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

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

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 (0-1000kPa/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.

Wheel Brake Adjustment

The front wheel brakes are air operated. The rear wheel brakes are hydraulically operated.

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 initial adjustment procedure is the same for both types of wheel brakes.

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.

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 brakes in turn.

Front Wheel Brake 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 piston (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

1. Check the brake fluid level in the master cylinder reservoirs and top up if necessary. ENSURE THAT THE BRAKE FLUID LEVEL IS MAINTAINED THROUGHOUT THE ENTIRE BLEEDING PROCEDURE.

2. Park the machine and apply the parking brake. Ensure that the transmission is in neutral, start the engine and allow the compressor to charge the air system to governor cut-out pressure. Stop the engine.

3. Have an assistant fully depress the brake pedal and hold it down.

4. Open the bleed screw on each master cylinder in turn and leave open until the flow of brake fluid stops.

MASTER CYLINDER BLEED SCREW
Two Axle Machines

MASTER CYLINDER BLEED SCREW
Three Axle Machines (One each side)

5. Close the bleed screws and release the brake pedal.

6. Repeat steps 3, 4 and 5 until there is no evidence of air in the brake fluid.

NOTE: Observe the air pressure gauges in the cab. If the pressure falls to the bottom of the green zone restart the engine and allow the compressor to charge the system to governor cut-out. Stop the engine.

SLAVE CYLINDER BLEED SCREW

7. Have an assistant fully depress the brake pedal and hold it down.

8. Open the slave cylinder bleed screw and leave open until brake fluid flow stops.

9. Close the bleed screw and release the brake pedal.

10. Repeat steps 7, 8 and 9 until fluid flows free of air.

11. Repeat steps 7, 8, 9 and 10 for the other axle (Three axle machine).

NOTE: Bleed one wheel brake at a time and ensure that the pressure in the air reservoirs is maintained (gauges in the green zone) throughout the bleeding operation.

Master Cylinder Stroke

The stroke of the master cylinder can be checked as a means of assisting with the location of a problem. Too short a master cylinder stroke can indicate:

1. a seized or damaged master cylinder.

2. a seized or damaged slave cylinder.

3. low air pressure.

Too long a master cylinder stroke can be an indication of:

1. Low brake fluid level.

2. Air in the brake hydraulic circuit.

3. Leakage in the brake fluid lines.

4. Brake linings out of adjustment or worn excessively.

5. Failure of the master cylinder piston seal.

Too long a master cylinder stroke should be accompanied by a flashing light in the cab.

To check the master cylinder stroke use Caterpillar Displacement Gauge FT1097 and a 6.4 mm (0.25in.) diameter by 305 mm (12in.) long rod.

1. Remove the breather fitting (1) on the air/hydraulic actuator and install an FT1097 displacement gauge. Use a 6.4 mm (0.25in.) diameter by 305 mm (12in.) long rod in place of the rod provided with the gauge.

AIR/HYDRAULIC ACTUATOR

2. Ensure that the air system is fully charged and with the brake pedal released push the gauge down until it comes into contact with the air cylinder piston. Measure the length of the rod.

3. Fully depress the brake pedal and push the displacement gauge rod down again until it contacts the air cylinder piston. Measure the length of the rod.

4. The difference between the lengths is the stroke of the master cylinder.

The master cylinder stroke should be at least 58.6 mm. If it is less than that a fault such as a damaged master cylinder or slave cylinder is indicated.

The maximum master cylinder stroke is 187.4 mm. If the stroke is at its maximum the warning light in the cab should flash. If not locate the cause of the excessive stroke first and then check out the operation of the warning circuit.

Parking Brake Adjustment

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