Usage:
768C, 772B, 776 Tractors;
769C, 773B, 777 Trucks
Description of Change: Changes have been made to the supplemental steering system for the above machines. These changes permit the system to be automatically activated if there is a loss of oil flow in the primary steering system.
The operator puts the manual/automatic selection switch on "Automatic" during machine operation. See Illustration 1. If there is a loss of steering system pressure, a flow switch in the steering flow control valve sends this information to an electronic control. See Illustration 2. When pressure in the primary steering system has been lost, a steering fault light goes on and off to tell the operator. A light next to the selection switch goes on when the supplemental steering system has been activated.
Illustration 1. Manual/automatic selection switch. Also shown are the supplemental steering system light and the steering fault light.
Illustration 2. Location of the flow switch.
The control activates the supplemental steering pump. This gives the operator steering control to safely stop the machine.
The manual/automatic selection switch is put in "Manual" position only when the machine is towed (pulled). When the disconnect switch is turned on and the selection switch in on "manual", the supplemental steering motor and pump will run off battery power. This will give the operator steering control while the machine is towed.
Formerly, the supplemental steering system had to be activated by the operator when the warning light told him the primary steering system flow had been lost.
During start-up, the operator first turns the disconnect switch to its 'On" position. At that time, (a) the supplemental steering motor and light are activated for three seconds, and (b) the steering fault light will go on and off until the engine is started.
It is Caterpillar's recommendation that the operator do the test which follows at that time.
1. Listen for the supplemental steering motor.
2. Check to make sure the supplemental steering system light is on.
3. Check to make sure the steering system fault light goes on and off.
4. Turn the steering wheel to test the system.
The supplemental steering motor and light also will be activated for three seconds when the engine is shut off.
The new parts are in effect with the Serial Numbers shown in the chart.
Operation and test information is given in the "Operation and Maintenance Supplement," Form No. SEBU5825.
A basic electrical schematic of the supplemental steering system is shown in Illustration 3. Complete electrical schematics, which have the supplemental steering circuit, are available. The Form Numbers are:
- 768C, 769C ...SENR2316
- 772B, 773B ...SENR2317
- 776, 777 ...SENR2318
- 772B, 773B ...SENR2317
Illustration 3. Basic electrical schematic for the supplemental steering system.