S5 School Bus — Suspension & Steering — practice test

High-yield S5 topics

The material that shows up year after year. If you're short on time, start here.

• Steering wheel lash and where it really comes from. Know the FMCSA 393.209 table cold: a 20 in. wheel is out of service past 2 1/2 in. of lash on manual steering but 5 1/4 in. on power. Then know that on a conventional bus the lash is usually NOT the gear - it is the intermediate shaft U-joints, the slip spline, a loose pitman arm, or a worn drag link socket. Isolate it by having a helper rock the wheel while you watch each joint.
• Integral gear hydraulics: pressure test, flow test, and the poppets. Inline gauge with a shutoff valve between pump and gear, engine at idle, close the valve for no more than about 5 seconds at a time or you cook the fluid. Full-lock pressure is poppet-limited, not relief pressure - that is the whole point of the poppets. Set the axle stops FIRST, then reset the poppets to unload the gear just before the stop. Change tire size or wheel cut and you re-do both.
• Kingpins and wheel bearings, measured right. Axle off the ground: shake at 12 and 6 for kingpin/bearing, at 3 and 9 for tie rod and linkage. Vertical kingpin play gets a pry bar under the tire with a dial indicator on the axle boss - roughly 1/8 in. is the CVSA out-of-service line, and most makers want a lot tighter. Wheel bearing adjustment follows TMC RP 618: torque the nut while rotating, back off, re-torque light, lock it, and verify 0.001 to 0.005 in. endplay on a dial indicator. Not by feel.
• Suspension: leaf, air, and torque rods. A cracked or broken main (top) leaf is an out-of-service item on its own, and so is a quarter of the leaves broken or missing. On air ride, ride height is a spec, not a preference - set the leveling valve linkage to the axle-to-frame dimension, let it settle, and check it before you ever put the bus on an alignment rack. Worn rear torque rod bushings let the axle walk, which reads as dog tracking, a wandering rear, and driveline vibration.
• Alignment: caster, cross-caster, toe, and thrust angle. Steer axle typically wants positive caster in the 2 to 4 degree range with the sides within about half a degree, or it pulls to the low-caster side. Toe-in is small - think 1/16 to 1/8 in. on a loaded, rolled bus - and caster gets corrected with tapered shims between the spring pad and the axle. Rear thrust angle is what makes a bus track crooked with the wheel off center, and it is not fixed at the front.
• Tires and wheels, school-bus specific. FMCSA 393.75 says no regrooved, recapped, or retreaded tires on the front wheels of a bus, tread depth or not. Steer tires need 4/32 in. in the major grooves, everything else 2/32. Read wear patterns: feather edge equals toe, one shoulder equals camber, center wear equals overinflation, both shoulders equals underinflation, cupping equals shocks/balance/loose bearings. On hub-piloted wheels use clean dry threads and torque to spec (commonly 450 to 500 ft-lb on M22 flange nuts) - no anti-seize on the nut face.

Where techs lose points on S5

Good technicians miss these — not from lack of skill, but because the question is built to catch them.

• "Excessive free play means replace the steering gear." It almost never does. On S5 the question usually hands you a symptom plus a clue - a clunk over bumps, lash that changes with wheel position, play you can see at the slip joint. The answer is the intermediate shaft U-joint, the pitman/drag link socket, or a loose gear mounting bolt. Also do not apply the manual lash number to a power system; power steering allows roughly twice as much.
• Full-lock is not relief pressure. Techs hold the wheel against the stop, read a low number, and condemn the pump. That is the poppet doing its job. And the opposite mistake bricks a job: someone backs the axle stops out for a tighter turning radius on a route, never resets the poppets, and now the gear hydraulically binds at lock, overheats the fluid, and kills the pump in a month. Stops first, poppets second, always.
• "Cupped tires equals bad shocks." Sometimes. But on a steer axle, cupping also comes from out-of-balance assemblies, a loose or improperly adjusted wheel bearing, a bent wheel, or worn kingpins letting the tire wobble. Read the whole stem of the question - if it mentions bearing endplay or a shimmy at a specific speed, shocks is the plausible-looking wrong answer.
• Pull versus off-center versus dog track are three different problems. A bus that pulls points at cross-caster (or cross-camber, or a dragging brake). A bus that tracks straight with the wheel off center is a drag link adjustment. A bus that tracks crooked with the wheel straight is rear axle thrust angle - worn torque rod bushings, a broken spring center bolt, a shifted axle. Fixing any of those at the tie rod is the trap, because the tie rod only sets toe.

A study plan that works for S5

Roughly two weeks of real preparation, in the order that actually builds on itself.

1. Days 1-4: Steering, because it is the biggest block. Column and intermediate shaft, integral gear internals (TRW/Ross and Sheppard), linkage, and the hydraulic side. Actually do a pressure/flow test procedure on paper: gauge placement, shutoff valve, 5-second rule, what the reading means at idle, at relief, and at full lock. Memorize the 393.209 lash table both columns.
2. Days 5-7: Suspension and frame. Leaf spring components and the out-of-service leaf rules, spring hangers, bushings, U-bolts and center bolts, shocks, torque rods, and air ride: leveling valve, dead band, ride height procedure, bag and line leaks. Walk a bus in your shop and put hands on each of these while you name them.
3. Days 8-10: Alignment plus wheels, tires, bearings. Caster, cross-caster, camber, toe, thrust angle, shims, and what each one does when it is wrong. Then the tire wear chart until it is reflex, TMC RP 618 bearing endplay, hub-piloted vs stud-piloted wheels, and FMCSA 393.75 tread depth and the no-retread-on-a-bus-steer rule.
4. Days 11-14: Practice questions only, then chase what you miss. Pull the ASE S5 task list and score yourself line by line - anything you cannot explain out loud to another tech goes back on the list. Spend one of these days riding along on a real annual/CVSA inspection if you can; the out-of-service criteria are half the test's diagnostic logic.

Sample S5 questions

Straight from the bank — answers highlighted, with the explanation underneath.