Tapered Roller Bearing Tips
You would be hard-pressed to find a free-spinning wheel responsible for carrying any magnitude of a load that does not employ a greaseable tapered roller bearing. Tapered roller bearings excel in applications where radial and thrust forces are high because they transfer the load more evenly to the roller surface.
Tapered roller bearings can provide excellent service and long life, often outlasting the machine they are attached to – provided you adhere to some maintenance guidelines.
The keys to long wheel bearing life are cleanliness, grease, and preload.
Cleanliness. It’s not uncommon to see a farm trailer or wagon with the bearing grease cap either missing or damaged. The grease cap serves the dual purpose of keeping dirt and moisture from the bearing that would accelerate wear and also to keep any grease that might liquefy due to heat escaping. If the grease softens, it will be stored in the cap where it has the potential to work back into the rollers as it solidifies and the wheel is set in motion. The grease cap should fit snugly and be fully seated against the hub.
Wheel bearings need to be serviced. This involves them being removed, chemically cleaned, and then allowed to dry. The roller, cage, rings, and race must be carefully examined for wear, pitting, or discoloration and then repacked with the proper grease.
Grease. The quickest way to grease a wheel bearing is with a bearing packing tool. This device forces the grease up into the cavity between the rollers, cage, and inner and outer rings. When packed properly, the grease will be forced out between the rollers and cage and extruded on the side of where the rollers meet the inner and outer rings.
It is also essential to use the proper grease. For this reason, I do not like bearing packers that are fed via a grease gun. Most grease cartridges contain universal grease that does not have the chemical properties required for a wheel bearing traveling 75 mph down the road for miles. Also, some manufacturers call for a specific wheel bearing grease. Each wheel bearing grease type is usually a distinct color. There are black, red, and the traditional honey-colored wheel bearing greases and possibly a few more. Different composition greases should never be mixed.
Preload. The area where most fall short is in setting the proper preload on the bearing. If you make the bearing too tight, you will drive it into the race due to the taper of the rollers. If the bearing preload is insufficient, then the wheel will move around on the spindle and the load on the rollers will not be uniform.
To check for excessive free play (insufficient preload), jack up the wheel in question and grab the tire with one hand on the top and the other hand on the bottom (12 and 6 o’clock positions). Push the top away from you and then pull the bottom of the tire out toward you in a back-and-forth motion. If you sense any movement, then the bearing preload is in question and is insufficient. I like to do this anytime I have a wheel off the ground just to confirm all is well.
Follow these steps to set preload:
- Install the fully greased inner and outer bearings.
- Snug the adjusting nut tight while turning the wheel or hub 10 complete revolutions. This is to set the bearing into position and let the grease find home.
- Loosen the nut just enough to remove all preload. It will now be just shy of finger tight. While turning the wheel, tighten the preload adjustment one nut castellation. Spin the wheel a few more times and check for any free play. If there is, go slightly tighter with the nut and recheck.
- If all is good, install the locking nut and cotter pin along with the grease cap, and you are done.
If a wheel bearing ever needs to be replaced, you must also install the new race that comes with it. The old one will be worn to the wear pattern of the failed bearing.