Editing Axle (section)

==Full-floating vs semi-floating==
A full-floating axle carries the vehicle's weight on the axle casing, not the half-shafts; they serve only to transmit torque from the differential to the wheels. They "float" inside an assembly that carries the vehicle's weight. Thus the only stress it must endure is torque (not lateral bending force). Full-floating axle shafts are retained by a flange bolted to the [[Wheel#Hub|hub]], while the hub and bearings are retained on the spindle by a large nut.

In contrast, a semi-floating design carries the weight of the vehicle on the axle shaft itself; there is a single bearing at the end of the axle housing that carries the load from the axle and that the axle rotates through. To be "semi-floating" the axle shafts must be able to "float" in the housing, bearings and seals, and not subject to axial "thrust" and/or bearing preload. Needle bearings and separate lip seals are used in semi-floating axles with axle retained in the housing at their inner ends typically with [[Circlip|circlips]] which are 3¾-round hardened washers that slide into grooves machined at the inner end of the shafts and retained in/by recesses in the differential carrier side gears which are themselves retained by the differential pinion gear (or "spider gear") shaft. A true semi-floating axle assembly places no side loads on the axle housing tubes or axle shafts.

Axles that are pressed into ball or tapered roller bearings, which are in turn retained in the axle housings with flanges, bolts, and nuts do not "float" and place axial loads on the bearings, housings, and only a short section of the shaft itself, that also carries all radial loads.

The full-floating design is typically used in most ¾- and 1-ton light trucks, medium-duty trucks, and heavy-duty trucks. The overall assembly can carry more weight than a semi-floating or non-floating axle assembly because the hubs have two bearings riding on a fixed spindle. A full-floating axle can be identified by a protruding hub to which the axle shaft flange is bolted.

The semi-floating axle setup is commonly used on half-ton and lighter 4×4 trucks in the rear. This setup allows the axle shaft to be the means of propulsion, and also support the weight of the vehicle. The main difference between the full- and semi-floating axle setups is the number of bearings. The semi-floating axle features only one bearing, while the full-floating assembly has bearings on both the inside and outside of the wheel hub. The other difference is axle removal. To remove the semi-floating axle, the wheel must be removed first; if such an axle breaks, the wheel is most likely to come off the vehicle. The semi-floating design is found under most ½-ton and lighter trucks, as well as in SUVs and rear-wheel-drive passenger cars, usually being smaller or less expensive models.

A benefit of a full-floating axle is that even if an axle shaft (used to transmit torque or power) breaks, the wheel will not come off, preventing serious accidents.