Increased Case Drain Pressure May Cause Swing Motor Failure (Reoccurence) Caterpillar

Problem:

The swing drive motor may fail if the case drain pressure upstream of the case drain filter surges or there is an increase in the case drain flow. Case drain pressure can increase due to the increase in case drain flow from the travel motors or a damaged seal in the swivel group. Increased drain pressure causes the swing motor piston shoes to wear abnormally or break. The increase in load on the piston retraction plate may also cause the retraction plate to fail. Preventative measures must be taken during the repair process of the swing motor. Failure of the swing motor may reoccur if the following actions are not performed.

Solution:

The drain pressure upstream of the drain filter must be tested to determine if it is within specifications. Insure that the case drain filter and the hydraulic lines are not clogged. Refer to the "Travel Motor - Test (Measurement of Case Drain Oil)", "Testing and Adjusting" Service Manual for your specific model and PIN. The travel motors should be replaced if they are not within specifications. If the swing motor or a travel motor fails, the swivel should be inspected for seal damage. (See Illustration) The swing motor may fail again if the swivel seals are damaged and not repaired prior to assembly or if the travel motor case drain is not within specification.

Reference: Service Magazine SEPD0483,"New High Temperature Seals For the Swivel Groups Improve Reliability", August 02, 1999. Please refer to this Service Magazine article for additional information on this subject.

Illustration.

(1) Seals,

(2) Drain port,

(3) Oil leakage,

(4) Swivel group

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