797F Off-Highway Truck: Brake and Hoist System Troubleshooting

Check: Check the screens for the hoist and for the brake cooling.

Steep retarding arrangement (1) Screens for the hoist and for the brake cooling (2) Bypass switches(3) Gear pump for the hoist and for the brake cooling

Remove screens (1) for the hoist and for the brake cooling. Inspect screens (1) for foreign material or for restrictions.

Note: Screens (1) for the hoist and for the brake cooling have an oil bypass valve. The bypass valve allows the oil to bypass the oil filter element or the screen whenever the pressure difference between the inlet oil and the outlet oil becomes too high. Any oil that does not flow through the filter element or through the screen goes directly into the hydraulic circuit. Dirty oil can cause sticking valves and restrictions in valve orifices. Bypass switches (2) will notify the operator of a restriction.

Problem: Rubber particles are found.

Probable Cause

• Seal failure
• Hose failure

Problem: Shiny steel particles are found.

Probable Cause

Shallow retarding arrangement(3) Gear pump for the hoist and for the brake cooling

• Mechanical failure of gear pump (3) for the hoist and for the brake cooling

Problem: The gear pump for the hoist and for the brake cooling makes noise and the cylinder rods do not move evenly. Also, there are air bubbles in the oil.

Shallow retarding arrangement(3) Gear pump for the hoist and for the brake cooling

(4) Hoist relief valve (5) Control valve for the hoist and for the brake cooling (6) Hoist control valve (7) Relief valve for the rod end of the hoist cylinders(8) Relief valve for the head end of the hoist cylinders

Probable Cause

• Hoist relief valves (4) open at low oil pressure.
• Relief valve (8) for the head end of the hoist cylinders opens at low oil pressure.
• There is a loose connection in one or more oil lines on the inlet side of gear pump (3) .
• Gear pump (3) for the hoist and for the brake cooling is worn.

Problem : The temperature of the oil is too hot.

Probable Causes

• The viscosity of the oil is incorrect.
• Hoist relief valves (4) open at low oil pressure.
• Relief valve (8) for the head end of the hoist cylinders opens at low oil pressure.
• Relief valve (7) for the rod end of the hoist cylinders opens at low oil pressure.
• One of the spools in hoist control valve (6) is jammed.
• One of the spools in control valve (5) for the hoist and for the brake cooling is jammed in the closed position.
• Gear pump (3) for the hoist and for the brake cooling is worn.
• There is a restriction in an oil passage.
• The load on the system is too high.
• There is a restriction in the lines or in the front or rear brake oil coolers.
• The slack adjuster is not completely releasing. This causes the brakes to be partially engaged.

Problem : The output of the gear pump for the hoist and for the brake cooling is too low.

Probable Cause

• The hydraulic tank oil level is too low.
• The viscosity of the oil is incorrect.
• Gear pump (3) for the hoist and for the brake cooling is worn.

Problem : The pressure of the oil in the head end of the hoist cylinders is too low.

• Hoist relief valves (4) open at low oil pressure.
• Relief valve (8) for the head end of the hoist cylinders opens at low oil pressure.
• One or both of the spools in control valve (5) for the hoist and for the brake cooling is jammed in the open position.
• The spool in hoist control valve (6) that opens the drain from the head end to the hydraulic tank is jammed in the open position.
• Both spools in hoist control valve (6) that control the oil that is flowing to the rod end of the hoist cylinders are jammed in the open position.
• The pressure setting of the pressure reducing valve in the chassis/brake valve is low.

Problem: The pressure of the oil in the rod end of the hoist cylinders is too low.

• Hoist relief valves (4) open at low oil pressure.
• Relief valve (7) for the rod end of the hoist cylinders opens at low oil pressure.
• One or both of the spools in control valve (5) for the hoist and for the brake cooling is jammed in the open position.
• The spool in hoist control valve (6) that opens the drain from the rod end to the hydraulic tank is jammed in the open position.
• Both spools in hoist control valve (6) that control the oil that is flowing to the head end of the hoist cylinders are jammed in the open position.
• The pressure setting of the pressure reducing valve in the chassis/brake valve is low.

