Face Spline Wheel Hubs Explained: What Every Technician Needs to Know
New Wheel Bearing Designs Can Change Installation Procedures
Some jobs are second nature to seasoned techs, like brake pads, filters, even hub replacements. But recent innovations in wheel hub design, like the face spline hub, are changing the game. If you’re not up to speed, a routine job could turn into a costly comeback.
Face Spline Wheel Hubs
An innovative wheel hub design that is coming to a bay near you is the Face Spline Wheel Hub, which can currently be found on multiple late model BMW and Mini vehicles. The face spline wheel hub design moves the axle splines from inner bore (inside diameter) of the wheel hub to the inner face of the wheel hub. This design has multiple advantages over a traditional splined Gen 3 wheel hub design, including 10% weight savings and the ability to transmit up to 50% more torque. With these advantages, it wouldn’t be surprising to see face spline wheel hubs being adopted by other OE manufacturers in the future, but this design changes more than just the wheel hub.
Hardware and Installation Differences
Because of the design of face spline wheel hubs, they do not use traditional hardware or wheel hub installation procedures. Since it is still a Gen 3 wheel hub, it has an integral mounting flange that secures the hub to the knuckle with mounting bolts, the same as traditional Gen 3 hubs. Face spline hubs then use an axle bolt that passes through the center of the wheel hub to secure the axle shaft and provide the clamping force that keeps the axle shaft splines securely mated with wheel hub splines.
Since the splines on the axle shaft mate vertically to the splines on the inner face of the wheel hub, it is critical to make sure the splines are properly aligned and mated before tightening the fastener to the proper torque spec. To do this, the drive shaft needs to be guided towards the inward face of the wheel hub until the splines are engaged. Then, the drive shaft must be held in place while the bolt is hand tightened.
To help keep the axle and hub splines engaged, the axle bolt is equipped with a compression spring that holds tension on the mating surfaces and keeps them aligned. The axle bolt will also have an o-ring which helps retain the spring prior to installation.
Once the axle bolt is secured, you can torque the bolt down to the proper torque spec. These face spline hubs also have a rolled closure design, which means the bearing preload is set to the proper spec from the factory, but using the proper torque spec on the axle bolt is still critical, even more so with the face spline hub design. In this design, the axle bolt serves not only to retain the axle shaft, but also to keep the wheel hub and axle shaft splines securely engaged. Failure to properly torque the axle bolt is asking for an expensive comeback, which could call for the replacement of the hub unit, and even the axle if the splines are damaged or stripped from improper engagement. If the splines come completely disengaged from each other, the vehicle will lose the ability to drive all together, and will produce some alarming noises, definitely not something a customer wants to experience.
And of course, it bears emphasizing, never use an impact wrench or other power tools to tighten or torque an axle bolt/nut. Hand tools and a properly calibrated torque wrench should always be used to properly install a wheel hub.
Other Differences
In addition to the aforementioned differences in the wheel hub, hardware and installation procedures, this design change also impacts the design of the axle. The axle will have a splined face to match the splines on wheel hub instead of the usual splined end. This shortens the overall length of the axle shaft, making it easier to separate from the wheel hub and disassemble, as well as facilitating an easier axle installation.
Ease of installation, weight savings and increased torque capacity are all advantages that are leading OE manufacturers to implement this spline face wheel hub design.
Keep an eye out for these face spline wheel hubs, and regardless of the type of wheel hub you are replacing, always follow OE procedures and use premium components—like BCA Bearings by NTN, engineered for precision and durability.