Steering, Brakes, and Suspension
Core concepts
Understand steering types: mechanical, hydrostatic (orbitrol), and articulated frame steering, plus steering cylinder and priority valve function. Brake content covers wet disc brakes, hydraulic and air systems, parking brakes, and brake adjustment. Suspension includes front axle suspension, cab suspension, and the role of accumulators and dampers. Know how steering and brake circuits share hydraulic supply via priority valves.
Traps
Questions often assume loss of engine power means loss of steering; hydrostatic steering with an orbitrol can retain manual steering capability, but braking and steering priority differ by design. Another trap is confusing wet disc brake wear with hydraulic failure. Air brake systems require correct adjustment and drain of moisture; do not overlook compressor and dryer faults.
Rule of thumb
Steering priority is usually highest in the hydraulic circuit; if steering is sluggish, check priority valve and pump flow before the steering unit. For wet brakes, drag or pull to one side often indicates a stuck piston or contaminated oil, not just worn discs.
Worked example
A tractor pulls to the right when braking. Inspect for a dragging right-side brake piston or unequal hydraulic pressure. If one side's wet disc pack is contaminated or a piston is stuck, that side may apply late or drag. Verify with a pressure test at each brake circuit and inspect oil condition before replacing discs.