Hub assemblies go by many names in the heavy-duty industry. Hub Assembly. Wheel hub unit. Wheel hub bearing unit. No matter what you call it, the hub assembly plays an integral role in your wheel end system.
The hub assembly essentially enables your vehicle’s wheels to turn freely which is crucial for handling and safety. The exterior/tone ring is attached to or cast into your hub which is crucial for the proper operation of your anti-lock brakes (ABS) and traction control system (TCS) when equipped on your vehicle.
No matter if you are driving a semi-truck, pulling a commercial trailer, hauling debris on a construction site or working in the fields farming, you won’t go very far if your hub assembly isn’t working properly. In this article, we’ll break down the importance of your hub assembly. As we do, we’ll answer some of your top questions, which may include:
- What does the hub assembly do?
- What are the main components of a hub assembly?
- What causes wheel hub failure?
- What are the types of hubs to look for when buying?
- What are the best hub assembly brands?
How Does A Hub Assembly Work?
The hub assembly connects your application’s tires to your axle and houses the wheel bearings, that keep the wheels spinning freely. The assembly ensures a smooth ride for you and your load.
It’s positioned between the brake drums/discs and the axle.
- Outside the hub assembly: Your wheels are attached to the studs of the hub assembly.
- On the axle side: The hub assembly is slid onto a spindle, and inner and outer roller bearings are positioned between the axle hub and spindle, ensuring smooth rotation from the wheel to the axle.
- On the brake drum/disc side: attachment is determined whether you have disc brakes or drum brakes, and from there, inboard or outboard drums.
What Are The Main Components Of A Hub Assembly?
As you probably know or have figured out, the wheel hub consists of various, moving pieces when installed.
Inside the hub assembly
- Wheel Bearings – While there are many precision manufactured components that comprise the entire hub assembly, the vital wheel bearing is housed here. Brush up on your Wheel Bearing know-how by reading: Five Things You Need to Know about Wheel Bearings. This particular piece is critical to your truck’s performance: smoothness of the ride, to fuel efficiency, to the integrity of your brake and wheel end system. There are inner and outer bearings on either side of the hub.
- Seals: This part is responsible for keeping out contaminants like dirt, water, salt, debris, metal flakes and other tiny particles that wreak havoc on your bearings as well as containing the lubricants for the wheel end. Check out Wheelco’s Seals & Bearings Quick Guide to see what our team recommends if you need to replace yours.
- Lubrication: With moving parts, it’s important to reduce heat and friction. Depending on what type of application you are driving will determine the type of lubricant.
- Common heavy-duty vehicles use 75W-90 GL5 LS
- Severe applications commonly use Hi Temp EP 2 Red Grease
- Grease cap/dust cap: Pressed over the outer edge of the hub assembly, this component is used on the outside of the hub to keep debris out and lubrication in.
- O-Rings: In some models, O-rings are used as a last defense against grease/oil that may be leaking out of the hub assembly most commonly used with ConMet hub assemblies.
- Bearing snap ring: Some models use a metallic, rigid band keeps the roller bearing assembly in position during installation most commonly used with ConMet hub assemblies.
In oil bath applications, such as larger trailers, a bolt-on the cap is normally used.
Why Do Hub Assemblies Go Bad?
Just like any product, weather plays a major role in the longevity of your parts. Corrosion from the weather can wear down parts. Road treatment chemicals and salts also factor in for wheel hub corroding. Wheel hubs can be installed improperly and can be dangerous to driver safety. However, driving technique factors in as well as hitting potholes, curb checks and vehicle collisions can cause major damage to your hubs. Nevertheless, like any component, increasing frequency of use and wear and tear often mean you’ll need replacing the part sooner than later.
Common Signs and Symptoms Your Hub Assembly May Need Repairs or Replacement
Even though hub assemblies are typically low-maintenance parts, they do eventually wear down and need repairs and/or replacement.
- Roaring or grinding sound around the tires when you are moving is a symptom of a damaged wheel bearing. Contact a service technician as soon as possible.
- A clicking sound (often when you make turns) can be an indication that your hub assembly has some issues, which often means your bearings are damaged as well.
- A vibrating or loose steering wheel and gets worse as you accelerate. Drivers also report increasing vibration when making turns if their hub assembly needs replacing.
