ASE T5 Suspension & Steering (Medium/Heavy Truck) cheat sheet

Integral steering gear adjustments are made in a fixed order: worm bearing preload first, then sector shaft mesh; mesh is set with the gear on center (the high point of the sector arc).

Measure free play at the steering wheel rim with the wheels straight ahead and the engine running; heavy-truck limits are commonly around 10-15 degrees of rim travel, but the OEM spec governs.

Low assist at idle plus whine and foam in the reservoir points to air in the system or a restricted pump inlet; bleed with the front wheels off the ground, lock to lock, keeping the reservoir full.

Relief pressure below spec at full lock indicates a worn pump or a leaking relief valve; normal relief pressure with no assist indicates internal leakage in the gear (piston seals or valve body).

A steering wheel that kicks or shimmies at road speed should be diagnosed first by checking tire and wheel radial/lateral runout, balance, wheel bearing play and kingpin play, not by replacing the gear.

Tapered tie-rod and drag-link studs must seat dry in a clean, undamaged taper; oil, grease or paint on the taper reduces friction and lets the joint work loose.

Wander or pull with acceptable alignment readings: inspect drag link and tie rod ends, kingpin bushings, frame cracks at the steering gear mounts, and steering shaft joints.

Use only the OEM-specified power steering fluid; mixing incompatible fluids causes seal swell, aeration, foaming and loss of assist.

Check ride height at the OEM-specified frame-to-axle reference points before judging spring sag; ride height sets driveline angles, caster and air-bag pressure.

Many truck spring U-bolts are torque-to-yield; replace rather than reuse them, and re-torque to specification after the first 100-500 miles because clamp load relaxes as parts seat.

A sheared leaf spring center bolt or a worn spring-eye bushing allows the axle to shift, producing dog tracking, spring-seat wear and rapid tire scrub.

Air ride height valve: adjust the link so the valve arm sits at the specified angle at design height; a bent or misadjusted link shifts load between bags and changes alignment angles.

Air bag inspection: surface cracks, chafing against brackets or oil contamination mean replacement; bags must never be operated below the OEM minimum pressure.

Worn torque rod (track bar) or walking-beam equalizer bushings show up as wander, constant steering correction and scuffed or feathered tire wear.

Shock absorber check: after a road test all shocks should feel similarly warm; a cold shock on one side is not valving and can cause tire cupping and porpoising.

Do not correct sagging springs with blocks or extra leaves beyond OEM design; exceeding GAWR overloads tires, brakes, wheel ends and axle housings.

Alignment sequence: set tire pressure and ride height first, then caster, then camber, and toe last, with the steering gear centered and the wheel held straight ahead.

Directional pull is toward the side with less positive caster or more positive camber; a side-to-side caster split is the most common cause of a steady pull on a level road.

Thrust angle is the angle between the vehicle geometric centerline and the perpendicular to the rear axle; a non-zero thrust angle makes the truck dog track and leaves the steering wheel off center.

Total toe is the sum of the left and right individual toe readings; adjust with the tie rod until total toe matches spec, then recenter the steering wheel.

Steering axis inclination is built into the knuckle and cannot be adjusted; SAI out of spec while camber reads correct indicates a bent steering knuckle or spindle.

Toe error produces feathered tread with sharp edges on one side of each rib; camber error produces a smooth wear pattern on one shoulder.

Turning angle (toe-out on turns) is checked on turn plates; an incorrect Ackermann curve from a bent steering arm causes tire scrub and squeal in tight turns.

On air-ride trucks alignment must be set at design ride height; raising or lowering ride height changes both caster and camber readings.

Match dual tire diameters within about 1/4 in (6 mm) when inflated; the larger tire carries more load while the smaller one drags and wears rapidly.

Wear diagnosis: center-only wear = overinflation; both shoulders = underinflation; one shoulder = camber; feathered ribs = toe; cupping = balance, shocks or wheel bearings; diagonal wear = misalignment or dual mismatch.

Torque wheel nuts with a calibrated wrench in a star pattern to OEM specification, and re-torque after the first 50-100 miles on a new or reinstalled wheel.

Loose wheel nut indicators: rust streaks radiating from the nut, shiny threads, cracked paint around the nut, or a polished stud.

Hub-piloted wheels use two-piece flange nuts and center on the hub; stud-piloted wheels use ball-seat nuts; the two systems and their hardware must never be mixed.

Inspect disc wheels for cracks between hand holes and around stud holes; cracked wheels are replaced, never welded, straightened or reamed.

Select inflation pressure from load/inflation tables for the actual measured axle load, not from the sidewall maximum; overinflation reduces traction and center-tread life.

Check radial and lateral runout with a dial indicator against OEM or TMC limits before balancing a vibration or shimmy complaint.

Fifth wheel adjustment: with the kingpin locked in the jaws, the jaws must close fully; check with the OEM gauge and adjust until there is no fore-aft slack.

Kingpin wear is measured with a kingpin gauge or micrometer at the worn area; replace the pin when diameter falls below the OEM limit, typically a few thousandths under 2.000 in.

Chucking, hard steering and accelerated kingpin wear commonly trace to a dry fifth wheel top plate; lubricate with OEM-approved grease at the specified interval.

Sliding fifth wheel: confirm both locking pins fully engage and the air cylinder holds them; partial engagement wears pin bores and can release under load.

Frame cracks typically start at crossmember gussets, bracket bolt holes and along the rail flange; stop-drill the crack ends and follow OEM repair procedures.

Check frame squareness with cross (X) measurements between matched reference points; an out-of-square frame causes dog tracking that alignment cannot correct.

Replace frame and fifth-wheel fasteners with the same grade as original, torque to spec, and mark each with a torque stripe for later inspection.

Cab air suspension ride height is set by the leveling valve link; a bent or misadjusted link causes continuous inflation or exhaust, cab lean and compressor cycling.

Locate cab air leaks with soap solution at bags, fittings, valves and lines; leaks let the cab sit unevenly and shorten compressor life.

Worn cab mount isolators or loose mount bolts cause clunks, cab shake and cracked brackets; inspect rubber for separation, crush and oil damage.

Cab shock absorbers control cab bounce and porpoising; a leaking or seized cab shock transfers vibration into the cab and accelerates isolator wear.

Before tilting the cab, secure loose items and confirm the latch releases fully; before working under a raised cab, install the safety prop.

Worn cab suspension bushings and pivot pins can feel like a steering wander complaint; check cab movement over bumps before diagnosing the steering system.