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Suspension, Steering & Alignment
Rides right. Handles right. Wears right.
18 skill areas
60 key concepts
$0 to learn
Suspension, Steering & Alignment covers the chassis systems that keep vehicles safe and comfortable. Includes basic alignment theory even though most mobile mechanics don't do wheel alignments themselves. Everything below is free — no login, no paywall. Work through the skill areas, drill them in Study Mode, and when you're ready, prove it with the certification exam.
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Drill all 60 concepts in Study Mode. Mark each one “Got it” once you know it cold. When every concept is cleared, you're ready for the SUS exam.
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What you'll be able to do
- Strut and shock diagnosis and replacement
- Control arms, ball joints, tie rods, sway bar links
- Rack and pinion service, power steering diagnosis
- Wheel bearings and hubs
- Alignment theory: caster, camber, toe, thrust angle
- Ride height and adjustable suspension systems
- CV axles and driveline vibration diagnosis
Skill areas
Jump to any area — each one distills the concepts you need to master it.
Fundamentals
1 concept- Suspension isolates the chassis while maintaining tire-to-road contact for grip, braking, and steering control.
Alignment
14 concepts- Excessive camber wears the inner or outer edge; incorrect toe scrubs the tread across its full width — both cause rapid tire wear.
- Positive camber tips the top of the wheel outward. Most modern vehicles run slight negative camber for cornering grip.
- Vehicles pull toward the side with less positive caster. A cross-caster imbalance is a classic pull cause once tire, brake drag, and road crown are ruled out.
- Toe-in: fronts of tires angle toward each other. Toe-out: they angle away. Small toe settings compensate for suspension movement under load.
- Thrust angle is the rear axle's pointing direction vs. the geometric centerline. Non-zero thrust causes a crab-walk and requires a thrust-angle or four-wheel alignment.
- Setback measures whether one front wheel sits farther back than the other. Excess setback usually indicates collision damage to the frame or a subframe.
- SAI is the inward tilt (viewed from the front) of the steering axis. It contributes to steering return, straight-ahead stability, and is a diagnostic angle.
- Steering wheel position is set by the split of toe between the two tie rods. Center the wheel and re-adjust toe evenly to correct it.
- After alignment, tie rod work, or SAS replacement, the steering angle sensor must be re-zeroed. Most scan tools have this procedure.
- More positive caster increases steering effort and centering force. It also improves straight-line stability at speed.
- Caster isn't directly measurable — it's calculated by measuring camber at two steering positions (typically ±10° or ±20°) and applying trig.
- MacPherson camber adjustment is done at the strut mount — either eccentric cams at the knuckle-to-strut bolts or slotted upper mounts.
- A tire with an internal defect can pull the vehicle. Swapping front tires side-to-side confirms it — if the pull follows the tire, it's the tire.
- With camber and toe in spec, the remaining alignment cause is caster (cross-caster split). If caster is also good, check for a radial pull tire.
Shocks & Struts
5 concepts- Springs absorb road impacts; shocks (or the shock portion of a strut) dampen the resulting oscillations so the tire settles back on the road quickly.
- A strut is a structural component that supports the vehicle, locates the wheel, and dampens motion — replacing an upper control arm in MacPherson designs.
- Strut replacement disturbs camber and often SAI. An alignment is required after every strut replacement.
- Push down hard on a corner and release. A healthy shock lets the vehicle rise back and stop within 1-2 oscillations. More than that indicates worn dampers. It's a rough check — not definitive.
- Struts fail most often via seal wear — the oil in the strut leaks past the shaft seal, reducing damping progressively.
Ball Joints
2 concepts- To test a loaded ball joint, you must unload it. Support the load-bearing control arm (upper in this case) at the coil spring location, then check for play.
- Wear-indicator joints have a raised nipple that recedes as the joint wears. When it's flush with or below the housing under vehicle load, replace the joint.
Tie Rods
2 concepts- A worn inner tie rod causes play in the steering linkage, producing clunks on turn-in, wander, and often uneven tire wear.
- Outer tie rod length directly sets toe. After replacement, toe must be reset — full alignment is best practice.
Wheel Bearings
3 concepts- Turning right unloads the right bearing and loads the left. If noise gets louder turning right (load on left), the LEFT bearing is bad. Standard rule: bad bearing is on the OPPOSITE side of the direction that makes it louder.
- Sealed bearings require specific axle nut torque per manufacturer spec — often high values (150-250 ft-lb). Under- or over-torque destroys the bearing.
