A quarry operator reported that a Volvo A25G 25-ton articulated hauler had developed a progressive rear-axle fault over a four-month period. When the hauler was loaded and traveling across the quarry's rough haul road, the rear bogie axle would vibrate noticeably, and the rear frame would wobble laterally as the machine traversed uneven ground. The rear tires showed uneven wear concentrated on their inner edges, and the operator reported that steering precision during reverse travel had degraded - requiring more correction to keep the hauler tracking on the intended path. The machine also produced a faint rhythmic "clunking" from the rear bogie assembly whenever it traversed a bump at speed.
The technician first understood the A25G's rear-suspension architecture. The hauler's rear bogie axle is suspended on a "straddle-mounted bogie beam" - a heavy steel beam that spans the rear frame and connects to each rear wheel assembly through a "Bogie Axle Pin" supported on "Bogie Pin Bushings." The bogie beam allows each rear wheel to move independently as the machine traverses uneven ground, maintaining tire contact and distributing load across both wheels. The "3-point mounting system" isolates the bogie beam from the rear frame's shock loads. When the bogie pins or bushings wear, the rear axle develops lateral play - producing the vibration, wobble, and steering imprecision the operator described.
He verified the symptom by measuring the bogie assembly's play with a dial indicator. Positioning the indicator against the bogie beam's outer edge and applying lateral force with a pry bar, he measured total lateral play of approximately 6 millimeters - far beyond the 1-millimeter allowable limit, confirming significant wear in the bogie's pin-and-bushing assembly. He then inspected each "Bogie Pin Bushing" - the hardened steel bushings that sit between the bogie pins and the bogie beam's mounting eyes. The bushings showed visible wear, with the inner surfaces worn into oval profiles and the clearance between pin and bushing visibly greater than specification. The "Bogie Pins" themselves showed corresponding wear - the pins' surfaces had worn into matching oval profiles at the points of maximum contact with the bushings. He further inspected the bogie beam's mounting bearing - the large bearing that allows the beam to oscillate relative to the rear frame - and found it dry and contaminated, indicating the bogie beam's grease points had not received regular lubrication.
The root cause was traced to bushing wear compounded by neglected lubrication. Bogie pin bushings are subjected to continuous shock loads every time the hauler traverses uneven haul road, and they rely on regular grease application to maintain a lubricating film between the pin and the bushing's inner surface. The hauler's service history showed the bogie grease points had not been serviced at the manufacturer's specified intervals - likely due to the grease points being positioned in hard-to-access locations that required the machine to be positioned on a service pit. Over extended service, the lack of lubrication had accelerated bushing wear, and the worn bushings had then allowed the bogie pins to rock under load, further accelerating both the pin and bushing wear.
The repair involved replacing all four bogie pin bushings with new units, replacing both bogie pins with new pins (the worn pin surfaces were beyond acceptable limits), and replacing the bogie beam's mounting bearing with a new unit. All components were lubricated to Volvo's specification during reassembly, and the bogie assembly's grease points were marked for inclusion in the machine's preventive maintenance schedule. After reassembly, the dial-indicator measurement of the bogie assembly's lateral play was reduced to under 0.5 millimeters - within specification. A loaded haul-road test showed the vibration eliminated, the rear frame tracking stable across uneven ground, and the rhythmic "clunking" gone. Steering precision during reverse travel was restored, and rear-tire wear patterns were expected to normalize over subsequent operation. Bogie grease-point service was added to the hauler's 250-hour maintenance checklist, with the machine positioned on a service pit during each service interval to ensure full access to all grease points.
