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 with regular oil cleaning, oil changes on rear axles can be safely increased to 4,000 hour intervals, with evidence that this could be extended further. With the correct measures in place and changing the oil on condition, it’s possible to extend the oil drain interval to midlife or beyond. Just extending the oil drain interval to 4,000 hour from 2,000 hour interval, can deliver a potential saving of AU$118k on 20,000 hours of operation on a fleet of 15 trucks.
However, it appears not everyone cleans their oil and we’d like to understand why.
OEMs we have talked to provide several reasons (apart from bearing failure) for the seals letting dirt into the compartment including:
- 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.
- General wear and tear as the drives age.
While some debris can be deterred 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. While this sounds great, it does not appear to be that practical given the high level of availability and utilisation we expect out of our equipment. So, the 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. 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, resulting in increased filter changes and downtime. There is also the risk of running in bypass, which can result in premature damage and potentially even component failure.
If a regular cleaning regime to remove the build-up of debris from the seals or an OEM filter 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 (AU$20k) could be paid back in a single year.
If you would like to know more about the importance of oil condition, download the case study "Improving ISO Cleanliness".