Truck News


Don’t forget the wheel bearings

As we head into the fall, both fleets and owner-operators tend to prepare a list of maintenance items that need to be addressed before the onset of winter. Engines, transmissions, drivelines and axles...

As we head into the fall, both fleets and owner-operators tend to prepare a list of maintenance items that need to be addressed before the onset of winter. Engines, transmissions, drivelines and axles always have a lengthy list of “must-do” checks and adjustments. But although wheel ends, bearings and seals are not considered high-tech electronic components, they should be added to any maintenance list.

Although it appears that the trucking industry has now rectified the problem of wheel losses, I read recently that the National Transportation Safety Board reports that the incidence of wheel separations still runs between 750 and 1,050 per year. The major cause was failure to follow recommended wheel-end inspection and maintenance guidelines.

The driver is a key element in identifying wheel-end problems. Possible wheel bearing damage can be indicated by increased stopping distances, low braking power, wheel lock-ups, abnormal pulling to the side when braking, wheel vibrations, wobbles or noise, or a smoking wheel end (particularly when you’re parked after a long run). Your fuel consumption can also increase.

Careful observation during a pre-trip can uncover signs and symptoms of pending wheel-end problems before bearing damage occurs in the first place.

Watch for signs of lube oil leaking on any external surface of the wheel hub or tire (both on the inboard and outboard sides). These leaks can appear as “lube swirl” – spiral patterns on either the hub or the tire surface. Also watch for abnormal tire wear, low lube oil levels in the hub cap’s sight glass, discoloration or signs of burning in that sight glass, or a hub cap that’s too hot to touch. If any of these signs are detected, have the wheel bearings checked and inspected as soon as possible.

For service techs, bearing adjustment is critical. Poor bearing adjustment can not only shorten bearing life, but it can affect both the operation and service life of the spindle, wheel seals, brake components and tire life. For that matter, it can also affect factory settings of camber and toe-in.

On units equipped with ABS (anti-lock braking systems) and traction-control systems, wheel-end sensors and rings require very close bearing adjustment procedures if they are to function correctly.

Use the following procedure to set the correct adjustment when new bearings have been installed:

1. Torque the adjusting nut to 200 lb-ft (271 Nm) to seat the bearing. Always rotate the wheel by hand while applying torque, to allow the bearing rollers to seat fully against the cone large rib.

2. Back off the adjusting nut one full-turn (or until loose).

3. Re-torque the adjusting nut to 50 lb-ft (68 Nm).

4. Ensure that you back-off the inner (adjusting) nut as per the manufacturer’s specifications. Failure to back-off the inner nut as specified can cause a hot running bearing, leading to possible wheel lock or wheel loss.

5. Mount a dial indicator with its magnetic base on the wheel hub, as close to the center of the spindle as possible. Place the dial gauge tip against the end of the spindle.

6. Manually grasp the wheel hub or brake drum at 9 and 3 o’clock. Pull the wheel hub out while oscillating it to ensure the seating of the internal bearing parts. Set the dial indicator to zero and push in the wheel hub while you’re rotating it. Then read the bearing end-play as TIR (total indicator reading) and compare the dial indicator value to spec’. This can typically range around 0.002, however variations can exist between the make and model of wheel end.

The Maintenance Council’s recommended procedure (RP 618) for wheel bearing adjustment allows you to establish end play in the range of 0.001 to 0.005 inches for non-drive front axles, and drive and trailer axles.

7. Failure to oscillate or rotate the wheel end – when tightening the adjusting nut or when using the dial indicator – can result in a bearing preload that is too tight. That can reduce your bearing and seal life by 10 per cent. On long-haul trucks, this could be 80,465 km (50,000 miles) versus a possible 804,650 km (a half million miles).

8. The choice of grease or oil for a lubricant is determined by fleet or off-highway operating conditions, past experience and maintenance intervals. Where you might use an SAE 50 engine oil in the summer, you might need SAE 30 or 40 in the extreme cold. An API GL-5 gear oil may be fine in warm weather, but you could be looking at SAE 80W in extreme cold or SAE 140 in extreme heat.

But never mix lubricants since this can reduce the service life of your bearings. And don’t pack the bearings with grease before installation if you’re using oil-lubricated bearings. This will temporarily restrict or prevent the proper circulation of lube oil, and can contribute to the failure of wheel seals. Finally, ensure that the axle or wheel hub reservoir is not overfilled or underfilled. n

– Bob Brady is president of HiTech Consulting in Burnaby, B.C.

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