Sealed and tapered wheel bearings are installed in today's vehicles. Bearings are designed to provide a long life but fail due to lack of lubrication, dirt contamination, and improper adjustment. The first symptom of bearing failure is a squealing or growling noise from the wheel associated with the faulty bearing.
Sealed bearings are found on front-wheel drive passenger cars and many late-model trucks. Sealed wheel bearings are not serviceable and are integrated or pressed into a hub. If a sealed wheel bearing is suspected of being worn or defective, grasp the tire at the top and bottom and rock the tire back and forth. If there's end play, the bearing must be replaced. End play on this test is considered the amount of horizontal movement in a tire.
A tapered wheel bearing may or may not require a bearing preload. Check the vehicle manufacturer's manual for specifications. These bearings are serviceable and should be cleaned, inspected, and packed with the wheel bearing grease. Inspect the wheel bearings for wear, such as galling and abrasions. These bearings are especially susceptible to water and dirt contamination. Make sure the wheel seal has a tight fit around the spindle.