Testing And Adjusting

Usage:

Troubleshooting

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When working with compressed air wear safety glasses and protective clothing.

PROBLEM:

Low air pressure.

POSSIBLE CAUSES:

1. Broken spring on compressor inlet valve.

2. Compressor unloader plungers sticking, thus holding inlet valves off their seats.

3. Governor set too low.

4. Air dryer check valve leaking.

5. Safety valve leaking or blowing off too early.

6. Reservoir drain tap leaking.

7. Leaking hoses/valves/actuators.

PROBLEM:

High air pressure (safety valve may blow off).

POSSIBLE CAUSES:

1. Governor set too high.

2. Compressor cut-out mechanism faulty.

PROBLEM:

Inter-axle differential lock clutch fails to disengage.

POSSIBLE CAUSES:

1. Actuating cylinder damaged.

2. Low air pressure.

PROBLEM:

Inter-axle differential lock clutch fails to engage.

POSSIBLE CAUSES:

1. Differential lock valve leaking air to the actuating cylinder.

2. Actuator cylinder damaged.

PROBLEM:

Brake failure (service brake).

POSSIBLE CAUSES:

1. Diaphragm in service chamber of spring brake actuator ruptured.

2. Dual brake valve fault.

3. Quick release valve not passing air.

4. Air in hydraulic fluid.

5. Worn brake linings.

6. Brake master cylinder jammed.

7. Double check valve stuck in mid-position blocking the outlet port

PROBLEM:

Brake failure (parking brake).

POSSIBLE CAUSES:

1. Relay valve failing to exhaust air either directly from the spring chamber of the brake actuators (front axle) or from the park brake actuator.

2. Actuator power spring broken.

3. Actuator piston sticking.

4. Relay valve stuck closed.

5. Pilot pressure holding relay valve open due to faulty parking brake valve.

PROBLEM:

Service/Parking brakes inefficient.

POSSIBLE CAUSES:

1. Brake linings worn.

2. Brakes out of adjustment (automatic adjusters may be damaged or seized).

3. Air in brake hydraulic system.

4. Leakage from hoses, tubes, fittings or seals.

5. Low brake fluid level.

PROBLEM:

Hot or dragging brakes.

POSSIBLE CAUSES:

1. Air in brake hydraulic system.

2. Brake seized on.

PROBLEM:

Suspension self levelling continues when the service brakes are applied and/or when the park brake is applied.

POSSIBLE CAUSE:

1. Sticking spool valve(s) in air line to rotary valve.

Governor

The governor cut-out pressure can be adjusted if necessary:-

1. Install an accurate pressure gauge (0-1000 kPa/0-150 p.s.i.) in test port (4).

2. Start the engine and allow the system to charge up to governor cut-out pressure. The compressor has cut-out when the reading on the pressure gauge stops rising.

3. If necessary, adjust the cut-out pressure by slackening the locknut (3) and turning adjusting screw (2). Turn counter-clockwise to increase the cut-out pressure. The correct value is given in "specifications". After turning the screw clockwise (to reduce the cut-out pressure) it will be necessary to exhaust air from the system until the compressor cuts in and re-charges the system to the new cut-out pressure.

Ensure that the adjusting screw is locked in place and replace the rubber cover (1).

GOVERNOR

GOVERNOR
1. Rubber Cover 2. Adjusting Screw 3. Locknut 4. Test Port.

4. With the system charged to the correct cut-out pressure slowly lower the pressure until the compressor cuts in and note the reading. The compressor has cut-in when the pressure reading on the gauge starts to rise again.

5. If the cut-out/cut-in pressure readings are not within the values given in "specifications" after adjustment the governor must be disassembled and overhauled or replaced.

System Protection Valve

Pressure Setting

1. Install an accurate pressure gauge (0-1000 kPa/0-150 p.s.i.) in the governor test port.

2. Remove the outlet pipe from any one element in the system protection valve.

SYSTEM PROTECTION VALVE

3. Start the engine and operate at low idle.

4. Note the reading on the pressure gauge when air begins to flow from the disconnected port.

5. If the setting is incorrect, stop the engine, remove the rubber gaiter from the relevant element and turn the adjusting screw to vary the setting. Turn clockwise to increase the setting.