- Many modern bearings have integrated WSS or magnetic encoder rings. If the encoder ring is damaged, ABS/traction faults follow.
Springs
4 concepts- Ride height is set by the spring. A broken coil, sagged spring, or (on trucks) a broken leaf reduces ride height at that corner.
- Spring compressors contain the enormous stored energy in a coil spring during strut disassembly and reassembly. Skipping them can be fatal.
- An electric air compressor (usually underbody or in a wheel well) supplies pressurized air to the air springs, controlled by ride height sensors.
- Air suspensions can activate and lift/lower the vehicle unexpectedly. Disable via the service switch or fuse before working underneath.
Sway Bars
2 concepts- A sway bar links opposite wheels through a torsion bar, transferring load between them during cornering to reduce body roll.
- Sway bar end link and bushing wear produce distinctive clunks over small bumps at low speed — a common misdiagnosis often blamed on struts.
Control Arms
2 concepts- Control arm bushings allow the arm to pivot through its arc while damping road vibration into the chassis.
- Bushings resist torsion. If bolted at full droop, they'll be pre-loaded when the vehicle sits, causing premature failure. Torque at ride height puts them at neutral.
Power Steering
3 concepts- Low or wrong fluid is the most common cause. Always check level and confirm correct fluid type before replacing components.
- EPS uses a torque sensor (usually in the column) to detect driver input and modulate the assist motor's output.
- EPS torque sensors typically require a zero-point calibration relearn after replacement, done with a scan tool.
Steering Rack
2 concepts- Fluid in an inner tie rod boot means the rack's internal seal has failed. The rack (or its seal kit) must be serviced.
- Toe is split between left and right tie rods relative to a centered steering wheel. If not centered, the wheel will sit off-center after alignment.
Tires
3 concepts- Inner-edge wear on both sides is the classic pattern for excessive negative camber or toe-out. Toe issues wear one edge more than the other; camber wears the same edge on both.
- Cupping happens when the tire hops as it rolls — bad dampers or balance are the top causes. Fix the underlying issue before replacing the tire.
- Directional tires must stay on the same side. Rotate front-to-back on the same side only, unless the tires are dismounted and reversed.
Steering
5 concepts- Clicking near steering lock at low speed under acceleration is classic outer CV joint wear — often misdiagnosed as steering.
- Worn intermediate shaft U-joints or slip joints in the steering column rattle over rough roads. Common on many trucks and SUVs.
- Wrong fluid can swell seals, damage the pump, or cause noise. Always use the exact fluid specified by the manufacturer.
- Air causes cavitation and whine. Vehicle-specific bleed procedures (turning wheel lock-to-lock with engine off or on) usually work air out.
- Dry-park test: with the vehicle on the ground, have someone rock the steering wheel while you watch each joint for play. Reveals worn tie rods, idler arms, ball joints, and racks.
Diagnostics
5 concepts- Speed-related steering wheel vibration is almost always tire balance, wheel runout, or force variation issues. Check the tires and wheels first.
- Memory steer is a binding condition — the upper strut mount, strut bearing, or a stiff ball joint prevents the wheels from centering.
- Low-speed shimmy that disappears at higher speed often points to driveline balance or a bent wheel/tire imbalance. Inspect driveshaft, U-joints, and wheels.
- Bent dust shields or loose heat shields are the top causes of scraping when turning. Straighten or replace, and confirm before deeper diagnosis.
- Truck clunks on shift can come from worn leaf bushings, loose U-bolts, or worn drivetrain mounts. Inspect the whole load path.
Fasteners
2 concepts- TTY bolts stretch permanently when torqued to spec. Reuse loses clamping force and risks failure. Always replace.
- Pressed-in ball joints require a hydraulic press and adapters. Hammering damages the arm and rarely works.
Suspension Types
2 concepts- Short-Long Arm (SLA) or double-wishbone uses independent upper and lower control arms. Ideal for camber control across the suspension travel.
- Multi-link designs use separate links to control each degree of freedom (typically 3-5 links per side), giving better handling and packaging vs. simpler designs.
Safety
2 concepts- Once a boot tears, water and grit reach the bearing. Damage is invisible until it fails. Replace to avoid catastrophic separation.
- Corrosion pits are stress concentrators. Coil failures usually happen without warning and can destroy tires, brake lines, or send parts through the fender.
Regulation
1 concept- Commercial vehicles are inspected against Federal Motor Carrier Safety Administration or CVSA out-of-service criteria — steering play, cracked components, and broken springs all trigger fail.
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