An inter-axle differential assembly includes a forward side gear and a rear side gear that are supported by an input shaft. The forward and rear side gears are in meshing engagement with a plurality of inter-axle differential pinion gears that are supported on a spider. The spider is driven by the input shaft and has a plurality of legs with each leg supporting one of the plurality of inter-axle differential pinion gears. A helical drive gear is fixed for rotation with the forward side gear. The helical drive gear includes a center cavity defined by a spherical inner surface. The spider and the plurality of inter-axle differential pinion gears are positioned within the center cavity. This eliminates the need for an inter-axle differential housing assembly and reduces standout.