Steering Columns, Linkages, and Power Steering Components
The steering column on a transit bus carries more than steering input: it often carries the tilt/telescope mechanism, horn circuit, turn signal and wiper switches, and sometimes the ignition interlock. Diagnose column complaints by isolating whether the bind or noise is in the column itself, the intermediate shaft, or the gear. A classic trap is a binding upper bearing or misadjusted tilt mechanism that mimics a failing power steering pump because the driver reports 'hard steering.'
On linkages, understand the geometry: drag link, tie rod, and pitman arm transmit motion while the idler arm supports the far end of the linkage. Worn tie rod ends cause toe change and wander; a worn idler arm causes excessive vertical free play and wander that is worse on rough roads. Test linkage play with the wheels straight ahead and the steering wheel loaded slightly, watching each joint for lost motion.
Power steering components
Know the function of the pump, reservoir, relief valve, flow control valve, and cooler. The flow control valve limits maximum flow; the relief valve caps maximum pressure. A sticking flow control valve can cause heavy steering at low rpm or a sudden loss of assist.
Worked example
Driver reports a clunk and slight wander over bumps. With the wheels straight and an assistant rocking the wheel, you observe vertical movement at the idler arm pivot but no movement at the tie rod ends. Replace the idler arm assembly and recheck toe, since idler wear changes effective toe under load.