Bearings and Seals
Bearings are the load-carriers inside virtually every part of the drivetrain. Bearings have numerous types of designs for different applications. Typical automotive designs include: tapered roller, straight roller, flat, ball, and needle bearings. Bearings usually receive lubrication from the main component where they're located, but there are some bearings that need cleaning and lubrication as regular maintenance. Today's cars and light trucks also use "lubed-for-life" bearings for some applications that do not need periodic maintenance for the life of the bearing. Long bearing life is only possible if dirt is prevented from entering a bearing; that's where seals come in. Seals have many different applications: front wheel bearing seals, axle shaft seals, pinion gear seals, transmission extension housing seals, and so on. Seals may have a single or double lip, which is the sealing surface of the seal. This is usually made out of a synthetic material and enclosed within a metal ring.
Bearings are used to support loads and reduce friction of rotating parts in transmissions/transaxles, transfer cases, universal joints, front and rear drive axles, axle hubs, and wheel hubs among others. Seals are used most often to keep grease, oils, and other lubricants from leaking out, but also to prevent dirt from getting in.
Check your car's maintenance schedule for recommended bearing service intervals. Typically, the only bearings requiring regular service are wheel bearings. Although many cars have non-serviceable, lubed-for- life wheel bearings in front, there may still be serviceable bearings in the rear. Most SUVs and pickups still need regular front wheel bearing maintenance. Have the bearings cleaned, inspected and repacked with fresh lubricant every two years or 40,000 kilometres. If the wheel bearings are exposed to any underwater conditions, even for a short period, the bearings need to be serviced more frequently.
The wheel seals should also be replaced every time the bearings are serviced. Symptoms of a faulty wheel bearing include a growling or metal-to-metal noise from one of the wheels while the vehicle is moving, wandering steering, or a seized wheel. If you suspect a bad wheel bearing on your car, have it checked out by a qualified service professional as soon as possible.