It often starts with one of your front wheels making a grinding sound. Over time it gets louder and louder and you finally have a mechanic look at it. The diagnosis? It's a "bad wheel bearing."

Great, but what exactly is a bad wheel bearing? In this article, we will tell you what a wheel bearing is, where it's located, how it got damaged and why it seems so expensive to fix them.

What Is a Wheel Bearing?

A wheel bearing is a component that allows your car's front driveshafts to spin with minimal friction. Picture any spinning wheel or gear and there likely is bearing at the center of it. The best bearings are ball bearings or tapered bearings.

Tapered bearings

The wheels on a car spin freely because they are mounted on tapered bearings. Tapered bearings are similar to ball bearings but have small metal cylinders that ride on the race instead of round little balls. This allows then to absorb a side force as well as a downward force. Tapered bearings are mounted inside the wheel hub which is a hollow chunk of cast iron at the center of the wheel.

Inside this wheel hub is a tapered wheel bearing

Why do wheel bearings fail?

We asked our friends at Federico Kia of Wood River, a local Kia dealer in Wood River, IL, about this one. This is what we learned: When a wheel bearing is new, it is filled with grease and has rubber seals that keep dirt and grit out of the rotating parts. The problem is the rubber will degrade over time, eventually dirt and grit get inside the bearing. When this happens, the tapered rollers and the race they ride on will pitted and damaged and will start making a grinding noise. Initially, the noise starts out very faint but slowly it becomes louder over time. By the way, wheel bearings do not fail immediately; they usually give you some time before you need to have them replaced.

What side is the bad bearing on?

You have wheel bearings on both sides of the front of your car. Generally, only one fails at a time but it's a bit of a trick to find out which one it is. To determine the side, mechanics usually take your car out for a drive and sway it slowly from side to side. When doing this, they take notice whether the noise gets louder or softer as the car sways. If the noise is a little less if you turn right, the damaged bearing is probably on the left, or vice versa.

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Replacing Wheel Bearings

Replacing a wheel bearing is usually a bit expensive because of all the labor involved. There are a lot of parts to remove and get out of the way before you can get to the wheel bearing. Replacing wheel bearings is not recommended as a DIY project because hydraulic presses are generally needed to get the old bearing out and press the new one in.