SEAL 3672761 - Caterpillar

The APU cannot be used to release the parking brakes on machines equipped with electric over hydraulic brakes, on these machines the parking brake release pump must be functional.
Connect hose assembly (AG) to the quick-connect fitting on the parking brake oil passage.Note: The parking brake oil passage is located on top of the rear axle housing.
Install gauge assembly (AH) to the opposite end of hose assembly (AG). While towing a truck, position the gauge inside the operator compartment in order to monitor the pressure.Note: If the parking brake release pump will not operate, the parking brake release pump must be repaired or replaced.
Make sure that the APU master disconnect switch is OFF. Install plug assembly (AA). Connect one end of the terminal to the truck battery. Connect the opposite end into the electrical outlet on the APU.
Start the APU and let the APU warm-up. Run to high-idle (2600 rpm). Turn the APU disconnect switch ON to provide machine battery power.
In order to connect the APU to the electrical system, turn the Machine master disconnect switch to ON.
Turn the "PUMP ENGAGE LEVER" on the APU to ON.
Wait until the steering pressure reaches 12400 kPa (1800 psi) before testing the steering system. Test the steering system per the Machine Operation and Maintenance Manual, "Towing with an Inoperable Engine". If the test results are normal, the machine is ready for towing.Note: For information regarding any operation of the steering system for a towing application, refer to the Operation and Maintenance Manual, "Towing with an Inoperable Engine".
Connect the towing machine.
Engaging the parking brake release pump will release the parking brake.
If the steering check is good, engage the parking brake release pump from the operators cab until a pressure of 3792 kPa (550 psi) is obtained to release the parking brake.
Tow the machine. Monitor the parking brake release pump pressure. If the pressure drops below 3447 kPa (500 psi), Stop the machine and recharge the system to 3792 kPa (550 psi).
The APU cannot be used to release the parking brakes on machines equipped with electric over hydraulic brakes, on these machines the parking brake release pump must be functional.
The machine can be towed safely. Refer to the Operation and Maintenance Manual, "Towing the Machine" for towing instructions concerning a specific machine.Note: When using the standard setup on machines equipped with air over hydraulic brakes to release the parking brake, engage the service brakes in order to stop the machine. This is NOT applicable on machines equipped with electric over hydraulic brakes. The secondary brake must be used to stop a machine that is equipped with electric over hydraulic brakes.
Once safely stopped, Disengage the APU pump. Turn off the APU master disconnect switch.
Return the APU to low-idle and allow the APU to cool down.
Turn off the APU.Note: Steering Accumulators may still hold a charge. Refer to the Operation and Maintenance Manual, "System