ASE H5 Suspension & Steering (Transit Bus) cheat sheet

Road feel and steering effort complaints are classified as hard steering, wander, shimmy, pull, or excessive free play; each has a distinct diagnostic path.

Excessive steering wheel free play is measured at the rim with the wheels straight ahead and the engine running on power-assisted systems; spec is typically 10-30 mm (0.4-1.2 in) depending on gear type.

Hydraulic power steering pump flow is typically 2-4 gpm at relief pressure of 1,000-1,500 psi; low flow at idle causes hard steering at low engine speed.

A steering gear with a worn recirculating-ball nut or sector shaft shows free play that does not reduce when the lash adjuster is set per procedure.

Shimmy at a specific road speed usually indicates wheel/tire imbalance or runout, not a steering gear fault; shimmy at all speeds points to worn linkage or gear.

Steering pull that follows road crown is normal; pull on a flat, level surface indicates alignment, tire conicity, or a dragging brake.

Power steering fluid contaminated with metal or burnt smell indicates pump or gear failure; flush is required before replacing a component.

Variable-assist and electronic power steering systems set fault codes when torque sensor or motor current is out of range; scan tool data confirms before parts replacement.

Tilt and telescoping column mechanisms use a locking pawl or clamp; looseness in the tilt pivot is a common cause of steering wheel vertical free play.

The steering shaft uses collapsible or slip-joint sections designed to absorb impact energy; a collapsed section must be replaced, not straightened.

Tie rod ends are checked for axial and radial play with the wheels loaded; any detectable play at the ball stud requires replacement.

Drag link and tie rod adjusting sleeves have opposite-hand threads; count turns during adjustment so the toe setting is not lost.

Idler arm and pitman arm play is measured at the joint; idler arm bushing wear causes wander and uneven tire wear on the front axle.

Power steering hose restrictions cause whine and hard steering; a pressure and return flow test isolates a collapsed hose from a failing pump.

The steering gear must be centered (high point) before setting toe; off-center gear causes unequal turning radius and premature gear wear.

Power steering fluid level is checked with the engine off and the system at operating temperature; aerated fluid indicates a suction-side air leak.

Independent front suspension uses control arms with ball joints; ball joint axial play limit is typically 0.5 mm (0.020 in) for a loaded joint.

Torsion bar ride height is set by the anchor arm adjusting bolt; changing ride height changes camber and toe on SLA suspensions.

Coil spring sag is diagnosed by comparing curb height to specification at the specified measuring points, not by visual inspection alone.

Worn control arm bushings cause wander, uneven camber, and clunking over bumps; check for cracking and separation at the bushing.

Air suspension front bags leak at the top seal or airline fitting; soap solution testing locates leaks that a static height check misses.

Shock absorber condition is evaluated by bounce test and by inspecting for fluid leakage; a leaking shock is replaced in axle pairs.

Kingpin inclination and included angle are non-adjustable; a bent spindle or knuckle changes these angles and requires component replacement.

Sway bar link and bushing wear produces a rattle over bumps and body roll increase; check links with the suspension at ride height.

Rear axle lateral location is controlled by a track bar or Panhard rod on coil-spring rear suspensions; worn bushings cause body shift and dog-tracking.

Leaf spring condition is assessed by checking for broken leaves, center bolt shear, and shackle bushing wear; broken leaves change ride height and pinion angle.

Air suspension rear ride height is maintained by height sensors; a faulty sensor causes the system to over-inflate or not inflate.

Rear wheel bearing play is checked by rocking the wheel at 12 and 6 o'clock with the brake applied to isolate bearing from brake noise.

Pinion angle changes with ride height; incorrect pinion angle causes driveline vibration that is often misdiagnosed as a tire or wheel problem.

Rear shock absorber mounting points and bushings are inspected for cracks; loose upper mounts cause a clunk over bumps.

A rear axle that is not centered causes dog-tracking and accelerated tire wear; measure from frame rail to axle on both sides.

Rear suspension air bag replacement requires deflating the system and supporting the axle; never work under an air-suspended vehicle without stands.

Camber is the inward or outward tilt of the wheel viewed from the front; positive camber tilts the top outward, negative tilts inward.

Caster is the forward or rearward tilt of the steering axis; positive caster improves straight-line stability and increases steering effort.

Toe is the difference in distance between the front and rear of the tires at hub height; toe-in means the fronts are closer together.

Thrust angle is the angle between the vehicle centerline and the rear axle; a non-zero thrust angle causes the steering wheel to be off-center.

Included angle is camber plus SAI; it is not adjustable and a value out of spec indicates a bent spindle or knuckle.

Set toe last after camber and caster, and center the steering wheel before locking the wheel; toe change affects the steering wheel position.

Alignment specifications are given as a range with a preferred value; adjust to the preferred value, not the edge of the range.

Ride height must be checked before alignment; sagging springs or incorrect tire pressure change camber and toe readings.

Tire placard pressure is the cold inflation pressure for the vehicle; never use the maximum pressure molded on the sidewall as the operating pressure.

Tread depth is measured in the major grooves; the legal minimum is 1.6 mm (2/32 in), and replacement is recommended at 3 mm (4/32 in).

Radial and lateral runout limits are typically 1.0-1.5 mm (0.040-0.060 in); excessive runout causes vibration that balancing cannot correct.

Wheel balance is corrected with static (single-plane) and dynamic (two-plane) weights; a dynamic imbalance causes shimmy and wheel hop.

Lug nut torque is applied in a star pattern to the manufacturer's specification; overtightening warps rotors and distorts wheels.

Tire conicity causes a steady pull that changes direction when tires are rotated side to side; it is a tire manufacturing characteristic.

Load range and speed rating must meet or exceed the original equipment specification when replacing tires on a transit bus.

A wheel with a bent rim shows runout at the bead seat; replace the wheel rather than attempting to straighten it.