Full-Floating Vs. Semi-Floating And Other Axle Queries
There are several basic axle varieties used in 4WDs, and each has some specific design pros and cons. There are front steering axles and rear fixed axles. Axle designs can vary in load handling, bearing and flange type, and gear set configuration. In this article, we'll take a look at the various axles and discuss the benefits of the designs.
Semi-Floating vs. Full-Floating
There are two types of rear axles found on light-duty 4WDs: Semi-floating and full-floating. Each has its advantages and disadvantages.
A semi-floating axle is very common on the rear of most 4WDs. It consists of an axle shaft on each side that is splined on the inner end where it mates to the differential and has a wheel flange where the wheel studs mount at the other end. This assembly typically mates to the end of the axle housing using some type of bolted flange arrangement. The axle shaft also rides on a large roller or ball bearing out at the end of the axle housing.
For a full-floating system, the axle shaft only serves to transmit the rotational torque from the differential out to the wheel. It does not carry the weight of the vehicle as a semi-floater does. On a full floater, a spindle is attached to the outer end of the axle housing. The wheel hub is mounted on this spindle and rides on tapered roller bearings. It is this assembly that carries the vehicle weight. As such, a full-floating axle system is considerably stronger than an equivalently sized semi-floating system.
For those of you who carry heavy loads, this means your axle load capacity is greatly increased with a full-floater. Load ratings for similar vehicles with the two different axles are usually significantly different. If you do hardcore wheeling on big tires, a full-floater means that your axle shafts can also handle much more loading than a similar semi-floater because it now must only handle torque loading.
Further advantages of a full-floater include being able to remove a broken axle shaft while keeping a functional rolling tire on that corner of the vehicle. This can be done since the wheel actually bolts to the wheel hub that rides on the spindle attached to the axle housing. If the axle has been fitted with manual locking hubs, it may be possible to unlock the rear hubs for towing a disabled vehicle on the trail or for flat towing over the road.
It is also possible to convert some semi-floating rear axles to full-floating configuration using aftermarket kits. These kits allow an owner to easily upgrade the axle shaft strength of his axle. However, such a kit does not upgrade the differential assembly so axles having this portion as a weak link to begin with would not benefit much from such a conversion.