6. Exhaust pressure from the air dryer (crack the inlet pipe), restart the engine, repeat the test until the setting is correct.

7. Repeat steps 2 to 6 for each element in turn.

8. Remove the test gauge and replace and tighten all fittings.

Front Wheel Brake Adjustment

The wheel brakes are self adjusting during normal operation and should maintain the correct clearances between the linings and drums until the linings are replaced. An initial adjustment is required when the linings are replaced or if the brake assembly has been disassembled for any reason.

The brake linings should be checked for wear every 250 service meter hours and replaced when they are worn to 8 mm thickness.

Initial Adjustment

1. Remove both dust covers from the wheel brake.

BRAKE LININGS

2. Turn the adjusting screw (1) until the brake lining is in contact with the drum (2). DO NOT FORCE THE ADJUSTING SCREW.

ADJUSTING SCREW

3. Turn the adjusting screw (1) in the opposite direction until the clearance between the lining and drum (measured at the centre of the lining) is 2mm maximum. This should take about eight notches or clicks of the adjuster.

4. Repeat steps 2 and 3 using the other adjusting screw to set the clearance between the other brake lining and drum.

5. Install the dust covers.

6. Repeat the entire procedure for the other wheel brake.

Front Axle Cylinder Adjustment

If the brake cylinder assembly has been replaced for any reason it will be necessary to carry out the following adjustment to ensure correct installation. Carry out the procedure before installing the brake actuator.

1. Check the position of the wedge assembly (2) to be sure the rollers (10) are correctly positioned against the plunger assemblies (1).

2. Apply 9S3263 threadlock to the threads of the tube (8) - countersunk end, and screw the tube fully into the brake cylinder assembly (9).

3. Install the follower assembly (3).

4. Connect the air lines to the brake actuator (6).

5. Start the engine and allow the system pressure to increase to normal. Move the parking brake control valve lever to the "OFF" position to fully retract the actuator pushrod (5). Place the actuator in position against the end of tube (8) so that pushrod (5) fits into follower (3).

CYLINDER ASSEMBLY

6. Measure the clearance (A) between the face of the actuator and the end of the tube.

TUBE ASSEMBLY

7. Remove the actuator (6).

8. Apply 9S3263 threadlock to the threads of the tube (8) and screw flange (4) on until the flange face is clear of the tube end by the clearance (A) measured in step 6. The mounting holes in the flange must be vertical. Back off the flange as required (up to one full turn) to obtain the vertical alignment.

9. Lock the flange (4) in position using set screw (7).

10. Install the brake actuator.

Bleeding The Rear Brakes

BLEED VALVE

Air in the brake hydraulic system may cause the brake to drag. To bleed the brakes:

1. Park the truck and apply the parking brake.

2. Run the engine until the air system is fully charged and shut down the engine.

3. With the service brake released open the bleed valve and allow air and fluid to flow. Close the bleed valve when all flow stops.

4. Top up the fluid reservoirs if necessary.

ENSURE THAT THE CORRECT FLUID IS USED AND THAT THE FLUID LEVEL IS MAINTAINED THROUGHOUT THE ENTIRE BLEEDING PROCEDURE.

BRAKE RESERVOIR

NOTE: The fluid level should be maintained at approximately 20mm below the top of the reservoir.

5. Apply the brake three times allowing at least thirty seconds between applications.

6. Repeat steps 3-5 until fluid flows free of air.

If the fluid reservoirs have become completely dry bleed the system as follows:-

1. Carry out steps 1, 2 and 4 above. Ensure that the reservoirs remain full.

2. Hold the brake pedal down and open the bleed valve to vent air from the master cylinder. When fluid flow stops, close the bleed valve and release the brake pedal. Wait for a minimum of two minutes and repeat.

3. With the bleed valve closed press the brake pedal fully down, hold for ten seconds and release. Wait for two minutes and repeat.

4. Repeat steps 2 and 3 as often as necessary to ensure that all air has been vented from the system. Always wait two minutes between brake applications to allow air to come to the top of the system.

5. After both rear wheel brakes have been bled in this way operate the truck for one hour and open each bleed valve (with the service brake released) to ensure the systems are completely vented.

