ASE S5 Suspension & Steering (School Bus) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Steering ratio definition

The number of steering wheel degrees required to turn the road wheels one degree. A higher ratio means less effort and slower response; a lower ratio means quicker response and more effort.

Recirculating ball gear

A steering gear in which a worm gear drives a ball nut through circulating steel balls. It reduces friction and multiplies torque, allowing low steering effort with high durability.

Rack and pinion

A steering system where a pinion gear on the steering shaft meshes with a toothed rack. One pinion rotation moves the rack a fixed linear distance, producing direct steering response.

Center gear lash adjustment

Steering gear lash must be adjusted only with the gear at the straight-ahead center position. Adjusting off-center preloads the gear and causes binding near the ends of travel.

Idler arm play check

With the wheels straight and suspension loaded, rock the road wheel while holding the steering wheel. Perceptible up-down movement at the idler arm indicates worn bushings.

Collapsible steering column

A column designed to collapse or slip on impact, absorbing energy instead of transmitting it to the driver. Mesh or slip-joint designs are common on school buses.

Pitman arm indexing

The pitman arm is splined and must be installed with the steering gear at center and timing marks aligned. Incorrect indexing leaves the steering wheel off-center.

Universal joint phasing

On a two-joint steering shaft, yokes must be phased so joint angles cancel velocity fluctuation. Misphasing causes binding and uneven steering feel through rotation.

Horn wire in column

A horn that sounds while turning usually indicates a chafed or grounded horn wire or slip ring inside the steering column, not a failed horn relay.

Tilt column lock pawl

A tilt column uses a spring-loaded pawl engaging a toothed plate. Popping or looseness under load indicates a worn pawl, spring, or shear pin.

Power steering relief valve

A valve in the power steering pump that bypasses excess flow at full lock, limiting maximum pressure to protect hoses, seals, and the gear from damage.

Bleeding hydraulic steering

Air in the system causes whine, foam, and jerky assist. Bleed by cycling the steering lock-to-lock with the engine off, then running, keeping the reservoir full.

Electric power steering

An EPS system uses an electric motor to assist at the column, pinion, or rack. The module varies assist using steering angle, torque sensor, and vehicle speed inputs.

Spool valve imbalance

A binding or miscentered spool valve in the steering gear produces unequal assist left versus right. Compare effort in both directions at equal engine speed to isolate it.

Power steering fluid match

Using the wrong power steering fluid can swell seals and alter viscosity. Always match the OEM specification, such as automatic transmission fluid or a dedicated power steering fluid.

MacPherson strut

A suspension unit combining spring and shock absorber into one assembly that also locates the wheel. The upper mount carries both spring and damping loads.

Ball joint play check

Load the ball joint with the vehicle weight or a jack under the lower arm, then measure axial and radial play. Compare to specification before condemning the joint.

Sway bar function

A stabilizer bar links opposite sides of the suspension to reduce body roll. A broken link or worn bushing increases roll and causes a rattle over bumps.

Strut rod purpose

A tension or compression rod controls fore-aft wheel location. Worn bushings cause braking pull and clunking during acceleration and braking.

Strut camber adjustment

On many strut suspensions, camber is set with an eccentric bolt at the strut-to-knuckle joint or by slotting the strut tower per the OEM procedure.

Leaf spring main leaf

The main leaf locates the axle and carries the load; additional leaves increase rate and capacity. Shackles allow the spring to lengthen as it flattens.

Track bar function

A panhard or track bar controls lateral axle location in a trailing-arm rear suspension. Worn bushings allow rear steer and dog-tracking.

Rear height control valve

A valve that senses ride height through a linkage and adds or exhausts air to maintain design height. A leak causes sag and continuous compressor cycling.

U-bolt re-torque

U-bolts clamp the axle to the leaf spring and must be re-torqued to specification after spring or axle work. Uneven torque can shift axle alignment.

Camber definition

The inward or outward tilt of the wheel top from vertical. Positive camber tilts the top outward; negative tilts it inward. Excessive camber causes one-sided tire wear.

Caster definition

The forward or rearward tilt of the steering axis. Positive caster improves straight-line stability and returnability but increases steering effort when excessive.

Toe definition

The difference in distance between the fronts and rears of the tires. Toe-in means the fronts are closer together; toe is the primary cause of feathered tire wear.

Thrust angle

The bisector of rear total toe. Unequal rear toe produces a nonzero thrust angle, causing dog-tracking; rear alignment must be corrected before the front.

Included angle

The sum of camber and steering axis inclination. Comparing included angle side-to-side helps detect a bent spindle, knuckle, or strut.

Tire size decoding

In P235/75R15, 235 is section width in millimeters, 75 is the aspect ratio, R means radial construction, and 15 is rim diameter in inches.

Wheel bearing preload

Tapered roller wheel bearings require a specified preload or end play. Over-tightening causes heat and premature failure; under-tightening causes play and wobble.

Tire wear diagnosis

Center wear indicates overinflation; both edges indicate underinflation; one edge indicates camber; feathered edges indicate toe; cupping indicates shock or balance problems.