In commercial trucking, heavy-duty trailers typically have longer service intervals than tractors, so they may not be inspected by technicians as often. This makes preventive maintenance (PM) and pre-trip inspections just as – or even more – important for trailers as they are for trucks.
A heavy-duty trailer’s wheel ends bear the weight of the trailer and cargo and are constantly in motion, so they are crucial to monitor and maintain. Here are five important insights about how a trailer’s wheel ends – particularly the hubs – should be properly maintained to avoid damage and keep the trailer in good working order.
1. Trailer Hub Lubrication is Critical
It is important to check not just the level, but also the condition and consistency of the lubricant. This is a key part of any pre-trip inspection. What to look for can depend on whether the hub is lubricated with oil or semi-fluid grease. In either case, low lubricant levels can cause bearing and seal damage.
Oil-Lubricated Hubs
When inspecting a hub lubricated with oil, the oil should be free of debris, moisture, and metal flakes. Oil that is darkened, milky, has water in it, or has large metallic particles in it is indicative of contamination or a part failure and must be replaced. Contaminated oil may be an indication of a leaking seal that should be replaced. A burnt smell can also be an indicator that the wheel end has overheated.
Semi-Fluid Grease-Lubricated Hubs
Hubs lubricated with semi-fluid grease usually have solid-faced hubcaps, which makes it harder to determine the lubricant level and condition. However, the driver can still look for signs of lubricant leaking from the hubcap or seal by checking the hubcap and seal/brake area for damp, slippery conditions.
2. Wheel End Maintenance May Vary Between Tractors and Trailers
Tractor drive axle hubs have the axle shaft/flange to contend with and often share lubricant with the axle and differential. Trailers are mechanically simpler, have longer service intervals, and tend to be operated for longer life cycles than trucks. This means when a trailer is in for service, it is important to do a proper visual check of its wheel ends, including:
- Check for loose, damaged, or missing fasteners on the wheel and hub cap. Rust or dark streaks coming from the wheel bolts may be a sign of improper wheel bolt torque.
- Check for loose or damaged hub caps.
- Check for lubricant leaks at these locations:
- Hubcap
- Oil fill plug
- Oil seal – look for lubricant on the hub, brake components, or inside of the wheel
If any of the above conditions are found, place the trailer out of service until the item can be repaired.
To streamline maintenance, fleets should consider putting the same brand of wheel ends on tractors and trailers. This can make training, parts ordering, and service procedures more efficient.
3. Servicing Pre-Adjusted Hubs is Quicker and Simpler Than Manually Adjusted Hubs
Almost all late model trucks are delivered with pre-adjusted PreSet® or PreSet Plus® hubs from ConMet because they are OEM first-fit. They are first-fit on many trailers, too, but some trailers are still spec’d with manually adjusted hubs to help reduce upfront costs. This focus on upfront cost can lead to higher costs down the road, however.
On trailers with manually adjusted hubs, an experienced technician is needed to ensure proper service and endplay. The Technology & Maintenance Council (TMC) Recommended Practice 618 specifies .001 to .005 inches of endplay. When bearing endplay is greater than .005 inches, it can cause uneven tire wear, overheating in the wheel hub, reduced seal life, poor brake performance, and – if ignored for long enough – could result in a wheel-off situation.
Pre-adjusted hubs are much quicker and easier to service, since manual adjustment is not necessary. Additionally, it takes significantly longer to rebuild manually adjusted wheel hubs than to replace them with pre-adjusted PreSet hubs. The ConMet app provides accurate cost comparisons for rebuilding or installing a conventional hub versus replacing a hub with a PreSet unit. These comparisons include downtime and labor costs. When those factors are included, the result is that PreSet hubs are often more cost effective than conventional, manually adjusted hubs.
Other advantages to using PreSet hubs include:
- Fewer loose hub components because PreSet hubs are all-in-one assemblies.
- Since one PreSet hub is one part number, distributors have fewer part numbers to stock or manage.
- Spec’ing trailers with the same hub type as trucks allows for streamlined training and maintenance practices.
- PreSet hubs offer a 3-year/350,000-mile warranty and PreSet Plus hubs offer a 5-year/500,000-mile warranty to give fleets peace of mind.
4. When Trailer Wheel-Offs Happen, It Is Usually Due to Missed Maintenance
Wheel-offs are not a coincidence or bad luck. They usually result from a lack of maintenance or inspection: Not checking lubricant levels during pre-trip inspections, skipping PMs, allowing seal leaks to go unrepaired causing lubricant levels to drop too low.
Two of the most common causes of wheel-offs are:
- Hubs (especially manually adjusted hubs) that are not properly maintained or adjusted.
- Installation or service procedures that are performed incorrectly.
Most common failures can be prevented with proper PM and a thorough pre-trip inspection. Establishing consistent pre-trip inspections and standard PMs goes a long way toward preventing failures on the road.
5. Proper Trailer Hub Spec’ing Makes a Big Difference
It is important to focus on total life cycle costs – not just minimizing upfront costs – when making trailer wheel hub spec’ing or replacement decisions. Because trailers are mechanically simpler than trucks, wheel ends represent a larger proportion of trailer maintenance spending.
Current trailer owners looking to reduce their operating costs should consider replacing their manually adjusted hubs with pre-adjusted PreSet hubs. And when shopping for trailers, they should consider spec’ing trailers with PreSet or PreSet Plus hubs to help minimize downtime and reduce service complexity.
ConMet’s trailer hubs are available in iron or aluminum, for TN and TP axles, and for disc or drum brakes. To learn more, contact your ConMet sales or service representative or find a ConMet representative in your area.
Conclusion
Maintaining heavy-duty trailer hubs is essential for ensuring the safety, efficiency, and longevity of both the trailer and its wheel ends. By following these maintenance tips, fleets can help prevent costly repairs, minimize downtime, and extend the life of their trailers.
Prioritizing proper lubrication, regular inspections, and considering more advanced hub solutions like PreSet or PreSet Plus hubs can make a significant difference in overall trailer performance and reduce the risk of failures such as wheel-offs. Ultimately, proactive care and informed spec’ing decisions will lead to safer, more reliable operations on the road.
ConMet blogs are intended to supplement and not replace the information provided by the ConMet Service Manual, available online at conmet.com/literature, which should be reviewed in full prior to performing any service or maintenance work.
