The short version
- Four things on this job have a right way round, and none of them announce it.
- The encoder face is the expensive one. Backwards means an ABS light from the first mile.
- A seal lip points at what it keeps out. That single rule covers most seals.
- Photograph everything before it comes apart. It takes ten seconds and it answers all of this.
Getting wheel bearing orientation right matters more than it looks like it should, because most of these parts fit either way round.
They just do not work either way round.
The one that costs money
Many modern hubs read wheel speed from a magnetized ring built into one of the seals. It looks like plain black rubber.
Fitted backwards, the magnetized face points away from the sensor and the system reads nothing. The warning light appears immediately.
The bearing is not damaged, but it has to come out again, and on a pressed design that usually means it is finished.
Identifying which side carries the encoder is not always obvious, and the tell is usually magnetic rather than visual.
A steel feeler gauge or a paperclip is attracted to the encoder face and not to the plain one. That is the cheapest test available.
How the encoder works and what else damages it is on the ABS sensor page.
Seals, and the rule that covers them
A seal has an asymmetric lip. One face has a spring behind it and a defined lip angle, the other is usually flat.
A grease seal points its lip inward, toward the grease it is retaining. A dirt exclusion seal points outward, toward the road.
Most wheel bearing seals are doing both, and the garter spring side faces the grease.
Fitted backwards, a seal does not fail dramatically. It just leaks slowly and lets water in, which is the way most bearings actually die.
Why that matters so much is on the seals page.
Tapered cones and cups
On a serviceable hub the tapered parts also have a direction, and it is set by the geometry rather than by a marking.
The two cones face opposite ways, angled so that between them they resist sideways load in both directions. That opposition is the entire design.
Fit one the wrong way and the pair cannot be adjusted to any useful clearance. It will feel wrong immediately.
Why the opposing angle exists at all is on the bearing types page.
Snap rings
Stamped retaining rings have a sharp edge and a rounded edge, and the sharp one goes toward the load.
The difference is small enough to miss and detectable with a fingernail. Details are on the snap ring page.
The habit that solves all of it
Take pictures of each part in place, from a couple of angles, before it comes off. Include the sensor lead routing and every clip.
Phone photos cost nothing and they answer questions you did not know you would have, three hours later with the car apart.
Marking is the other half. A paint pen line across a joint before separating it records the relationship precisely.
Things that look directional and are not
Worth knowing, so you do not lose an hour to a wheel bearing orientation decision that does not exist.
A plain sealed hub unit generally cannot be fitted backwards, because the flange and bolt pattern only go one way.
Plain double row bearings with no encoder are often symmetrical, and either face works.
The dust cap has an obvious inside and outside and no subtlety to it.
If a paperclip sticks to one seal face and not the other, that bearing has an encoder and it is directional.
If neither face attracts, orientation is far less critical, though the seal lip rule still applies.
If you already fitted it backwards
The consequence of getting wheel bearing orientation wrong depends entirely on which part.
An encoder backwards throws a light immediately, so you will know before you drive far. The bearing comes out and, on a pressed design, is usually scrap.
A seal backwards gives no immediate sign at all. It shows up as grease loss or an early failure months later.
A tapered cone backwards reveals itself during adjustment, because no setting feels right.
What removal does to a bearing that has been fitted once is on the single use parts page.
Common questions
Does wheel bearing orientation matter?
On several parts, yes. The encoder face, the seal lip, tapered cones and snap rings all have a correct direction.
Which way does the encoder face?
Toward the ABS sensor. Fitted backwards it reads nothing and the warning light appears on the first drive.
How do I tell which side has the encoder?
Hold a paperclip or steel feeler gauge near each face. The encoder side attracts it and the plain side does not.
Which way does a wheel bearing seal go in?
Lip toward what it is sealing against, with the garter spring facing the grease. Backwards it leaks slowly rather than failing outright.
What happens if a seal goes in backwards?
Nothing obvious at first. It lets water in gradually, which is how most wheel bearings actually fail.
How do I avoid getting any of it wrong?
Photograph every part in place before removal, from two angles, including the sensor lead routing and clips.
Are all bearings directional?
No. Plain double row bearings without an encoder are often symmetrical, and bolt-on hub units only mount one way.