The two drive axles have to agree with each other
Alignment on a tractor gets discussed as a front-axle matter, because that is where the steer tires are and the steer tires are what people notice. The drive axles are where a specific and expensive fault lives.
A tandem has two drive axles close together, and they are meant to point the same way. When they do not, each one is trying to steer the truck slightly differently, and since neither can win, the tires scrub against each other's direction for every mile the truck runs.
Nothing about that is audible from the cab. The truck goes where it is pointed. What it produces is drive tires wearing faster than they should across the whole set, which a fleet usually treats as the price of the work.
It also loads the front end, because the steer axle ends up correcting for what the drives are doing, which is how a drive axle problem turns up as a steer tire bill.
How to spot it before the rack
Compare drive tire mileage across units doing similar work. A truck whose drives consistently come off earlier than its stablemates, with no obvious reason, is the one to measure.
Wear that is even across each tire but fast across all of them points this way, rather than at the one-edge wear that suggests a toe or camber problem up front.
What gets measured
Steer axle angles, the alignment of each drive axle, and the relationship between them. Where the readings point at a worn or bent component rather than an adjustment, you get told.
The national heavy-duty truck alignment page covers the rest. Trailer alignment is offered here too, which matters when a combination still tracks badly with the tractor right.
About this store
The Jonesboro store runs seventeen services, carries all nine Purcell tire categories, and is managed by Tony Kuehnel.
See the national heavy-duty truck alignment page for all 40 locations.