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.
Helpful tips from ConMet's PreSet®Hubs and SKF Sealing Solutions.