Lift axles are non-powered and are installed ahead of or behind the driving tandem axles on a straight truck or tractor. If it’s ahead of the tandem, a lift axle is called a “pusher.” If it’s behind, it’s a “tag.” Such axles can also be installed ahead of or behind a trailer’s tandem.
Lift axle suspensions use air bags to carry weight, and either air bags or steel springs to raise the axle when it’s not needed. If two sets of air bags are used, one set is inflated while the other is deflated. If steel springs raise the axle, the weight-bearing air bags must first be deflated to allow the springs to retract the axle. All this is controlled by the driver, using electric switches or air valves close at hand.
Like all other parts on a commercial motor vehicle, lift axles are bound to fail. The quickest way to get help fast is to have a semi-truck roadside assistance coverage plan. They can provide a tow to the nearest repair shop and get you back on the road quickly. The best way to prevent a lift axle failure is to check the air pressure in your bags regularly – the bags should be set to about 30 psi – and keep routine maintenance up on your vehicles.