The wheel driver is splined both internally and externally, to transmit drive from the axle half-shaft to the hub. The nature of the fit between the driver splines and the half shaft and hub is important for satisfactory operation of the assembly.
There should be a minimum clearance between the half shaft and the driver, but the driver must be able to slide freely on the half shaft. As manufactured, the splines on the shaft will not have a sharp corner in the root of the spline, whereas the driver is likely to have a sharp corner in the corresponding position. If fitting a new driver to a new or relatively new shaft it will be necessary to remove the sharp corner on the wheel driver splines to ensure that there is no interference between the two.
The wheel driver should be a light tap fit in the hub. When in position it should enter the hub as far as it will go, when it will butt up against a shoulder at the inner end of the hub splines. In this position there will be a short length of hub spline at the outer end of the spline which is not in contact with the driver spline. Over time there is relative movement between the wheel driver and the hub, which generates wear in the splines where they are in contact. However, the short length of spline in the hub that is not in contact with the driver does not wear. This is significant when considering the alternatives to overcome wear between the hub and driver – see below.
The wear between the wheel driver and the hub gives rise to free play in the transmission, and the time will come when this results in knocks coming from the rear hubs particularly when transitioning from forward to reverse and back again, or when starting to move from stationary. When this occurs it may be appropriate to fit an oversize wheel driver with external splines being wider than standard to take up the wear. Before a suitable oversize driver is specified the following must be taken into account:
1 . Originally the hub and wheel driver splines were straight-sided and square in cross-section and contacted over the full width of the spline. As the splines in the hub and driver wear, both will wear unevenly and will no longer be straight-sided although they will make good contact, whereas the new oversize driver will have square and straight-sided splines. When in position in a worn hub the new driver will not contact the hub over the full width of the spline, the drive being transmitted through a very small area of contact. Consequently, initial wear will be rapid as the driver beds into the hub, resulting in the return of free play between the hub and driver.
2 . When fitting an oversize driver, it has to pass through the unworn length of spline at the outer end of the spline in the hub; this will only accept the size of driver originally fitted. A new driver of this size can be fitted but once in its working position it will be engaging with worn splines in the hub and free play will be only partially eliminated.
To overcome the problems of fitting a new driver to a worn hub either
- the worn splines within the hub need to be re-machined straight and true, and a driver specified to suit the refurbished hub, or
- a new hub and standard driver should be fitted.
Wear can occur between the central splines on the wheel driver and the splines on the halfshaft; usually this is much less significant than that between the driver and the hub. If the halfshaft is worn it will need to be replaced.