Regulation
On commercial vehicles, suspension condition isn't a judgment call — it's regulated.
- 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.
Techs inspecting trucks and buses work against published federal criteria, and knowing where those standards come from is part of the job.
FMCSA and CVSA Standards
Commercial vehicle inspections measure suspension and steering components against Federal Motor Carrier Safety Administration (FMCSA) regulations and the Commercial Vehicle Safety Alliance (CVSA) out-of-service criteria — not against shop opinion or whatever a tech thinks looks acceptable. These published standards define specific wear limits and load-carrying requirements: maximum allowable steering wheel free play, cracked or broken suspension components, broken or missing spring leaves, and compromised load-bearing parts are all defined conditions that trigger a failed inspection or place the vehicle out of service on the spot.
For the working tech, the practical meaning is that commercial suspension work carries a documentation and compliance layer that passenger car work doesn't. A cracked hanger, a shifted leaf, or excessive steering lash on a truck isn't a 'recommend repair' line item — it can be a violation that grounds the vehicle until repaired. Know the CVSA out-of-service criteria for the components you touch, inspect to the published limit rather than to feel, and document what you measured. When a DOT roadside inspection finds what you missed, the paper trail matters.
| Steering wheel diameter | Manual steering max lash | Power steering max lash |
|---|---|---|
| 16 in. or less | 2 in. | 4-1/2 in. |
| 18 in. | 2-1/4 in. | 4-3/4 in. |
| 20 in. | 2-1/2 in. | 5-1/4 in. |
| 22 in. | 2-3/4 in. | 5-3/4 in. |
Power-steering lash is measured with the engine running. CVSA out-of-service criteria are updated annually — always inspect to the current published edition.
- Measure steering wheel lash with the wheels straight ahead and the engine running on power-steering vehicles. Rock the wheel until the tires just begin to move each way — travel beyond the table limit for that wheel diameter is a defined violation, not a judgment call.
- Inspect every spring assembly against the criteria: cracked or broken leaves, a broken main leaf, leaves shifted out of position or contacting a moving part — each is a defined condition with a defined consequence.
- Work through hangers, U-bolts, torque arms, and attachment points for cracks, looseness, and missing fasteners. On commercial equipment these are compliance items, not 'recommend' lines.
- Record what you measured, not just what you concluded — the measured lash, the specific leaf, the photo. When a roadside inspection follows your work, the paper trail is your defense.
- Anything at or past an out-of-service limit grounds the vehicle until repaired. Write it that way and hold the line — releasing an OOS-condition truck puts your certification and the public on the same road.
- Inspecting commercial suspension to feel and shop opinion instead of the published FMCSA/CVSA limits — 'looks okay to me' is not a defense when the roadside inspection finds the defined defect you passed.
- Working from an outdated out-of-service criteria edition. The CVSA updates annually, and inspecting to last decade's limits is inspecting wrong.
- Writing an out-of-service condition as 'recommend repair.' A defined OOS condition grounds the vehicle — softening the language transfers the liability to you.
- Skipping documentation of measured values — without the recorded lash measurement or photo, your inspection is your word against a violation notice.
A truck with a 20-inch steering wheel and power steering shows 5-1/2 inches of lash with the engine running. What is the call?
It exceeds the 5-1/4 in. limit for a 20-inch wheel under 49 CFR 393.209, so it is a violation and, at that level, an out-of-service condition — the vehicle does not go back in service until the steering lash is corrected. Measure and record the value; the number is the finding.
You find one broken leaf in a multi-leaf spring pack on a trailer. Is the vehicle automatically out of service?
Not automatically — under the CVSA criteria, out-of-service is typically triggered by a broken main leaf or one-fourth or more of the leaves in the assembly broken. A single broken non-main leaf is still a federal defect requiring repair, just not necessarily OOS. Verify against the current edition and document exactly which leaf, because the distinction decides whether the truck moves.
A truck with a 20-inch steering wheel and power steering shows 5-1/2 inches of lash with the engine running. What is the call?
Missed one? The reasoning above comes straight from the SUS exam bank, so this is the standard you will be held to.