A limestone quarry reported that a SEM 660D wheel loader's steering would drift (turn slowly) when driving straight, and the steering wheel would "chatter" (vibrate) when turning at full lock.
The technician first checked the "Steering Priority Valve" and "Orbitrol," which were functioning. He then inspected the "Steering Cylinders" (located on the rear frame). He found the "Rod Eye Bushing" (the pivot point connecting the cylinder to the frame) was severely worn, with a 3mm gap.
This gap allowed the cylinder to "bounce." When the machine hit a bump, the cylinder rod would extend slightly due to the clearance, causing the wheels to turn (drift). The "Chatter" was caused by "Air in the Pilot Line." He traced the pilot line from the steering wheel to the priority valve. The "Banjo Bolt" fitting at the priority valve was loose. The loose fitting allowed air to be sucked into the system when the steering wheel was stationary.
The repair involved replacing the "Rod Eye Bushing" and "Pivot Pin." The cylinder rod was re-bushed to restore the tight tolerance. The loose banjo bolt was tightened, and the steering system was purged of air by cycling the steering wheel 10 times with the engine at low idle. The steering became firm and precise, eliminating the drift and chatter.
