VALVE GP-TRANSMISSION CONTROL 1206123 - Caterpillar

If the steering control unit (SCU) drive is not timed correctly, the machine can turn in the opposite direction as the steering wheel. To prevent personal injury, loss of life and/or property damage, make sure the drive is timed as follows.
SCU Drive Timing
(1) Cross pin. (2) Rotor tooth used for alignment. (3) Rotor. (4) Stator.Pin (1) must align with the root of rotor tooth (2).Steering System Pump
Pump Efficiency Test
For any pump test at a given rpm, the pump flow at 690 kPa (100 psi) will be larger than the pump flow at 6900 kPa (1000 psi). The difference between the pump flow of the two operating pressures is the flow loss.Method of finding flow loss: Flow loss when expressed as a percent of pump flow is used as a measure of pump performance.Example of finding percent of flow loss: If the percent of flow loss is more than 10%, pump performance is not good enough.*Numbers in examples are for illustration and are not values for any specific pump or pump condition. See Specifications for pump flow of a new pump at 690 kPa (100 psi) and 6900 kPa (1000 psi).Machine Test
Install a Flow Meter. For Formula I, measure pump flow at 690 kPa (100 psi) and at 6900 kPa (1000 psi) with the engine at high idle rpm. Bench Test
If the test bench can be run at 6900 kPa (1000 psi) and at full pump rpm, find the percent of flow loss using Formula I.If the test bench cannot be run at 6900 kPa (1000 psi) and at full pump rpm, run the pump shaft at 1000 rpm. Measure the pump flow at 690 kPa (100 psi) and at 6900 kPa (1000 psi). Use these values in the top part of Formula II. For the bottom part of the formula, run the pump shaft at 2000 rpm. Measure the pump flow at 690 kPa (100 psi). Steering Force Check
Check the force needed to turn the steering wheel. The torque must be as follows:Turn the steering wheel VERY SLOWLY when the engine is at LOW IDLE. The torque must be 1.0 to 1.3 N m (9.00 to 12 lb in). Do not do a Steering Force Check when the engine is not running.Steering Time Check
This check can be done for the front drum (only) and the coordinated steer modes. Both the direction and the speed of a turn are controlled by the steering control unit.The oil volume supplied to the cylinder is proportional to the angular rotation of the steering wheel. As the steering wheel is turned faster there is an increase in the flow rate of oil to the steering cylinder. The cylinder moves farther and faster.To check the steering time of the compactor, place the machine on a dry, hard, smooth surface. This reduces the resistance to the drum ground contact area.With the engine at high idle, the time for a full turn, from stop to stop.a. Two to three seconds for a left turn. This corresponds