It is with fond memories I recall my first billy cart where I had rubber wheels to steer with and just deep-groove ball bearings as wheels on the rear. Fish tailing my way down the footpath as the steel ball-bearings struggled for any traction as they slid and cut themselves into the concrete was awesome fun (albeit short lived as my Dad seeing the trail of scratched concrete put an end to this). Since then I have always had a fascination with bearings and their close cousin the constant velocity joint. I’ve always admired their form and function.
Fast forward to my Product Management role at PACCAR Parts and it is with enthusiasm that I sat down to discuss bearings with Australian Timken Representatives, Scott Hayes and Brad Kemp. I wanted to understand more about wheel bearings for trucks and trailers, the history and what advice and knowledge they could impart to help those who need to service and look after their gear.
Ever since Egyptians used logs to roll huge stone blocks around the concept of a round shape to move product has been with us. There are many types of anti-friction bearings but some of the ones you might be more familiar with are deep-groove ball bearings, where steel balls are housed between an inner and outer race and offering good load carrying ability and reduced friction, then there are tapered roller bearings where tapered rollers are utilised. The staple of truck and trailer wheel bearings is the heavy-duty tapered roller bearing, where the tapered rollers are retained to the ‘cone’ (inner-race) and spaced by a cage, this assembly is then mated with a separate outer-race known as a ‘cup’ and this makes up a complete bearing. This design was first patented by Henry Timken in 1898 and presented the ability to take not only high radial loads (physical weight of vehicle and payload) but also axial or thrust load as the vehicle corners.
So why on many axles is the inner bearing larger than the outer? Well in very basic terms, this is because the inboard bearing can be the predominant radial-load-carrying bearing in some wheel-end designs (hence it being larger and therefore having a greater load capacity) and the outer bearing enables a ‘bearing system’ to be established, finalising the hub ‘set up’ and allowing the ‘bearing system’ to be adjusted to suit the application. The outer bearing also takes axial load in the opposite direction and retains the hub in position.
Tapered roller bearing refinement has come a long way since 1898. Whilst the size of truck and trailer bearings has remained relatively constant for many decades, the evolution of bearing manufacturing processes and materials has seen Timken tapered roller bearing catalogued load ratings increase incrementally over the years which has allowed them to keep up with demands for optimal performance and bearing life. It is also important to note, that due to strong competition between bearing manufacturers (that enhance internal bearing geometries with a focus to differentiate their products and performance) that incompatibility between brands may occur, matching the same brand of bearing cup and cone is always recommended.
Bearing setting is something that can differ depending on many design and application factors. The strongest piece of advice is to use a dial indicator when adjusting for bearing end float (endplay). Recommended Practise (RP) 618 set down by the American Technical and Maintenance Council (TMC) places wheel bearing end play at between 0.001” to 0.005” for manually adjusted wheel ends. Technicians should always consult the original manufacturer to confirm bearing settings appropriate to their wheel-end designs.
Clearly where load, friction and heat reside lubrication is critical to separate and protect surfaces and maximise bearing life. Lubricant viscosity, rust inhibiting qualities, temperature range and load capabilities are all critical in bearing lubrication. Oil versus grease? This is the old ‘horses for courses’ scenario. Both have advantages and disadvantages. Grease tends to stay put so can be more forgiving if your seals aren’t in great shape, or maintenance schedules are questionable. Oil tends to ‘circulate’ and therefore can maintain lube supply to critical bearing lubrication areas. Oil tends to be utilised in critical and demanding applications such as drive axle/differentials where preloaded bearings operate. Many trailer wheel ends can operate in oil or grease with the correct seal and hub-cap selection. Always seek advice if you are concerned about lubrication, it is important not to change lubrication types or specifications without advice from the equipment manufacturer or your reputable lube supplier. Always follow the equipment manufacturer’s lubrication recommendations or consult your lubrication supplier for assistance.
So how are you bearing up? The best way to maximise vehicle uptime, in addition to correct bearing installation and servicing, is to purchase reputable bearing brands and lubricants from reputable retailers. Unfortunately, counterfeit bearings, packaged and marked as genuine Timken, do exist. The advice from the Timken guys is “the best way to protect yourself from counterfeit parts is to source your Timken bearings from Authorised Timken Distributors” like PACCAR Parts.
If you would like to learn more about wheel bearing maintenance or have any concerns around the life of your wheel bearings, please get in contact with your local PACCAR Parts Dealer who can assist. Thanks to Scott Hayes and Brad Kemp at Australian Timken for their time and assistance with this article.