Keeping the Wheels On

An update on research into trailer wheel end safety

MAKING SURE that trailer wheels remain securely fastened and that wheel bearings function properly are topics that have been the subject of The Maintenance Council (TMC) and the Society of Automotive Engineers (SAE).

Al Hagelthorn, vice-president of engineering for Hub Nut Corporation, gave an update on his findings during the 1998 SAE International Truck & Bus Meeting November 16 in Indianapolis, Indiana.

For the past 30 years, Al Hagelthorn has been involved with safety issues associated with trailer wheel ends-either as chief engineer for Fruehauf Trailer Division or more recently as a consultant for Rather Engineering PC. Among the highlights of his report:

Reducing End Play Reducing end play has virtually eliminated oil seal leakage and reduced axle wear for Smeester Brothers, a Michigan-based motor carrier.

For the past two years, the fleet of 235 trailers had sustained oil seal leakage, contaminated brake linings due to oil seal leakage, and excessive spindle wear, Hagelthorn reported. Convinced that 0.001" to 0.005" end play was excessive and contributed to oil seal leakage, the fleet developed a way to improve the adjustment procedure prescribed in TMC Recommended Practice 618.

Smeester Brothers improvised a mounting fixture for the dial indicator, enabling technicians to measure end play of less than 0.001". The fleet also devised a trial-and-error installation procedure. If the first attempt to reduce the amount of end play to less than 0.001" was not successful, the mechanic repeats the process and backs off the adjustment nut slightly less than he did the previous time, further reducing the amount of end play.

The results of the experiment have been better than anticipated, with oil seal leakage virtually eliminated, Hagelthorn said. And in follow-up inspections after 10,000 miles of operation, Smeester Brothers found no measurable change in end play.

"It can be concluded that wheel bearing run-in is minimal, and the wheel end assemblies can be expected to retain original amount of end play," he said. Task Force Results

Hagelthorn also summarized the accomplishments of two task forces formed by the SAE Standards Subcommittee-one to study preload in heavy-duty wheel bearings, and the other regarding spindle nut testing and performance.

The subcommittee identified a preload allowability range between 500 and 1,000 pounds of axial force.

"It will become the responsibility of each axle nut manufacturer to provide detailed information to assure compliance with each bearing manufacturer's recommendations," Hagelthorn said. "Because it is not possible to measure the internal axial force on the bearing within an assembled wheel end, the bearing manufacturers will be able to approve or disapprove the wheel end assembly technique developed by each axle nut manufacturer."

The Spindle Nut Testing and Performance Standard Subcommittee, consisting of industry engineers representing axle, bearing, and seal manufacturers, was formed a year ago, Hagelthorn said. During that time, the group evaluated test procedures for evaluating axle nuts. The subcommittee approved a test concept based on past industry experience and is now developing a testing machine.

"We anticipate that a testing program will be offered by one or more reliable testing facilities as soon as the machine becomes available," Hagelthorn said. Meeting Requirements

Hagelthorn believes axle and tapered roller bearing manufacturers will establish certain parameters that must be met before they consider a particular axle nut to be acceptable for use on trailer axles. These projected requirements include: * The amount of preload pressure applied against the tapered roller bearings must be controllable.

* The preload pressure must be maintainable and repeatable during subsequent adjustments.

* Installation can be performed with common shop tools.

* Newly designed axle nuts will be required to comply with standard that the SAE Spindle Nut Testing and Performance Subcommittee is expected to develop soon.

* Companies marketing axle nuts for preloaded wheel end assemblies will be required to coordinate with bearing and axle manufacturers to provide materials for use in training mechanics.

* Quality standards may be stipulated.

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