A wheel loader was brought in because it was violently eating the outer edges of its front tires. The operator was replacing a set of $4,000 solid rubber tires every three months due to extreme tread scrub. The shop had performed a front-end alignment on the axle twice, but the tires kept peeling off.
We watched the machine drive across the lot. It was "dog-tracking"-the rear frame was offset to the left of the front frame by nearly four inches. The loader looked like it was crabs walking down the road. The front tires were fighting the rear tires for directional dominance, and the front tires were losing, scrubbing rubber constantly.
We jacked the center of the machine up and inspected the articulation joint. The main center pin, which connects the front and rear frames, was held in place by massive top and bottom bushings. We grabbed the rear frame and pried it with a heavy bar. The rear frame rocked independently of the front frame by over an eighth of an inch. The center pin bushings were completely worn out.
Every time the operator pushed into a dirt pile, the rear frame twisted on the worn center pin, forcing the front frame to skew slightly to the side. The harder the operator pushed, the more the machine twisted, and the more the front tires scrubbed. The front-end alignment was perfect, but the center joint alignment was destroyed. We replaced the center pin and the oversized bimetallic bushings, and the machine tracked arrow-straight, saving thousands in tire costs. If your loader is eating front tires and the front axle alignment is perfect, always check the center pin for play.
