Magnetic Switch Group Fails on Certain 773E, 770G, and 772G Off-Highway Trucks{1408, 7499} Caterpillar

Off-Highway Truck/Tractor:

770G (S/N: ECM1-UP)

772G (S/N: LTS1-UP)

773E (S/N: KEG1-UP; ASK1-UP)

Introduction

ReferenceOperation and Maintenance, SEBU8394, "773E Off-Highway Truck", "Use of Wheel Chocks"

ReferenceOperation and Maintenance, SEBU8718, "770G and 772G Off-Highway Truck", "Prepare the Machine for Maintenance"

The problem that is identified in the technical information bulletin that follows does not have a known permanent solution. Until a permanent solution is known, use the solution that is identified below.

Problem

Illustration 1	g03729969

Reports have been received from the field of failures of the 241-8368 Magnetic Switch Gp (1). The magnetic switch group is the main power relay. The magnetic switch group has failed for the following reasons.

• Improper tightening of the two 4F-2294 Jam Nuts (2)

• Improper routing of the cable (3) will cause lead (4) to rub through the insulation on the electrical terminal causing a short to the metal case.

Solution

Tighten the two jam nuts on the 241-8368 Magnetic Switch Gp to the proper specification.

Perform the following rework procedures on the machines.

Rework procedure for the 773E Off-Highway Trucks

1. Permit only one operator on the machine. Either keep other personnel away from the machine, or keep other personnel in the sight of the operator.

2. Move the machine to a smooth horizontal location. Move the machine away from any machines that are working and any personnel. The surface must be solid enough to support the weight of the machine and any tooling that is used to support the machine.

3. Install the body retaining pins for the truck body.

4. Move the transmission control to the NEUTRAL position.

5. Move the parking brake switch to the ON position in order to engage the parking brakes. Turn the engine start switch to the OFF position in order to stop the engine.

6. Turn the battery disconnect switch to the OFF position. Remove the key. Secure the lock on the cover plate.

7. Place chocks in front of the wheels and behind the wheels. Refer to Operation and Maintenance Manual, SEBU8394, "Use of Wheel Chocks" for more information.

8. When you cannot use wheel chocks, ensure that the machine is unable to roll. Turn the wheels into a suitable bank, or place the wheels in a suitable ditch.

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Illustration 2	g03729931

9. Go to the back of the cab on the machine. Remove cover (1) from the back of the cab. Save the cover.

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Illustration 3	g03729958

10. Identify the position of the main power relay (2) .

11. Ensure that the cable assembly (3) is routed away from the metal case. Ensure that the relay case eliminates the possibility of a direct short.

12. Ensure that the other end of the cable assembly (3) is properly connected to the 171-2212 Circuit Breaker As without contacting other cables.

13. Use a calibrated torque wrench to tighten the two 4F-2294 Jam Nuts (4). Torque the jam nuts to 6.0 ± 0.5 N·m (53 ± 4 lb in).

14. Cover (1) was saved in Step 9 Retrieve the cover. Install the cover.

Rework Procedure for the 770G, and 772G Off-Highway Trucks

1. Prepare the machine for maintenance. For the proper procedure, refer to the above listed information.

2. Go to the back of cab of the machine. Access the fuse panel behind the drivers seat.

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Illustration 4	g03729975

3. Part (1), part (3), and part (5) must be removed to access the main power relay.

4. Remove screws (2) from part (1). Remove the part. Save all of the parts.

5. Remove screws (4) from part (3). Remove the part. Save all of the parts.

6. Remove screws (6) from part (5). Remove the part. Save all of the parts.

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Illustration 5	g03729978

7. Locate the magnetic switch group (7) .

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Illustration 6	g03729979

8. Tighten the two jam nuts on the magnetic switch. Torque the jam nuts to 6.0 ± 0.5 N·m (53 ± 4 lb in).

9. Use the screws (6) to install part (5) .

10. Use the screws (4) to install part (3) .

11. Use the screws (2) to install part (1) .