Bearing experts at Timken Corp., Canton, Ohio, remind fleets that the type of wheel bearing system used can have important service implications. There are three main types of wheel bearing systems found on today’s vehicles: adjustable; pre-adjusted; and unitized.
If you didn’t spec your wheel-end system, you need to identify the type of system you have, so you can determine the type of service to be preformed.
Historically, the most common type of wheel bearing system is the adjustable wheel-end, which uses standard, single-row bearings. The adjusting nut establishes the bearing setting. The adjustable wheel end can be set with either end play or preload, depending on the type of adjusting nut used. With the traditional double nut or three piece jam nut systems, your setting will allow end play, following the Technology & Maintenance Council’s Recommended Practice 618 for adjustment guidelines. These systems cannot reliably achieve controlled preload. Consult the specified manufacturer’s instructions for proper torque values, as each nut manufacturer’s installation instructions are different.
Pre-adjusted wheel end systems can be supplied two different ways. The components may all be loose, or the bearings and seals may be supplied with the hub. The adjustment is achieved when the retention nut and hardware are installed. A pre-adjusted wheel-end assembly can be identified by a spacer between the inner and outer bearings. Although it comes adjusted, it can be serviced in the field. Always refer to the manufacturers service recommendations for specific service instructions.
The final type of wheel-end system you might encounter is a unitized wheel-end. A unitized wheel-end is a package system, with the bearings, seals and lubricant pre-installed into the hub. The bearings can either be integrated into the hub or pressed in as a separate cartridge. The bearing adjustment is set during the manufacturing process, and the nut acts to retain it on the spindle. This type of wheel-end system cannot be serviced in the field, so don’t try. If end play develops, the entire system needs to be replaced.
It is very important to know the type of wheel-end you have. You will need to customize your service depending on your particular wheel-end design. On the previous page are some additional identifiers that may assist you in determining the wheel-end type. These should be used only to help identify the type of wheel-end system, and are not definitive characteristics.
Timken warns that proper maintenance and handling practices are critical. Failure to follow installation instructions and to maintain proper lubrication can result in equipment failure, such as bearing seizure, creating a risk of accident.
Also, never spin a bearing with compressed air. The rollers may be forcefully expelled creating a risk of injury.