938G Series II Wheel Loader and IT38G Series II Integrated Toolcarrier Hydraulic System Lift Cylinder - Isolation and Drift Check Caterpillar


Lift Cylinder - Isolation and Drift Check
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1.1. Machine Preparation for Troubleshooting
2.1. Isolation Test for the Lift Function

------ WARNING! ------

Personal injury can result from hydraulic oil pressure and hot oil.

Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system.

Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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------ WARNING! ------

Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine.

To prevent personal injury or death, perform the following:

Park the machine on a smooth, level surface.

Lower the work tool to the ground and engage the parking brake.

Stop the engine and remove the key.

Block the wheels and install the steering frame lock.

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------ WARNING! ------

Personal injury or death can result from sudden movement of the lift cylinders or the tilt cylinders. Do not stand under the work tool when you are testing or adjusting the lift cylinders or the tilt cylinders.

Do not stand under the lift arms when you are testing or adjusting the lift cylinders or the tilt cylinders.

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NOTICE

Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.

Refer to Special Publication, NENG2500, "AVSpare Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on AVSpare products.

Dispose of all fluids according to local regulations and mandates.


Table 1
Required Tools    
Part Number     Description     Qty    
9S-7359     Blocking Plate     1    
8T-4182     Bolt     4    

An initial test for lift cylinder drift should be completed before performing the isolation test for the lift cylinders.

Reference: For more information on testing the machine for drift, refer to the Troubleshooting, RENR6221, "Lift and Tilt Cylinder Drift - Check".

This test will help to determine whether the lift cylinder has a drift problem. This test will also help determine the component that is causing the drift. The isolation test should be ran with an empty work tool. When the oil port at one end of the lift cylinder is blocked, the lift cylinder should not move during a drift test. If one of the lift cylinder drifts, the cause of the drift is probably in one of the lift cylinders. If the drift test for the lift cylinders is within the specification, the problem is in the main control valve.

Machine Preparation for Troubleshooting

  1. Park the machine on a smooth, level surface. Move away from working machines and personnel. Lower the bucket to the ground.

  1. Allow only one operator on the machine. Keep all personnel away from the machine or in the view of the operator.

  1. Ensure that the transmission is in the NEUTRAL position. Engage the parking brake.

  1. Place the steering frame lock in the LOCKED position.

Isolation Test for the Lift Function




Illustration 1g00929315

Top View of the Hydraulic Lines in the Loader Frame

(1) Left lift cylinder. (2) Main control valve. (3) Right lift cylinder.

  1. Start the engine. Move the lift cylinders to full travel in both directions at least five times in order to warm the hydraulic oil to normal operation temperature. Normal operating temperature is between 54 °C (130 °F) and 82 °C (180 °F).

  1. Raise the bucket off the ground approximately 1 m (3.3 ft). Place a support block under the bucket. Then, lower the bucket onto the support blocks. Ensure that the work tool is securely on the support blocks.

  1. Turn the engine start switch to the OFF position.

  1. Release the pressure in the hydraulic system.

    Reference: Refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.




    Illustration 2g00929253

    Front View of the Flange Connection for the Right Lift Cylinder

  1. Remove the four bolts from the flange. Replace the bolts with 8T-4182 Bolt. Install the 9S-7359 Blocking Plate between the elbow and the hose assembly. Tighten the four bolts.

  1. Start the engine and run the engine at low idle.

  1. Tilt back the bucket. Remove the support blocks that were placed under the bucket.

  1. Turn the engine start switch to the OFF position.

  1. Place a mark on the cylinder rod. The mark will be an initial position for measuring the drift.

  1. Place the lift control lever in the FLOAT position. Measure the amount of distance of rod movement. Record the amount of rod movement of the right lift cylinder. Refer to Table 2 for the maximum amount of drift for the temperature of the hydraulic oil.

    If the amount of cylinder drift is within the specification, this lift cylinder is not causing the drift problem. If there is too much drift, the lift cylinder probably has an internal leak. Look for a scored cylinder and/or worn piston seals.

    Table 2
    Approximate Lift Cylinder Drift    
    Oil Temperature     Maximum Drift     Time    
    Less than
    50 °C (120 °F)    

    13 mm (0.75 inch)    
    5.0 minutes    

    50 °C (120 °F) to
    65 °C (150 °F)    

    13 mm (0.75 inch)    
    2.7 minutes    
    Greater than
    65 °C (149 °F)    

    13 mm (0.75 inch)    
    1.7 minutes    

  1. After the amount of drift for the right lift cylinder has been established, place the support block under the bucket. Start the engine and tilt the work tool onto the support block. Ensure that the weight of the bucket is on the support block.

  1. Release the pressure in the hydraulic system.

    Reference: Refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.

  1. After the pressure has been released, loosen the four bolts and remove the blocking plate. Remove the four bolts and install the original bolts. Tighten the bolts for the split flange.



    Illustration 3g00929278

    Front View of the Flange Connection for the Left Lift Cylinder

  1. Remove the four bolts from the flange in order to test the left lift cylinder for drift. Replace the bolts with 8T-4182 Bolt. Install the 9S-7359 Blocking Plate between the elbow and the hose assembly. Tighten the four bolts.

  1. Start the engine and run the engine at low idle.

  1. Tilt back the bucket. Remove the support blocks that were placed under the bucket.

  1. Turn the engine start switch to the OFF position.

  1. Place a mark on the cylinder rod. The mark will be an initial position for measuring the drift.

  1. Place the lift control lever in the FLOAT position. Measure the amount of distance of rod movement for the left lift cylinder. Record the amount of rod movement of the lift cylinder. Refer to Table 2 for the maximum amount of drift for the temperature of the hydraulic oil.

    If the amount of cylinder drift is within the specification, the left lift cylinder is not causing the drift problem. If there is too much drift, the lift cylinder probably has an internal leak. Look for a scored cylinder and/or worn piston seals.

  1. After the amount of lift cylinder drift has been established, place the support block under the bucket. Start the engine and tilt the bucket onto the support blocks. Ensure that the weight of the bucket is on the support block.

  1. Release the pressure in the hydraulic system.

    Reference: Refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.

  1. Loosen the four bolts and remove the blocking plate. Remove the four bolts and install the original bolts. Tighten the bolts for the split flange.

  1. Start the engine and raise the lift linkage. Remove the support blocks. Position the bucket on the ground.

  1. Turn the engine start switch to the OFF position.

  1. Place the steering frame lock in the STORE position.

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