modulator assembly (Fig. 5). Then install bleed tube into a container partially filled with fresh clean brake fluid (Fig. 5)
2. Pump brake pedal several times, then apply and hold a constant medium to heavy force on brake pedal.
3. Open the secondary sump circuit bleed screw (Fig. 5) at least 1 lull turn. This will ensure an adequate flow of brake fluid is expelled from the secondary sump circuit.
4. Using the DRB Scan Tool, select the bleed ABS hydraulic unit mode, and then select the secondary circuit valves. (The LF and RR solenoids will alternately fire for five seconds). Continue bleeding Secondary sump circuit until an air-free flow of brake fluid from secondary sump bleed screw is maintained or brake pedal bottoms. If an air-free flow of brake fluid is not maintained before brake pedal bottoms, close bleed screw and repeat steps 2 through 4 until an air-free flow is maintained.
5. After an air-free flow of brake fluid is maintained from secondary sump bleed screw, close and lightly tighten bleed screw. Then release force from brake pedal. Do not release brake pedal prior to closing and tightening bleeder screw.
6. After secondary sump bleed screw is closed, remove bleed hose from bleed screw.
7. Torque secondary sump bleed screw to 9 Nm (80 in. lbs.).
Fig. 6 BLEEDING MODULATOR ASSEMBLY SECONDARY ACCUMULATOR CIRCUIT:
6 MODULATOR ASSEMBLY SECONDARY ACCUMULATOR CIRCUIT
8. Transfer bleed tube to secondary accumulator bleed screw (Fig. 6). Then install bleed tube into a container partially filled with fresh clean brake fluid (Fig. 6).
9. Apply constant, medium to heavy force on brake pedal. Then using the DRB Scan Tool, select the bleed ABS hydraulic unit mode, and then select the secondary circuit valves. (The LF and RR modulator assembly solenoids will fire for 5 seconds).
10. Open the secondary accumulator circuit bleed screw (Fig. 6) at least one full turn. This will ensure an adequate flow of brake fluid is expelled from the secondary accumulator circuit. Continue to bleed primary accumulator circuit, until an air-free flow of brake fluid from the bleed screw is maintained or brake pedal bottoms. If an air-free flow of brake fluid is not maintained from bleed screw before brake pedal bottoms, close bleed screw and then repeat steps 8 and 9 until an air free flow is maintained.
11. After an air-free flow of brake fluid is maintained from the bleed screw, close and lightly tighten the bleed screw. Then release force from brake pedal.
Do not release force from brake pedal prior to closing and tightening bleeder screw.
Note: For the next modulator assembly bleeding procedure, use of the DRB Scan Tool is not required. This step of the bleeding procedure does not require the modulator solenoids to be operated for bleeding to be performed.
12. Pump brake pedal several times, then apply and hold constant medium to heavy force on brake pedal.
18. Again without firing modulator assembly solenoids, open secondary accumulator circuit bleed screw (Fig. 6) at least 1 full turn. This will ensure an adequate flow of brake fluid is expelled from the secondary accumulator circuit.
14. Bleed secondary accumulator circuit until a clear, air-free flow of brake fluid is maintained from the secondary accumulator bleed screw or the brake pedal bottoms. If an air-free flow of brake fluid is not maintained from secondary accumulator bleed screw before brake pedal bottoms. Repeat steps 12 and 13 of this bleeding procedure until an air-free flow is maintained from the bleeder screw.
15. Alter an air free flow of brake fluid is maintained from secondary accumulator circuit bleed screw, close and lightly tighten bleed screw. Then release force from brake pedal. Do not release force from brake pedal prior to closing and tightening bleed screw.
16. Alter secondary accumulator bleed screw is closed, remove bleed hose from bleed screw.
17. Torque secondary accumulator bleed screw to 9 Nm 80 in. lbs.).