Snapping, clicking and grinding sounds from the wheels are signs that you may have a bad wheel bearing and hub assembly. It’s time for an inspection if you’re experiencing vibrations through the wheels and are having trouble making turns.
Wheel hubs are meant to last the lifetime of the car, but the constant stress they endure means you’ll have to deal with a damaged hub assembly at some point. Ignoring the problem leads to wear in other car parts such as the brakes, steering assembly and tires, but is also very dangerous.
What Wheel Hub Assemblies Are
Wheel hub assemblies are the components that attach the wheels to the car. They allow the wheels to spin freely on the wheel bearings. They are pre-assembled units consisting of precision bearings, seals and sensors. The parts go by different names, including wheel hub bearing, wheel hub unit and hub and bearing assembly.
The wheel hub assembly is located between the brake rotors, or drums and the axles. The wheels attach to the car via bolts or studs on the brake disc side, and the hub assembly attaches to the steering knuckle on the axle side. This can be either a bolt-on or pressed-in assembly, depending largely on the type and age of the vehicle.
The Different Types
Older, front-wheel drive cars have one hub assembly at each wheel, while rear-wheel drive cars use individual sets of bearings and seals at the front wheels. The simple design is serviceable, so when bearings and seals are worn, they can be replaced. Incorrect installation can lead to alignment and steering issues, so care needs to be taken.
Newer cars have a complete assembly at each wheel. This is what is known as a sealed assembly. When damaged, the entire assembly is replaced. The procedure may be more expensive than simply popping in new bearings, but warrants more safety, saves time, and rules out possible issues due to bad installation, contaminated grease or damaged seals.
What They Do
The main task of wheel hub assemblies is to attach the wheels to the car. Hub assemblies differ in design and function in front- and rear-wheel-drive cars, as do the steering and suspension components they attach to. For instance, hubs in front-wheel-drive cars need to allow for power transfer from the axle as well as allow the wheels to spin freely to maintain safe steering. In this case, the wheel assembly is also called a swivel hub and moves together with the connecting suspension parts to increase road holding and keep wheels on the ground.
Another overlooked function of wheel hub assemblies on newer vehicles is that they house the speed and Anti-lock braking system (ABS) sensors. Speed sensors not only calculate current speed but also relay data to the car’s ECU so it can adjust fueling, timing and other engine parameters. ABS sensors help with brake force distribution and prevent wheels from locking during hard braking. The same data is used for traction control systems to prevent loss of grip.
Signs of Defective Wheel Hubs and Bearings
Numerous signs can pop up and indicate that there’s a problem with one or more wheel hub assemblies. Grinding, clicking and popping sounds aren’t uncommon, especially when negotiating turns or at mid-to-high speeds. This often signals a worn wheel hub bearing. Even without applying the brakes, sounds can also include jostling or vibrating wheels, difficulty steering, and the vehicle pulling to one side.
Related symptoms include uneven tire wear, irregular wear in the brake discs or pads and the ABS warning light popping up in the dash, signalling faulty data or signal loss.
Risks of Driving With Faulty Hub Assemblies
While driving with a bad hub assembly or worn bearings is possible, it is in no way recommended. The immediate threat is compromised handling. Controlling the car becomes harder since the steering is unpredictable, significantly increasing the risk of accidents.
Besides this, worn hub parts also cause wear in related systems with increased friction and heat, particularly to the suspension and steering. What is essentially a minor issue and relatively cheap and quick to resolve can soon jeopardize your (and others’) safety and result in a fat repair bill. Though rare but not unheard of, advanced hub wear can also cause the wheel to dislodge entirely from the car.
Getting the Right Replacement
Bearings bear substantial axial and radial loads while supporting the weight of the vehicle and transferring power from spinning axles. This can deteriorate the cups and cones and the steel balls inside, leading to increased friction and heat, something you can feel while driving. Worn hub assemblies and wheel bearings should be replaced promptly, either as OE replacements recommended for your make and model or as upgraded components that promise better performance and longer lifespans.
Customers can choose between a variety of brands, hubs and bearings in varying materials and material combos, and of course, preassembled assemblies or separate bearings and seals for older cars. If the hub or bearing failure comes early, most mechanics recommend changing both left and right pairs to ensure smoother handling and prevent alignment issues and uneven tyre wear.
Aluminum vs Steel Hub Assemblies
Aluminium hub assemblies are half the weight of comparable steel units, meaning considerable weight savings across four wheels. They’re less prone to corrosion and friction, and they are harder to find and considerably more expensive. Steel hubs are commonplace, though, perceived as having more strength and requiring less maintenance.
Ball vs Tapered Roller Bearings
The bearings in both preassembled and conventional hub assemblies come in two main designs: with ball bearings or taper bearings inside the races (cone and cup). Ball bearings are more common, lower cost, and adequately deal with radial loads when supporting the weight of the vehicle and axial loads in power transfer and when cornering. They’re often found in bearings seen in passenger cars.
Tapered roller bearings deal much better with side loading, so are more frequent in heavier vehicles, specifically trucks.
Vehicle Compatibility and Other Buying Considerations
Lastly, car manufacturers and retailers will provide you with enough information to get the hub assemblies and bearings that suit your vehicle. This includes bearing size type (inner and outer race diameters), type, and configuration (single or double), as well as stud count and layout for secure fitting. Buyers can choose OE replacement to get more of the same performance or go with aftermarket parts for lower purchase prices and higher quality.