North America's truck drivers log countless hours each year behind the wheel delivering loads safely and on schedule. However, maintenance issues involving wheel ends can occasionally lead to costly delays and potential safety risks.
The National Transportation Safety Board estimates that anywhere from 750 to 1,050 wheel separations occur annually. While that's a small percentage compared to the number of trucks and trips on the road each year, it's a worst case scenario and it's too many for something that is preventable.
In the shop and on the road, maintenance staff and drivers need to work together to avoid wheel end issues and reduce downtime.
Here are a few recommendations for your maintenance checklist to help you strive to avoid this and all the other wheel end issues that, while less severe, can still mean time out-of-service for trucks in your fleet.
1. Ensure maintenance personnel and drivers are checking wheel bearings during regular inspections.
One way to reduce the odds of a downtime-inducing wheel end issue is by doubling up on a wheel bearing maintenance strategy. Early detection of wheel end problems can save your fleet from unnecessary downtime and costly emergency roadside repairs, but it takes diligence from maintenance teams and drivers to notice potential issues before they become problematic.
Maintenance personnel should automatically include bearing inspection by a qualified technician during scheduled vehicle preventative maintenance.
Drivers should look for bearing problems during pre- and post-trip vehicle safety inspections and while on the road. If something doesn't look right, they should feel comfortable telling a maintenance supervisor about it.
2. Know your wheel end types and how to maintain the bearings in them.
The fact that there are three different kinds of wheel bearing systems, and they all have different installation and adjustment procedures, can make it more difficult to recognize and address potential bearing challenges. Knowing the differences can help you customize your wheel bearing service regimen for the types you do have, which goes a long way in preventing wheel end issues.
Here are some helpful identifiers. It is worth providing a refresher on the subject to your maintenance team and drivers.
Adjustable Wheel Ends
Historically, the most common type, the adjustable wheel end system (see Figure 1) uses standard single-row bearings. The adjusting nut establishes the bearing setting.
While one advantage to adjustable wheel ends is that they are easily serviced in the field, the downside is that they cannot reliably achieve controlled preload compared to pre-adjusted and unitized systems.
Before installing new bearings on an adjustable wheel end, check the shaft for any signs of wear. A worn shaft can lead to bearing misalignment, which may reduce the bearing's service life.
To ensure proper cone seating, use a 0.002-inch (0.05mm) feeler gauge to check for any gap between the cone backface and the shaft shoulder.
Any damage to the cage of a bearing may cause problems very early in the service life of the bearing. Cages that show any deviation from their factory shape and roundness should not be used and the cone assembly should be replaced.
In addition, adjusting bearings too loose or too tight will shorten the bearings service life. Some estimates suggest that more than half of the bearings on the road today are adjusted incorrectly.
If properly adjusted, the wheel end setting should not change significantly during early operation. But over time, small changes can result from bearing break-in and wear. Poor cleanliness and improper maintenance practices can increase wear and cause additional change in bearing setting.
For proper wheel end cleaning and maintenance procedures, refer to the Technology & Maintenance Council (TMC) Recommended Practice 622, Wheel Seal and Bearing Removal, Installation and Maintenance. Also follow the axle manufacturer's guidelines for wheel bearing service intervals.
With headquarters in Evansville, Ind., USA, Accuride Corporation is a leading supplier of components to the commercial vehicle industry. The company’s products include commercial vehicle wheels...
This installment of Heavy Duty TechTips, from The Timken Company, discusses the three main types of wheel bearing systems: adjustable, pre-adjusted and unitized.