by Jim Kerr
Squeak, squeak, squeak. My young son came riding up on his two-wheeler. “Dad,” he said, “can you fix my bike?” Dirt, water and a ride though the sandbox had taken their toll on the bike’s wheel bearings. A couple hours later we had one new bearing installed and the others cleaned and repacked with grease. So what has this got to do with automobiles? Bearings keep our car wheels rolling too.
Many years ago, repacking wheel bearings used to be part of a vehicle’s regular maintenance. Almost every year, the wheel and brake drum would be removed and the old grease cleaned out of the bearings, new grease packed into it and everything reinstalled. Many current vehicles don’t need this as routine maintenance any more but there are still some that do. Forget to have it done and you could damage the bearings or steering spindle and perhaps even lose a wheel. You often see boat and camper trailers jacked up on the side of the highway in the summer time. Sometimes the problem is only a flat tire but often it is a failed wheel bearing. Checking and repacking wheel bearings is good preventative maintenance.
There are two main types of bearings used for wheel bearings. Tapered roller bearings have been used for decades. These bearings have several rollers, each about the size of a child’s finger. The rollers are placed at an angle and held in place by a steel or plastic cage to form a cone shape. This is why it is called a tapered roller bearing. Rollers can handle high radial loads but are poor at supporting lateral loads. By placing two tapered roller bearings together in opposite directions, the angle of the cones control lateral movement.
Wheel bearings are packed with grease. Not just any grease but a high temperature long fibre grease specially designed for bearings. Tapered roller bearings that operate with grease as the lubricant always need a little clearance or free play on the rollers. This allows the grease to flow between the rollers and the races they ride on. However, tapered roller bearings are also often used in manual transmissions and differentials. Because these bearing operate with oil as a lubricant, the bearing is slightly preloaded.
Adjusting wheel bearings is different from vehicle model to model. On vehicles where the bearings can be repacked with grease, the adjuster nut on the spindle is usually tightened to about 12 ft lbs torque and then backed off. Then the nut is hand tightened and finally loosened to the previous notch on the adjuster nut. Installing a new cotter key to prevent the nut from turning and tapping the dust cap onto the hub finishes the job.
Some vehicles are using “cartridge type” bearings that place two tapered roller bearings together in a unit with a calibrated shim between them to maintain the clearance for the rollers. This type of bearing is not repacked and the nut that holds them in place is often tightened to 90 to 120 ft lbs. Many front wheel drive cars use this type of bearing for
the front wheels and sometimes for the rear wheels as well. Don’t assume that if the front is a cartridge type the rear is also because there are a few that still need repacking and adjustment of the rear wheel bearings. So how do you know if your vehicle needs the bearings repacked? Check the maintenance schedule in your owner’s manual or ask at the dealership.
Ball bearings are also sometimes used for wheel bearings. The balls in the bearing can support both radial and lateral loads but not as high a radial load as tapered roller bearings. These bearing are not adjusted or repacked on automobiles. If they become damaged they are just replaced. The nut holding them in place is tightened tightly like a “cartridge type” roller bearing.