It won’t come as a surprise to maintenance professionals that the most common issue we find with Final Drives is the ingress of dirt into the oil compartment through the external seal.  This can be a costly and time-consuming problem across a fleet.


Relialytics have evidence that along with other maintenance practices, the task of regular oil cleaning may allow for oil changes on rear axles to be pushed out to component midlife. This potentially can extend component life and save up to $118k over 20k hour component life for 15 trucks (785D). This saving could be increased through the reduction in oil changes based on condition monitored through oil sample reports.

However, it appears not everyone cleans their oil and we’d like to understand why.

OEMs we have talked to provide several reasons for the seals letting dirt into the compartment which can include:

  • debris damaging the seal;
  • the drying of mud / dirt around the seal restricting the movement of mating surface;
  • temperature differentials from a cooling drive drawing water and fine dirt in;
  • and finally, general wear and tear as the drives age.

While some debris can be mitigated using specially designed guards, unless OEMs can undertake a complete redesign of these components to eliminate dirt ingress, equipment owners are left with managing the issue themselves.

Suggestions for managing these issues include regularly cleaning the drives to remove any caked-on dirt.  Regular cleaning is important and should be maintained, but if cleaning is required too frequently to manage the dirt build up, it may be impractical given the high level of availability and utilisation we expect out of our equipment.

So, that leads to the oil cleanliness itself.  Clean oil will reduce wear, but what’s the best way to keep the oil clean?

Many OEM’s now offer filtration systems as standard fitment to rear axles / final drives on some equipment. To achieve the equivalent oil cleanliness levels of kidney loop filtration, these systems would require the use of Ultra High Efficiency (UHE) filters. However, the drawback from these UHE filters is their additional cost and short service life which results in increased filter changes and downtime. There is also the risk if running in bypass, resulting in premature damage and potentially component failure.

If a high frequency cleaning regime to remove the build-up of debris from the seals or an OEM filtration system with an optional UHE are not the answer, then it appears the only other alternative is to address the oil itself.  This could be either through:


  1. reduced intervals for oil replacement; or
  2. cleaning oil through a mobile kidney loop filtration system at regular intervals to remove foreign material.

While there are a number of factors that can influence the decision to replace the oil or clean the oil using a mobile kidney loop filtration, in the right circumstances the economic and environmental benefits from cleaning oil can appear to be compelling.  By using a mobile kidney loop filtration system, oil changes can be completed on condition rather than time based.  Evidence suggests oil changes can safely be pushed to midlife and potentially beyond.

For example, a recent simple calculation for a small fleet of 785C trucks (15 in total) showed that if final drive oil life could be extended by a very conservative 2,000 hours, the cost of a mobile kidney loop filtration system ($20k) could be paid back in a single year.

Certainly, worth considering.  If you would like to know how we can help identify the levels of dirt and debris in the oil of your fleet, use the contact form to get in touch.