- Wheel wobbling can indicate a bent clamp or bearing.
- Pulling to one side when you push on your brakes is a common symptom that your brake pads have uneven wear or that your rotors are warped.
- Free play in the tire and/or wheel. If you are bringing your vehicle in to see a service technician at Wheelco or mechanic as recommended, (brake checks, oil changes, tire rotation, etc.) they will often inspect the status of your hubs and they may catch free play in the steering wheel before drivers notice.
- ABS sensor failure can occur if there is excessive play in your hub assembly.
- Overheating can indicate bearing failure, but it may also be overloading of frequent braking events.
Hubs Aren’t a “One Size Fits All”
If you’ve noticed any of the signs of symptoms that your hub assembly needs repair and/or replacement, we recommend having a Wheelco service technician inspect your hub assembly immediately. Likely, they will have a recommendation or diagnosis.
However, if you are confident in your service abilities, you’ll need to know that the type of hub you need depends greatly on what application or use it is for, bearing load and tire size. Class 6-8 semi will need a different hub for their drive axles as a medium-duty truck pulling a camper. At Wheelco, we stock many different types depending on your unique needs as well as brake drums, rotors and more if you need an overhaul.
Stud-piloted Hub vs. Hub-piloted Hub
What’s the difference between stud-piloted hubs vs. hub-piloted hubs? That’s a common question we get at Wheelco. So, let’s break this down.
The wheel bolt holes are flush on hub-piloted hubs. They require outer lug nuts to secure the wheel to the hub.
The hubs are designed with tangs to help center the wheel to the hub. The center hole of the wheel/hub bore fits over the matching size ridge on the hub. The lug nut will be flushed to the face of the wheel.
The wheel bolt holes are beveled/tapered for stud-piloted hubs. Dual wheel applications require inner and outer lug nuts to secure the wheel to the hub. Additionally, they need studs and ball-seat cap nuts for both the left and right side of the vehicle for proper installation. The lug nuts also have a matching taper edge. The centering of the lug nub in the tapered hole of the wheel forces the wheel to be centered on the hub.
Aluminum or Ductile Iron Hub Assemblies
When buying new hub assemblies, you’ll have the option of aluminum or ductile. Determining what is best for you, depends on your needs. Let’s review.
Aluminum Hub Assemblies
Aluminum hub assemblies are known for their precision-machined design. The aluminum alloy hubs weigh less, thus reducing your vehicles’ overall weight, increasing payload capacity and increasing fuel efficiency. If weight is a concern, we’d recommend using aluminum hub assemblies. Because of the design and material used, these hubs can be a more costly option.
Ductile Hub Assemblies
Ductile hub assemblies are dependable, usually require low maintenance and are strong. These hubs are easily cast, keeping costs down. And if weight isn’t your primary concern, we recommend this type of hub assembly.
PreSet vs. Conventional Hub Assemblies
If you are in the market for hub assemblies you have a few different options, depending on the brand, PreSet or Standard/Conventional and materials uses in assembly configurations. We’ll review some popular products on the market so you can get the best hub assembly for your specific needs.
PreSet/Pre-Adjusted Hub Assemblies
PreSet hubs are pre-assembled, pre-adjusted. Because of this innovative design, it cuts down install time, decreasing the likelihood of miscalibration and alignment upon installation. If you are looking for installation speed, reduce human error and do not want to invest in the tools needed to properly install a hub, you may choose a PreSet hub assembly. While this will reduce installation errors, purchasing this type of hub will still require regular proper torque and installation, maintains, and replacement over time.
Conventional Hub Assemblies
Conventional hubs require assembly. They do not come manufactured and assembled with bearings, seals, etc—although you can purchase these separately. Often we have drivers or service mechanics who choose this option if they only need to replace a component of the assembly, rather than the entire assembly itself.
At Wheelco, we recommend ConMet PreSet hubs that have many components including wheel seals, ABS equipped technology and bearings and more. We also stock standard hubs from Webb and Meritor. If you are looking to upgrade or replace your hub assemblies, we are ready to help you. Additionally, if you need installation, maintenance work and/or repair jobs, we can help. Simply give us a call or stop by one of our stores.