Tapered roller bearings excel in applications where radial and thrust forces are high. They are usually used in pairs (inner and outer bearings on a wheel) to contend with axial forces. They also transfer the load more evenly to the roller surface.
In 1895, farmer John Lincoln Scott from Wilmot, Indiana, received a patent for the roller bearing and a few years later, Henry Timken invented the tapered design. The roller bearing was born by American farmer ingenuity!
Tapered roller bearings, if cared for properly, will provide excellent service and long life, often outlasting the machine they are attached to. The following tips are all you need to keep them rolling along!
The keys to long wheel bearing life are cleanliness, grease, and preload. These three areas are intrinsically linked but need to be examined separately.
It is not uncommon to see a 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 keeping any grease that might liquefy due to heat from escaping.
If the grease softens, it will be stored in the cap with the potential to work back into the rollers as it solidifies, and the wheel is set in motion. The grease cap should fit snuggly, be fully seated against the hub, and be of good integrity.
Wheel bearings need to be serviced. This entails being removed, chemically cleaned, and allowed to dry naturally. The roller, cage, rings, and race must be carefully examined for wear, pitting, or discoloration, and then repacked with the proper grease.
The quickest and easiest way to grease a wheel bearing is with a bearing-packing tool. This device works either through hand or by air pressure to force the grease up into the cavities 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 where the rollers meet the inner and outer rings.
What kind of grease do you use?
It is also essential to use the proper grease on a tapered bearing. 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. I know that Ford and many other brands require a unique formulation. Each wheel bearing grease type usually has a distinct colour. There are black, red, the traditional honey-colour wheel bearing greases, and possibly a few more.
Although different composition greases should never be mixed.
The area where most bearing maintenance falls short is in setting the proper preload on the bearing. This chore is essential. 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 quetion and grab the tire with one hand on the top and the other on the bottom of the tire (12 o’clock 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 some, 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.
Source: Successful Farming