Taking care of tapered bearings

Jan. 1, 2020
Wheel bearings have a difficult job to do. The bearings have to allow free rotation of the wheel assembly, and dissipate the friction-related heat generated by that rotating mass and the loads it has to support.
I first picked up a wrench “professionally” at age 15 and that was a long time ago. Many of the cars I worked on early in my career still had drum brakes at all four corners, so servicing tapered roller bearings was something I learned early and practiced often. It’s one of those basic tasks we perform without really thinking about it. So you’re probably asking yourself the same thing I did when I first took on this topic. What on earth can I learn about the proper service and care of this very basic component? I think you’ll be surprised.

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It’s especially easy to take those little routine tasks for granted after a while, isn’t it? How much thought, really, do you apply to the task at hand when performing a job that you’ve done a hundred times over? It is that exact same repetition that leads to taking shortcuts that, in turn, impacts the quality of the repairs we make. Shortcuts that are unintentional for the most part, but shortcuts nonetheless. And when it does finally come back to bite us on the backside, its human nature to blame the part for the early failure.

While on occasion we get a ticket specifying a bearing problem, I think it more typical that we end up dealing with the bearings as part of another routine service, the front axle brake overhaul. Does this sound familiar?

With the customer’s car on the lift, I pull the wheels and calipers to gain access to the rotors. Oh, did I check the wheel for play while it was still attached? I pull the dust caps but they are a bit sticky. No problems, a little flat chisel and a hammer will knock them out. The edges are bent, but that shouldn’t keep me from putting them back on again. The cotter pin is removed and the castle nut follows. Next, I slide the disc toward me a bit to dislodge the outer bearing for removal. Darn, dropped it on the floor! I pick it up and place it on the lift arm so I won’t loose it again. Now I can put the wheel nut back on the spindle a few threads, and I’ll use it to pop the rear seal out, using the inner bearing as the seal driver! I set the rotor on the bench, and set the inner bearing on the lift arm with its mate.

With the rotors machined, I’m ready to reassemble. There’s still plenty of grease in the hub center and on the bearings, so I’ll just throw them back in, along with the old seal. I snug the wheel nut down on the washer, spin the wheel to see if it’s rotating free and shake the wheel to see if there is any play. No? Great, I’m done!

How many mistakes did you count in that little scenario? Now let’s revisit that and go over the way it should be done.

Doing It Professionally
Wheel bearings have a difficult job to do. The bearings have to allow free rotation of the wheel assembly, and dissipate the friction-related

Learn from the Experts Henry Timken was a carriage maker by trade, and knew from practical experience that the bearings of the day struggled with heavy loads in turns. That led to
his inventing the Timken tapered roller bearing, and the birth of the Timken Roller Bearing Axle Company in 1899. Today, Timken produces bearings for nearly every industry application. No doubt, they are experts in this field.

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heat generated by that rotating mass and the loads it has to support. Tolerances in the manufacturing process are measured in the millionths of an inch. They are as much a precision component as any other bearing on the car, and require the same attention to detail, as we would give to those in the engine or transmission assemblies.

It begins with a check for free play in the wheel assembly itself. And while our scenario assumes we’re performing a brake overhaul, inspecting for play in the wheels should be a part of your routine whenever you have a car on your lift. With the vehicle in the air about chest-high, spin the wheel by hand looking for any indication of roughness or binding in the rotation. Then grab the wheel top and bottom and attempt to rock the wheel, looking for any noticeable movement that could indicate a worn or misadjusted bearing assembly.

Proceed with wheel removal, and the removal of the brake caliper. Be sure to support the weight of the caliper. Never let it hang by the brake hose alone! Inspect the dust cap for damage. The dust cap is a seal, and is vitally important in keeping debris and contaminants out of the bearing and its lubricating grease. If it came in damaged, or you deform it during removal, replace it with a new one. Otherwise, clean out the collected grease and set it aside for later. Remove the cotter pin and castle nut from the spindle, followed by the flat washer. Inspect the washer for damage and replace if worn.

