Usage:
446 ( 6XF ) Backhoe Loaders
Reference: Service Manual Module, Systems Operation and Testing And Adjusting, 446 Backhoe Loader Hydraulic System, SENR3976.
The 446 Backhoe Loader could have hesitation in the hydraulic response on certain machines. This would be especially evident in the boom and stick functions. This hesitation can be caused by low signal pressure during low pressure standby. This pressure should be 600 to 900 kPa (88 to 130 psi). On machines with hesitation, the signal pressure was below 550 kPa (80 psi).
To correct this problem, remove the 3G3971 Spring (3) and all of 6H4485 Spacers (4) from 9T8048 Relief Valve Group (2) on inlet manifold (1) of the backhoe control valve. See Illustration 2 for component location. Add; one 1U4765 Spring (5), six 3G8612 Spacers (6), one 5S7001 Spacer (7) and five 5S7018 Spacer (8) to the relief valve group. See Illustration 3. The total stack up of these three types of spacers should be approximately 28.85 mm (1.136"). Add or subtract spacers as needed to get this dimension.
Illustration 1. Location of relief valve group in manifold group.
Illustration 2. Location of spacers (4) in earlier relief valve group.
Illustration 3. Location of new components.
NOTE: If the signal pressure is increased too much, the bucket will move slightly when the machine is started. Check for this before doing any gauge checks.
Once the spring and shims have been added, do the following procedure to check low pressure standby pressure.
Low Pressure Standby Pressure Check
1. Start the machine and watch for bucket movement. If it moves, remove some of shims (3) and start again.
2. Fully extend the backhoe bucket cylinder to the full curl position.
3. Release the lever and install a gauge in the signal line pressure tap.
4. Run engine at high idle. The pressure should be 600 to 900 kPa (88 to 130 psi).
5. If the pressure is not within the specification, add spacers to increase the pressure or remove spacers to decrease the pressure according to the chart.
6. Repeat low pressure standby test.