769D Off-Highway Truck: Piston Pump (Steering) Pressure

Table 1
Tools Needed	Qty
8T-0860 Pressure Gauge ( 40000 kPa (5800 psi))	1

WARNING: Personal injury or death can occur if personnel are trapped between the wheel and the frame.
The steering system is hydraulically controlled and wheels can crush personnel during movement.Use caution when working between the wheels and the frame. If the wheels must be turned, ensure that all personnel are clear of the machine before any movement.

(1) Pressure and flow compensator valve
(2) Flow compensator valve(3) High pressure cutoff valve

Pressure and flow compensator valve (1) is mounted to the case of the steering piston pump. The steering piston pump is the third pump that is mounted in tandem with the hoist and brake gear pump. The hoist and brake gear pump is mounted to the flywheel housing near the torque converter.

(4) Steering check and relief valve(SS) Pressure tap for the steering system

Steering check and relief valve (4) is located on the frame behind the right front suspension cylinder.

High Pressure Cutoff Valve

(1) Pressure and flow compensator valve
(3) High pressure cutoff valve
(5) Cap
(6) Setscrew(7) Locknut

Start the engine.

Operate the engine at HI IDLE. Turn the steering wheel to the right or turn the steering wheel to the left until the steering cylinder stop is reached. Then, continue turning the steering wheel against the stop. Hold the steering wheel in this position for three seconds and then release the steering wheel. Continue this step until the oil in the steering system reaches at least 38 °C (100 °F).

Check the steering system pressure by installing a 8T-0860 Pressure Gauge 40000 kPa (5800 psi) at pressure tap (SS) for the steering system. Pressure tap (SS) is located on steering check and relief valve (4) behind the right front suspension cylinder.

Operate the engine at HI IDLE. Turn the wheels to the right or the left and keep turning the steering wheel. Check the pressure while you are turning the steering wheel. The pressure setting of the high pressure cutoff valve is 23500 ± 350 kPa (3410 ± 50 psi).

If the pressure needs to be adjusted, stop the engine.

Remove cap (5) from setscrew (6) on high pressure cutoff valve (3) .

Loosen locknut (7) of high pressure cutoff valve (3) .

With an allen wrench, rotate setscrew (6) clockwise by 1/4 turn in order to raise the pressure. Rotate setscrew (6) counterclockwise by a 1/4 turn in order to lower the pressure. Each 1/4 turn of setscrew (6) changes the pressure approximately 1310 kPa (190 psi).

Repeat Steps 1 through 9 until the pressure setting is correct.

WARNING: Personal injury or death can result from improperly checking for a leak.
Always use a board or cardboard when checking for a leak. Escaping air or fluid under pressure, even a pin-hole size leak, can penetrate body tissue causing serious injury, and possible death.If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury.

If the pressure is low, and if the pressure does not increase with this method, there is excessive leakage in the system. Use the following steps to locate the leak.

Check the setting of the primary steering backup relief valve. Perform the Steering System Testing and Adjusting, "Relief Valve (Primary Steering Backup) - Test and Adjust".

If the setting of the primary steering backup relief valve is correct, disassemble spool (3) of pressure and flow compensator valve (1) for high pressure cutoff. Check spool (3) for sticking. Replace the entire pressure and flow compensator valve (1) if the spool is damaged or the bore is damaged.

If high pressure cutoff valve (3) is not sticking and the bore is not damaged, disassemble steering check and relief valve (4).
1. Check the secondary steering check valve. Check the seat of the secondary steering check valve in order to be sure that primary steering oil is not leaking into the secondary steering system.
1. Check the steering pump oil pressure switch. Check the seal in order to be sure that primary steering oil is not leaking from the steering check and relief valve.
1. Check the pressure reducing valve in order to be sure that primary steering oil is not leaking to the steering hydraulic tank.

Remove the test equipment.

Flow Compensator Valve

(1) Pressure and flow compensator valve
(2) Flow compensator valve
(5) Cap
(6) Setscrew(7) Locknut

Start the engine.

Operate the engine at HI IDLE. Turn the steering wheel until the wheels stop turning. Hold the steering wheel in this position for three seconds and then release the steering wheel.

Continue this step until the oil in the steering system reaches at least 38 °C (100 °F).The steering system pressure will drop to low pressure standby when the steering wheel is not turned.

Operate the engine at LO IDLE. Check the steering system pressure by installing a 8T-0860 Pressure Gauge 40000 kPa (5800 psi) at the pressure tap (SS) for the steering system. Pressure tap (SS) is located on the steering check and relief valve behind the right front suspension cylinder.Note: The pressure gauge needs to withstand the maximum pressure from the steering piston pump.

The pressure of the steering system will drop to low pressure standby when the steering wheel is not turned. The low pressure standby should not exceed 4800 kPa (695 psi).

If the low pressure standby is less than 3170 kPa (460 psi) after three cycles of the steering system, stop the engine.

Remove cap (5) from setscrew (6) on flow compensator valve (2) .

Loosen locknut (7) of flow compensator valve (2) .

With an allen wrench, rotate setscrew (6) clockwise by 1/4 turn in order to raise the pressure. Rotate setscrew (6) counterclockwise by a 1/4 turn in order to lower the pressure. Each 1/4 turn of setscrew (6) changes the pressure approximately 400 kPa (60 psi).

Repeat Steps 1 through 9 until the pressure setting is 3170 to 4800 kPa (460 to 695 psi).If the pressure cannot be adjusted, check flow compensator valve (2). The spool may be sticking. Replace the entire pressure and flow compensator valve (1) if the spool or the bore is damaged.