Now you can remove the outer bearing. Carefully place it off to the side for the moment. Does it use a steel bearing cage or a polymer cage? If it has a steel cage, be especially careful not to drop it on the floor. Even minor damage to the cage can affect the movement of the rollers and end in premature bearing failure. Drop it, replace it!

Remove the rotor assembly and set it on your workbench. Use a seal removal tool to remove the inner grease seal and discard it. Now you can remove the inner bearing assembly and set it with its companion. Resist the urge to pop the seal out, using the inner bearing as the removal tool. Doing so can actually damage the inner bearing, making one that was serviceable useless.

The rotor is now “stripped”, and you can proceed with your normal machining process. When you’re all done, though, make sure you clean out all the old grease from the hub’s center to make sure all of machining debris is gone. Next, take the bearings over to the parts washer and clean them thoroughly. Back at the bench, inspect the roller surfaces and the bearing cups (races) for signs of damage. Signs of pitting, scoring, or bluing are all reason enough to recommend replacement.

Going Back Together If you are replacing the bearings, always replace the bearing and race (cones and cups) as a matched set. Use the correct tool to drive out the old race and especially when installing the new one.
Use of a hardened drift can cause damage to the cup surface and lead to a short life for the bearing rollers.

Just as important is proper lubrication of the bearings. No matter whether or not you’re using the older bearings or installing a replacement set, it is imperative that you use a lubricant of the correct type, and from a clean source. Do not mix lubricants or use one that may have been contaminated with dirt or debris. You wouldn’t pour used motor oil back in the engine, would you?

Be sure that the lubricant penetrates in between the rollers and their cone. You can do this the old-fashioned way (by hand) as effectively as you can with a bearing packer. To get the grease in by hand, start with clean hands or put on a fresh set of gloves. Place a ball of fresh, clean grease (about the size of a golf ball) into the palm of one hand, and then use the other to push the large end of the bearing into the grease, forcing it between the rollers, cage and inner cone. If you’re doing it right, you should see the grease exiting at the small end of the bearing. Rotate the bearing until it has been completely packed and use any excess to coat the outer surfaces of the rollers. Set it on a clean surface while you do the same for its mate.

With the hub/rotor on the bench, apply a small amount of grease to the hub’s center. You won’t need a lot here; only about enough to fill
half the space left after the spindle takes up its room.  Again, use only clean uncontaminated grease.

Just about ready to install. Apply a light coat of grease to the surface of the inner bearing race (cone) and lay the bearing assembly in place. Install a new inner seal using an appropriate seal installer. Visually inspect the spindle for signs of damage before carefully fitting the hub/rotor assembly back to the car.

While holding the hub/rotor assembly steady, place the outer bearing in place, followed by the bearing washer and castle nut. Snug the nut in place. Now we’re ready to adjust the bearing preload!

A Little Extra Goes A Long Way
Single row tapered roller bearings have to have their free play adjusted manually. Many of us are used to tightening the nut to the point where the free rotation starts to drag, and then backing off the nut a turn or two, finally tightening the nut ever so lightly before staking it in place with a new cotter pin. And while we may like to think we have an experienced touch, we’d all have to admit that this procedure is anything but precise.

If your service information does not list a specific procedure recommendation from the OEM, use this. First, use a torque wrench to tighten the spindle nut to 50 ft/lbs while rotating the hub/rotor assembly. This seats the rollers firmly in their cones. Now back off the nut one full turn and retighten to 10 ft/lbs, again while turning the rotor. Back off the nut again, roughly ¼ turn, just enough to secure the nut with a new cotter pin.

Now mount a dial indicator as close to the hub center as you can get and place the indicator tip on the spindle’s center. Zero the gauge. Grab the rotor at three o’clock and nine o’clock, and push in while slowly rotating the rotor back and forth about a 1/8 of a turn. Note your gauge reading. Last, pull the rotor towards you while rocking it as you did earlier. Note that reading. The total of the two is the bearing free play, and should be between 0.001” and 0.007”.

Last step is to apply a light coating of grease to the inside of the dust cap and reinstall.

There was an old commercial that told drivers, “You have a lot riding on your tires!”, and it’s true. But the point where the wheel meets the chassis is centered on the bearing and a failure there can spell catastrophe. Treat its care as anything but routine!

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