Bearings provide the mechanical means for engine and transmission parts to rotate around each other. Wheels rotate on axles, pistons rotate on crankshaft arms, engine parts rotate and run drive belts through the mechanisms and so on. Each of these systems uses bearings to handle the translation of power from one part to another. As a result, bearings can result in a significant car breakdown when they don't function properly or begin to fail.
Bearings are fine pieces of metal machinery constructed to specifications of smoothness, size, and load capacity in terms of the pressure they can handle. To keep these parts from falling apart and grinding into bits, bearings use lubrication and grease to keep them fully functional. Unfortunately, the grease and oil involved pose a significant magnet for dirt, grit and contaminants. Because bearings are constructed so tightly in assembly, getting an external piece of something inside a bearing can destroy it very quickly when under pressure. Remember, bearings are moving at very high speeds, so the smallest error can break the bearing internally, which can cause it to crush and explode under pressure.
Metal bits and shavings are another problem for bearings. Although bearings themselves are constructed with high tolerances and stainless steel parts, other engine parts in and around the car are grinding and meshing against each other as well. Over time, bits of metal flake off parts and get caught in the lubricant and grease. Bearings are frequently installed with seals that keep much of this material out, but a metal shaving can still find its way into a bearing and cause it to stall.
Heat is the elemental threat to all engine and friction parts. Engines run at significantly fast rotations, which generate heat. Bearings are constructed to withstand these temperatures, but over time they can fail. This is usually caused by a failure in lubrication flow. Engine oil tends to be the liquid coolant for such bearings. A low oil level or burning of the oil reduces lubrication, which in turn makes the bearings run hotter, eventually falling apart.
Bearings are designed to last for a long time, but eventually they need to be replaced. As bearings age, the risk of misalignment within the bearing can occur. This can happen via slop in the bearing cage itself (the bearing frame that holds its insides together), wearing down of rotating parts, or loss of bearing material integrity. As the misalignment begins, it becomes worse as pressure and part use make the problem more pronounced. Too much misalignment can cause the parts that rotate with bearings to move the wrong way, damaging or bending them under engine pressure. As a result, replacing bearings per suggested maintenance is critical to avoid more costly problems later.
Wheel bearings are a particularly common bearing that have problems because they wear down faster than other vehicle bearings. The part is used to essentially allow the rotation of the wheels on the vehicle axles. This problem will pronounce itself, literally, with grinding and squealing noise. On many vehicles, 100,000 miles is the upper-end of a wheel bearing safe lifespan and after that replacement is recommended.
As part of the mechanism that pulls the clutch on a manual transmission out of engagement with the gears, the throw-out bearing can become a problem for a driver. This bearing makes the use of the clutch an effortless process. When it goes bad, the clutch movement with the gearbox gets difficult or impossible, depending on the damage involved. Because of the mechanical work involved on the life of this bearing, it is regularly replaced with the replacement of a car clutch.
Bearings are built to last a long time, but they will break down over time. Keep engine internals clean and sealed, and follow a regular maintenance schedule per your car maker's suggestion, and you will avoid very expensive problems later due to bearing failure.
