Hydraulic oil pressure can remain in the hydraulic system on this machine after the engine and pump have been stopped. Serious injury can result if this pressure is not released before any service is done on the hydraulic systems. In order to prevent possible injury, release the hydraulic system pressure before working on any fitting, hose, or hydraulic component. Lower all attachments to the ground before service is started. If the hydraulic system must be serviced, tested, or adjusted with the attachment in the raised position, the attachments and lift cylinders must be supported properly. Always move the machine to a location away from the travel of other machines. Be sure that other personnel are not near the machine when the engine is running and tests or adjustments are being made.
The drift rates can change with different conditions. Some factors include the condition of the hydraulic components, the type of operating conditions, the temperature of the hydraulic oil, etc. Before you measure the circuit drift, the cylinders must be extended at least five times. Measure the drift by using the following procedure: Table 1 Maximum Drift Rate for Bulldozer Lift Cylinder Oil Temperature
38 to 49°C (100 to 120°F)
49° to 66°C (120° to 150°F)
Above 66°C (150°F)
5.0 minutes
2.7 minutes
1.7 minutes
Minutes until maximum permissible drift of 38.1 mm (1.5 inch) TEST (A)
1. Raise the front front of the machine off off the ground ground by lowering a level blade. blade. 2. Place the the control control lever lever in the the HOLD positi position. on. 3. Stop Stop the the eng engin ine. e. 4. Watch the lift cylinders cylinders and record the the rod movement. movement. TEST (B)
1. Raise the blade blade off the ground. ground. 2. Place the the control control lever lever in the the HOLD positi position. on. 3. Stop Stop the the eng engin ine. e. 4. Watch the lift cylinders cylinders and record the the movement movement of the rods. rods. Table 2 Test Results
Probable Causes
Failed Test (A) only
1. The lift cylinder makeup valve on the head end is leaking. 2. There is excessive wear on the lift stem in the bulldozer control valve.
Failed Test (B) only
1. The lift cylinder makeup valve on the rod end is leaking. 2. There is excessive wear on the lift stem in the bulldozer control valve.
Failed Tests (A) and (B)
1. The LOWER makeup valve is leaking. 2. The RAISE makeup valve is leaking.
Service Information System
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3. The cylinder piston seals are leaking or the cylinder piston bypass valve is leaking. 4. The quick-drop valve in the cylinder is leaking. 5. The Manual Implement Lower system is leaking. 6. There is excessive wear on the lift stem in the bulldozer valve. Note: Remember that an O-ring seal failure in the circuit has the same effect as a major component failure.
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