Rear Brake Inspection

REAR WHEEL BRAKE
1. Frame Bolts 2. Retractor Springs.

1. Inspect the brakes to make sure that the frame bolts (1) are not loose and that the retractor springs (2) are not broken.

2. Look through the split (3) between the two halves of the brake frame to locate the lining (4) and steel shoe (5).

REAR WHEEL BRAKE
3. Split 4. Lining 5. Steel Shoe 6. Line.

3. Scribe a line (6) on the frame 19mm (0.750in) from the outside edge.

4. Have the brakes applied and compare the position of the steel shoe with the scribed line. If the top of the shoe coincides with the line, travel is at a maximum and the brake must be re-lined. It is recommended that the expander tube and shield assemblies are replaced when the brakes are relined.

Parking Brake Adjustment - (Machines with Parking Brake Mounted on Rear Frame)

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Before attempting to adjust the park brake ensure that the machine is parked on level ground with ALL wheels properly chocked.

Routine Adjustment of the park brake assembly is essential to ensure efficient operation.

1. Start the engine, allow the air system to charge and shut down the engine.

2. Release the park brake.

3. Remove dust cover (1).

PARK BRAKE

4. Measure the clearance between the brake shoes (2) and drum (3). The clearance should be 0,25±0,12mm.

PARK BRAKE - COVER REMOVED

5. If the clearance is incorrect turn the starwheel adjuster (4) until the correct clearance is obtained.

6. Install dust cover (1)

7. Apply the park brake.

Initial Adjustment

If the park brake assembly has been disassembled for any reason it will be necessary to set up the brake as follows:

1. Before installing the park brake actuator (7) onto the mounting bracket (6), use the starwheel adjuster to obtain the correct clearance between the brake shoe linings and the brake drum.

PARKING BRAKE ACTUATOR

2. Check the length of the park brake actuator pushrod assembly. Measure the distance (dimension 'X') between the face of the actuator and the centre line of the pin hole in the rod end (3). This should be 147±3mm. If the dimension is incorrect slacken jam nut (4) and turn rod end (3) up or down along pushrod (5) until the correct dimension is obtained. Tighten the jam nut (4).

3. Connect the air supply line to the actuator. Pressurise the actuator by moving the park brake valve to "OFF". The pushrod will move into the actuator. Measure the length of the pushrod. This should be 112±3mm (dimension 'Y').

4. If necessary repeat steps 2 and 3 to obtain correct dimensions.

NOTE: Check the position of the rod end. When the actuator is installed the lever (1) must fit into the slot in the rod end. Turn the rod end only far enough to align with the lever. Tighten the jam nut.

5. Install the park brake actuator onto the mounting bracket (6). Pull lever (1) down manually to take up all free movement in the linkage. Insert pin (2) through rod end (3) and lever (1).

6. Install the cotter pin in the end of pin (2). Check the tighteness of all fittings and the air supply connection.

Parking Brake Adjustment - (Machines with Transmission Mounted Parking Brake)

During normal operation the park brake requires no attention other than a periodic check to ensure it is not excessively worn. As the brake wears the stroke of the actuator rod increases. When the brake is fully worn the pin (5), will be fully visible through hole (4). The end of the pin is painted red. Check every 250 hours to ensure the brake does not need servicing.

PARK BRAKE INSPECTION HOLE

After using the brake to make an emergency stop it must be disassembled and all parts inspected. Inspect the plates and discs for distortion or severe discolouring and install new parts as required. Remove oil seal holder (6) and install a new oil seal (8) and O-ring seal (7).

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Do not neglect to install new seals. The heat generated during an emergency stop can damage the existing seals and cause leakage. This could impair the future efficiency of the unit.

When installing new parts it will be necessary to ensure the assembly is correctly set up:

1. With air pressure applied to the chamber (park brake OFF) turn back the rubber cover (1) and loosen lock nut (2).

2. Turn yoke (3) until pin (5) can be inserted.

3. Install the pin and ensure the brake turns freely.

4. Insert cotter pin (9), tighten the locknut (2) and refit the rubber cover.

PARK BRAKE ASSEMBLY