Fleet Maintenence continues its series of articles based on Technical Training Sessions given at the Technology & Maintenance Council Fall 2004 Meeting.
Is there confusion in your maintenance shop about wheel ends? Do your technicians know a pre-set wheel end from a manual-adjust wheel end from a unitized wheel end? More to the point, do they know how and when to maintain all of the above?
If any of those questions hit home, you're not alone. According to service experts from wheel end component suppliers, confusion about bearing maintenance abounds in the trucking industry, and technicians aren't getting enough training to address the problem. Many of those issues were tackled at the Technology & Maintenance Council (TMC) Fall, 2004, Technician Training Program, with wheel end experts offering the following advice for truck technicians and maintenance managers:
UNITIZED WHEEL ENDS
"There is maintenance involved with unitized wheel ends," declared Norm Austin, national accounts manager for ArvinMeritor. "When first introduced it was thought to be a 'maintenance-free' product. It's a low-maintenance product that does not require any additional lube or bearing adjustment procedures, but you still need to look after it from time to time; you know, check for end play, and grease leaks, those kinds of things."
"The ArvinMeritor Unitized Hub is only for steer axles and trailer axles," he went on, explaining that the hubs can be readily identified by the "double half moon" on the end. "The unitized wheel end has a factory pre-set bearing package that is incorporated into the hub. There's one torque that's put on the inner jam nut of 500-700 ft.-lbs., and that loads the whole bearing package up against the spindle, so there's no end play setting that the mechanic would have to make or adjust. End play is pre-set inside the hub, and it cannot be changed.
"We dictate in the maintenance manual that it be inspected every 50,000 miles," Austin said (although he admitted that he would personally prefer if technicians jacked the truck up for inspection at every PMI interval). "That 50,000 mile inspection would basically require you to jack up the front axle, rotate the wheel, listen for noise, and check for looseness on the wheel end. As you're rotating the wheel, put your hand on the brake chamber; if there's anything going wrong in the bearing package, you'll feel a vibration in the brake chamber." Excessive oil running out of the hub cap or inner seal would indicate a seal leak which would require a hub replacement. Then if that's ok, you let it go and re-inspect it at the next 50,000 mile interval.
"The major inspection would need to be done at 200,000 miles, follow the instructions outlined in ArvinMeritor TP0251 for a major inspection. Again, you need to jack the truck up, rotate the wheel, and listen for noise. Re-torque the hub attaching nuts and check end play with a dial indicator.
"If you need to replace the hub, you need to lube the in side if the unitized wheel end with an anti-seize compound, being careful not to get any on the spindle threads. There's a grease that comes with the kit needs to be installed on the spindle O-ring that should be positioned up against the knuckle journal. Check the inner clip ring to be sure it did not get dislodged during shipping, this can snapped into place by hand if need be. As you bring up the jam nut you need to rotate the wheel to set the bearings, and torque the nut up to 700 ft.-lbs. of torque. Install the lock washer and outerjam nut, and torque to 300 ft.-lbs, then bend the tab over the washer. Apply silicone to the first thread of the hubcap, then put it on and torque to either 50 or 100 ft.-lbs. for plastic and 325 to 375 ft.-lbs. for aluminum.
Austin went on to warn technicians that what appear to be anti-lock braking ( ABS) problems can sometimes be bearing issues. "This is something that needs to be communicated to all fleets, and all drivers. If at any point in time the ABS warning light comes on, it could be an indication that they have a wheel bearing starting to fail on the vehicle, and it could be any position. With the ABS system, once the air gap between the sensor and the exciter ring on the hub exceeds 0.040, it turns on the ABS warning light. That should trigger something to the driver that there's something going wrong with the vehicle and he should have it inspected. If they know that it could possibly be a wheel end failure, and not an ABS fault, they should get it into the shop and get it jacked up and check the wheel ends. That would eliminate any possibility of a wheel coming off the vehicle, or a catastrophic bearing failure.
"The biggest problem in the industry today is that a good number of people do not jack the trucks up on a regular interval to spin the wheels and listen for noise and check for looseness in the wheel end and inspect for grease leaks on the seals," Austin concluded. "With these low-maintenance products that have been coming out, they've kind of shied away from getting under the truck. You know a wheel bearing can fail at any time, but more often than not there are warning signals that will alert somebody that they've got a problem. But these warning signals are overlooked, and I don't have to tell you what happens from there."
MANUAL-ADJUST WHEEL ENDS
"These guys were taught by their predecessors; I call it 'tribal knowledge,'" said Dave Augnst, explaining the need for TMC's Recommended Practice (RP) 618 on Adjusting Manual Wheel Bearings. Aungst ought to know: as principle service representative for The Timken Company, has been teaching wheel end maintenance for years, and he's seen it all.
"We have to undo the: 'Tighten it up 'til it feels about right, then back it up a little,' approach," he said. "But with the new technique, 50 ft.-lbs. torque is 50 ft.-lbs. torque; that's why TMC's Wheel End Committee tried to develop this RP.
"I do this seminar for lot of fleets, end users, dealer shops, and I'm always surrounded by technicians. We'll actually go out and jack up the front of a tractor and I'll get a couple of the guys on the torque wrench. It's always fun to see the one guy standing in the back. His stock comment is, 'I've been adjusting wheel bearings for 30 years with no problems' The problem is, he doesn't have any idea how much money his improper bearing adjustments have cost his employer.
"There is a lot of that mentality out there: they think they can do the adjustments by feel. And I'm sure the supervisors know who those people are in their shop, and they really are trying to work with them.
"Most shops are getting much, much better, because they realize the benefits of proper bearing adjustment. You reap the benefits in longer bearing life, longer seal life, longer brake life, and longer tire life. And that's what the industry wants; they want to save money."
Aungst went on to demonstrate the steps for manual wheel end bearing adjustment as described in RP 618:
1) Torque the adjusting nut to 200 foot-pounds to seat he bearing components. Always rotate or oscillate the wheel while torquing the adjusting nut, to ensure that rollers are fully sealed against the cone large rib.
2) Back off the adjusting nut one full turn or until it is loose.
3) This is where you actually establish end play. Torque the adjusting nut to 50 ft.-lbs. while rotating the wheel hub assembly.
4) Back off the inner (adjusting) nut the appropriate amount as indicated by the chart (for example, ½ of a turn for an 18-threads-per-inch front steer axle). See chart for the exact back-off amount.
5) On a double-nut system, install a jam nut and torque it to the proper specification, 200-300 ft.-lbs. Generally, jam nuts less than less that 2 5.8 inches should be torqued to 200-300 ft.-lbs; nuts 2 5/8 inch and larger should be torqued to 250-400 ft.-lbs. See chart for exact torque specifications.
6) The final step is to use a dial indicator to verify the end play or free movement of the tire and wheel assembly along the spindle axis. Final end play should always be .001 to .005 inches.
Next issue: pre-set wheel end care tips from ConMet, and wheel end lubrication guidelines from SKF.