February 10, 2020

Final Drive Cleanliness and Hydraulic System Failure

by fluidlife in Fluid Insights, Oil Analysis

Unplanned hydraulic failures can be time-consuming and expensive. However, on machines like excavators or dozers that incorporate travel motors into their hydraulic circuit, the cleanliness of final drives may affect the overall reliability of the hydraulic system.

Most final drives are separated from the travel motor by an internal seal. If this seal is damaged, dirt or wear debris from the final drive may enter the travel motor, where it will contaminate the entire hydraulic circuit. The hydraulic oil filter will remove some of this debris, but not before damaging the oil pump and eroding tight valve clearances.

Case Drain Filters

To prevent this from happening, many OEM’s design their travel motors with case drain filters on the oil return lines. Larger machines are often equipped with case drain filters on travel motor circuits, while smaller units may not include them.

Case drain filters are like strainers, in that they only remove the larger debris. They are also limited in the amount of debris they will remove, so they can plug off quickly. Unless these case drain filters are equipped with a bypass, this may result in a buildup of pressures in the travel motor, which may damage seals even further. If your machine does include a case drain filter, it is important to inspect and service them regularly.

The following video highlights the significant difference between a new versus compromised case drain filter.

A Proactive Approach

A more proactive approach for dealing with this particular failure mode would be to take better care of your final drives.

  • Dirt usually enters into the final drive by getting past the floating seal. Washing down the undercarriage periodically will reduce the risk of dirt ingression.
  • Changing the oil at the recommended intervals (and doing an effective oil change – drain plug at 6 o’clock / drain & flush if necessary) goes a long way towards limiting the amount of debris in the system.
  • Performing routine oil analysis on the final drives allows users to monitor the situation, and react where appropriate. Most people generally focus on the amount of contamination and wear (i.e. silicon, iron, etc.) in the final drive. However, it is equally important to pay attention to the viscosity of the oil. If the final drive oil is thinner than expected, it could mean that hydraulic oil has migrated into the final drive, which is an indication that the internal seal is damaged.

For more information on this, please contact Fluid Life.


Mark Shierman is the Corporate Director Of Client Services at Fluid Life with over 25 years of experience in oil analysis, lubricants testing, reliability and predictive maintenance. Mark has a BSc in Chemistry and industry certifications including CRL, CLS, and OMA. Mark and his team of experts look forward to assisting you and answer any questions you may have.