The short version
- A hub assembly always contains the bearing, the hub flange and the seals. Those are the point of it.
- Wheel studs are usually pressed in already, but not always. Check the listing on trucks.
- The ABS sensor is the big variable. Many applications sell an ABS version and a non-ABS version of the same physical part.
- What is almost never in the box: the retaining clip, the axle nut, the dust shield and the rotor.
What is in a hub assembly matters because it arrives as one finished piece. No pressing, no preload to set, no seals to fit. Bolt it on and go.
That is mostly true, and it is why the industry moved this way. But “one finished piece” varies by brand and by application. The gaps are exactly the parts that stop the job at eight on a Sunday evening.
What is in a hub assembly every time
Every hub assembly worth the name contains three things, permanently and non-serviceably.
The bearing itself, pre-set at the factory. This is the part that matters most and the part you can least inspect. Preload was established on a machine under conditions no workshop can reproduce, which is precisely the benefit you are buying.
The hub flange, which is the machined face your wheel and brake rotor bolt against. Its flatness is not a detail. Runout here shows up as a brake pulsation that no amount of rotor work will cure, which is why manufacturers test for it specifically.
The seals, integrated rather than pressed in separately. On a serviceable bearing the seal is a part you fit and can get wrong. Here it is built in, and on many modern units the seal also carries the magnetic encoder ring the ABS system reads.
Timken lists what a hub unit is validated for before it ships. That covers flange runout, stud twist-off and push-out, seal durability, bearing life, and ABS sensor output. That list is a useful map of what actually fails on these parts in service.
Wheel studs: usually, not always
On the large majority of passenger car applications the studs arrive pressed into the flange, correctly seated and ready for the wheel.
The exceptions cluster on trucks and heavier applications. The same hub casting may be sold with different stud lengths or thread pitches, depending on trim, wheel type or whether the vehicle runs duals. Where that happens, the manufacturer sometimes ships the hub bare and lets you fit the studs the vehicle needs.
It is a quick thing to check and an annoying thing to discover late. If the listing does not say studs are included and the photograph shows a flange with empty holes, believe the photograph.
The ABS sensor is the real variable
This is where most returns come from, and the confusion is understandable because there are three different arrangements in circulation.
Sensor built into the hub
- Active sensor molded into the unit
- Wiring pigtail and connector attached
- New bearing means new sensor
- Costs more, fails as one item
Encoder ring only
- Magnetic ring in the seal face
- Sensor is separate, bolted to the knuckle
- You reuse your existing sensor
- Ring is fragile and directional
The third arrangement is a plain hub with no ABS provision at all, used on applications that never had wheel speed sensing at that corner.
The practical problem is that the ABS and non-ABS versions of a hub can be physically interchangeable. It will bolt up and it will hold the wheel on.
And the dash will light up, because nothing is reporting from that corner.
Whether a car had four wheel ABS often came down to trim level and model year, not the model itself. Timken’s listing for the 2007 to 2012 Hyundai Elantra splits on exactly this. One rear part number covers cars with four wheel ABS, another covers the non-ABS cars, and that is the same car in the same years.
If your hub has an encoder ring rather than a built-in sensor, handle it carefully. It is a magnetized surface on the seal, so a magnet can wipe it and a screwdriver can score it.
A damaged one produces an intermittent fault that is miserable to chase. There is more in how the speed sensor is integrated.
What is not in the box
Four things catch people out regularly.
- The retaining clip. On pressed-in applications a snap ring holds the bearing, and it has its own part number. Timken lists RET78 for a 2013 to 2015 Civic, RET188 for a Corolla, RET55 for an Elantra, and the old one usually deforms coming out.
- The axle nut. Many are single-use by design, either staked into a groove or fitted with a nylon locking insert that has already done its job once. Reusing a staked nut is a real failure path, not a technicality.
- The dust shield. The thin steel splash guard behind the rotor stays with the knuckle. If yours is rotted out, it is a separate part and worth doing while everything is apart.
- The brake rotor. Some heavily bundled kits include one. Most hub assemblies do not, and on captive rotor designs where the rotor sits behind the hub, this materially changes the job.
Sometimes you get a choice of how to buy it
Here is something worth checking before you order, because it can change both the price and the afternoon.
A 2003 to 2018 Corolla appears twice in Timken’s front listings. Once as bearing 510070 with clip RET188, which is the pressed-in repair. And once as HA590498, described as a front bearing and hub kit.
Same car, two routes. The bearing is cheaper to buy and much more expensive to fit. The kit costs more and may turn a press job into a bolt-on one.
Which is right depends on your tools, whether you are paying labor, and the state of the knuckle. If the old bearing has spun in its bore, the decision makes itself. That trade-off is worked through in choosing between the bearing and the whole hub.
One thing to do before you pull the old one
If your vehicle has a separate ABS sensor bolted into the knuckle, take it out before the hub comes off.
The sensor tip sits close to the hub. As the assembly comes away, especially if it needs a puller, the axle or the hub can knock it. The tip snaps off inside the knuckle bore, which turns a bearing job into a bearing job plus an extraction.
Two minutes with a small socket at the start avoids it. It is the most repeated advice on hub replacement threads, because people keep learning it the hard way.
Confirm front or rear, then left or right, since rears often differ. Confirm ABS or non-ABS for your trim. Add the retaining clip on a pressed-in application, and add an axle nut.
How to read the listing
Part listings are written for counter staff rather than for you, so a little translation helps.
| What it says | What it means |
|---|---|
| With ABS sensor | Sensor and pigtail attached to the unit. Reuse nothing. |
| With ABS ring, or tone ring | Encoder in the seal. Your existing sensor gets reused. |
| Non-ABS | No speed sensing at this corner. Wrong for an ABS car. |
| Bearing and hub kit | Complete assembly, usually bolt-on. |
| Repair kit | Ambiguous. Often bearing plus seal plus clip, no hub. |
| Clip, or RET number | The retaining ring, sold separately. |
If the listing is ambiguous, the photograph settles it faster than the description. A flange with studs is a hub assembly, a bare ring is a bearing, and a wiring pigtail means an integrated sensor.
The wider vocabulary problem is covered in the comparison of bearings and hub assemblies.
Common questions
What is in a hub assembly, and is the bearing included?
Yes, always. The bearing is pressed in at the factory and sealed. That is what makes it an assembly rather than a hub.
Do hub assemblies come with wheel studs?
Almost always on passenger cars, pressed in and ready. Some truck applications ship bare because stud length varies by configuration. Check the listing photograph.
Does it include the ABS sensor?
It depends on the design. Units with an integrated active sensor include it and a connector, while units with an encoder ring in the seal do not. Non-ABS versions have neither.
Do I need a new axle nut?
If the old one is staked or has a nylon insert, yes. Both are designed to hold once. They are inexpensive and it is not worth the risk.
Is the retaining clip part of what is in a hub assembly?
Rarely. On pressed-in applications it is a separate part number and it is worth adding to the order, since the original usually distorts during removal.
Does a hub assembly include the knuckle?
No. The knuckle is the casting that holds everything and connects to the suspension, and it is not a wearing part. Complete knuckle and hub units exist for some applications, sold as a different item at a higher price.