The short version
- Serviceable vs sealed is the single distinction that decides everything else about a bearing.
- Serviceable means loose tapered bearings you clean, repack and adjust. Sealed means a unit you replace.
- Trailers stayed serviceable because they are cheap, low speed and get submerged.
- Cars went sealed because a factory fill beats a hand pack, not because it lasts longer in theory.
Almost every disagreement about wheel bearings comes down to two people describing different designs. Serviceable vs sealed is the line. Once you know which side you are on, most of the advice sorts itself out.
It also explains why trailer guidance and car guidance contradict each other so often.
What serviceable vs sealed actually describes
| Aspect | Serviceable | Sealed |
|---|---|---|
| Construction | Two loose tapered bearings and races | One closed cartridge or hub unit |
| Grease | Packed by hand | Filled at the factory |
| Clearance | Set by you, as end play | Set internally, as preload |
| The nut | Adjusts the bearing | Clamps the assembly |
| Maintenance | Repack on an interval | None possible |
Look at the fourth row. The axle nut does completely opposite jobs on the two designs. A torque figure from one destroys the other.
That is on the torque specs page.
Why trailers kept the serviceable design
A trailer hub is a simple spindle with two tapered bearings. The whole assembly costs less than a car hub unit.
Boat trailers get dunked, which no sealed unit tolerates for long. Being able to open it up and inspect is genuinely valuable.
The service itself is on the repacking page, and the trailer specifics are on the trailer page.
Why cars went sealed
A hand packed bearing is only as good as the person packing it. The bench cleanliness and the adjustment afterwards matter too.
A factory sealed unit has a measured fill and no contamination on assembly. Its preload cannot be set wrong.
Averaged over millions of cars that never saw a repack, sealed wins comfortably. That is a statement about the fleet rather than about any one well maintained vehicle.
What the phrase promises is on the sealed for life page.
Telling which you have
A removable cap over a castellated or adjustable nut, with a cotter pin or a lock washer, means serviceable.
A large one piece flange with a single big nut means sealed. So do four bolts through the back of the knuckle.
The cap itself is on the dust cap page. The wider identification is on the bearing vs hub page.
Which rules apply to you
Repacking, adjusting end play, checking a service interval and reading the old grease all apply to serviceable bearings only.
Replacing on condition, never opening the unit and ignoring mileage entirely all apply to sealed ones.
Most bad advice online is correct guidance applied to the wrong design.
Where both exist on one vehicle
- Check each corner separately, since a vehicle can mix the two.
- Expect serviceable at the rear on older rear drive cars and light trucks.
- Expect sealed at the front on anything front wheel drive.
- Check a 4×4 front, which may be serviceable behind locking hubs.
- Apply the matching rules to each corner rather than to the car.
The locking hub case is on the locking hubs page.
This distinction is also what decides the number of bearings on your car, which is four or eight depending on the design.
Common questions
What is the difference in serviceable vs sealed wheel bearings?
Serviceable bearings are loose tapered sets you repack and adjust. Sealed units are closed at the factory and replaced whole.
Which lasts longer?
A well maintained serviceable set can last indefinitely. Across a whole fleet, sealed units last longer because they remove human error.
Why do trailers still use serviceable bearings?
They are cheap, they run slowly, and boat trailers get submerged. Being able to open and inspect is worth more there.
Can I tell which I have without tools?
Usually. A removable dust cap over an adjustable nut means serviceable. A large flange with one big nut means sealed.
Does the axle nut do the same job on both?
No, and this is the important part. On a serviceable set it sets clearance, and on a sealed unit it clamps the assembly.
Can one car have both?
Frequently. Sealed at the front and serviceable at the rear is common on older rear drive cars and light trucks.
Why does online advice contradict itself so much?
Because most of it is correct guidance for one design being applied to the other.