Troubleshooting for Brake Oil Overheating

If an overheating condition in the hydraulic system occurs, the operator will probably become aware of the overheating condition through the Advisor.

(1) Brake oil temperature gauge(2) Display for the Advisor

The Advisor receives signals from temperature sensors. At each of the four brakes, there is a temperature sensor that senses the temperature of the oil. Brake oil temperature gauge (1) will display this sensor input.

(A) Temperature reading of 110°C (230°F)(B) Temperature reading of 124°C (255°F)

Check brake oil temperature gauge (1) regularly. During this test sequence, do not allow the temperature of the brake oil to get too hot. This can cause damage to the brakes.

When the oil temperature is too hot for the current conditions, Advisor (2) will alert the operator. An event will be displayed on the display for Advisor (2). If the brake oil is too hot, reduce the load on the machine or slow the machine speed. Also, downshift the transmission to a lower speed. For additional cooling, parking the truck in a convenient location. Put the transmission in NEUTRAL, and run the engine at approximately 1500 rpm.

Symptom/Fault Code: Service Brakes Dragging/Overheating

Table 17

Problem: Brake Cooling Temperature Too High (Above 120° C (248° F))
Possible Component Root Causes	Non-Component Root Causes	How to Diagnose	Corrective Action
Unloader System Failure	Unloader tank spikes Back pressure from high pump command fault	Refer to Table 12 in the "Symptom/Fault Code: High Brake Pump Command" Section.	Refer to Table 12 in the "Symptom/Fault Code: High Brake Pump Command" Section.
Diverter Valve (Front Service Brake)	Contamination	Check brake system pressure to ensure that pressure upstream of the slack adjustor drops to 0 kPa (0 psi) in less than 1 second with normal operating conditions. If the pressure takes more than 1 second to decay then the valves may not be shifting properly.	Service with new kit for the diverter valve (service brakes). Make sure that oil is ISO 18/15 or better.
Diverter Valve (Rear Service Brake)	Contamination	Check brake system pressure to ensure that pressure upstream of the slack adjustor drops to 0 kPa (0 psi) less than 1 second with normal operating conditions. If the pressure takes more than 1 second to decay, then the valves may not be shifting properly.	Service with new kit for the diverter valve (service brakes). Make sure that oil is ISO 18/15 or better.
Solenoid valve (Front Automatic Retarder Control)	Contamination Minimum current set too high	Check brake system pressure to ensure that pressure upstream of the slack adjustor drops to 0 kPa (0 psi) in less than 1 second with normal operating conditions. If the pressure takes more than 1 second to decay, then the valves may not be shifting properly.	Service with new ARC solenoid valve. Make sure that oil is ISO 18/15 or better.
Solenoid valve (Rear Automatic Retarder Control)	Contamination Minimum current set too high	Check brake system pressure to ensure that pressure upstream of the slack adjustor drops to 0 kPa (0 psi) in less than 1 second with normal operating conditions. If the pressure takes more than 1 second to decay then the valves may not be shifting properly.	Service with new ARC solenoid valve. Make sure that oil is ISO 18/15 or better.
Slack Adjustor	N/A	Perform residual pressure check. If the residual pressure is higher than specification, then there may be a problem with the slack adjustor.	Service Slack adjustor. Make sure that oil is ISO 18/15 or better.
Brake Pedal Valve	Contamination Debris under heal stop of pedal.	Check brake system pressure to ensure that pressure upstream of the slack adjustor drops to 0 kPa (0 psi) in less than 1 second with normal operating conditions. If the pressure takes more than 1 second to decay then the valves may not be shifting properly.	Ensure then pedal is clean and free of debris. Service with New Pedal Valve. Make sure that oil is ISO 18/15 or better.

Symptom/Fault Code: Parking Brakes Dragging/Overheating

Table 18

Problem: Brake Cooling Temperature Too High (Above 120° C (248° F))
Possible Component Root Causes	Non-Component Root Causes	How to Diagnose	Corrective Action
Unloader System Failure	Unloader tank spikes and/or back pressure from high pump command fault	Refer to Table 12 in the "Symptom/Fault Code: High Brake Pump Command" Section	Refer to Table 12 in the "Symptom/Fault Code: High Brake Pump Command" Section
TCS On/Off Valve	Contamination	Check to see if the AETA self test is working properly. Ensure that the left and right rear parking brake pressure increases and decreases smoothly. If one side does not cycle, then inspect and repair the AETA valve.	Service with New AETA valve. Make sure that oil is ISO 18/15 or better.
TCS Proportional Valve	Contamination Set too low	Check to see if the AETA self test is working properly. Ensure that the left and right rear parking brake pressure increases and decreases smoothly. If one side does not cycle, then inspect and repair the AETA valve.	Service with new AETA valve. Make sure that oil is ISO 18/15 or better.
Diverter Valve for the Parking and Secondary Brake	Contamination	Check brake system pressure to ensure that pressure at the brake pack drops to 0 kPa (0 psi) in less than 1 second with normal operating conditions. If the pressure takes more than 1 second to decay, then the valves may not be shifting properly.	Service with new diverter valve for the parking and secondary brake. Make sure that oil is ISO 18/15 or better.
Solenoid Valve for the Parking and Secondary Brake	Contamination	Check brake system pressure to ensure that pressure at the brake pack drops to 0 kPa (0 psi) in less than 1 second with normal operating conditions. If the pressure takes more than 1 second to decay, then the valves may not be shifting properly.	Service with new solenoid valve for the parking and secondary brake. Make sure that oil is ISO 18/15 or better.
Brake Pack	Glycol in the oil Tolerance Stack up incorrect	Check to see if the tolerance/stack up is OK. Check to see if the coolers are leaking, or if the coolant is low.	Perform manual brake wear check. Check for glycol in the oil sample.
Left and Right Pressure Sensors for the Traction Control System Valve	N/A	With machine off, verify that the sensors are not reading any pressure. With Parking Brake released, the TCS valve pressure on the sensors and the TCS valve pressure on the gauges should match.	Replace pressure sensors for the TCS valve

Problem: The oil temperature is hot.

The oil temperature is too hot according to brake oil temperature gauge (1). Advisor (2) is alerting the operator of high brake oil temperature.

Probable Cause

The truck is being operated improperly.

ReferenceSee the Operation and Maintenance Manual for the correct operating techniques of the brake and retarder system.

Operate the machine again. Make sure that engine rpm does not drop below 1700 rpm. This ensures that enough oil flows through the brake oil coolers in order to keep the oil at normal operating temperature.

Problem: The oil temperature is hot on a properly operated machine.

The oil temperature is too hot according to brake oil temperature gauge (1) and Advisor (2) after the truck is operated correctly. Advisor (2) can display an event about the brake oil temperature.

Probable Cause

• There is a restriction in the oil cooling system. Refer to the Braking System Testing and Adjusting, "Brake Cooling Pressure - Check". Also, use a flow meter in order to determine if there is proper brake cooling oil flow.
• One of the following pumps has failed: The gear pump for the hoist and for the brake cooling, the piston motor that drives the brake cooling pump, or the brake cooling pump. Refer to this publication in order to check the appropriate filters or screens.
• The pressure setting of the rear brake oil cooler relief valve is too low. Refer to the Braking System Testing and Adjusting, "Relief Valve (Brake Oil Cooler) - Test and Adjust".
• The pressure setting of the front brake oil cooler relief valve is too low. Refer to the Braking System Testing and Adjusting, "Relief Valve (Brake Oil Cooler) - Test and Adjust".
• Brake drag that can be caused by high command of the brake pump.

MARYGAR

797F Off-Highway Truck: Brake and Hoist System Troubleshooting 2012-12-01T15:57:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown