CDL Vehicle Inspection Answers: Shut-Off Valves, Wheel Bearing Seals, Suspension, Tires

TLDR The most-asked CDL pre-trip inspection questions resolve to a handful of answers: shut-off valves close the air lines and are located at the rear of the trailer (and at the front where the glad hands connect); wheel bearing seals are checked for leaks; suspension defects include cracked spring hangers, missing leaf spring leaves, and leaking shock absorbers; and the signs of tire failure are sound, vibration, and heavy steering. Last updated August 2026.

The CDL pre-trip vehicle inspection test is where knowledge-exam and skills-test material overlap, and a small set of questions keeps appearing on both: where the shut-off valves are, what wheel bearing seals are checked for, which suspension system defects to look for, what counts as a sign of tire failure, and what spring brakes are held back by. Each has one right answer straight from the Florida CDL Handbook's vehicle inspection chapter, and all of them are collected in the table and sections below so you can study the whole cluster in one pass. Last updated August 2026.

The Inspection Questions, Answered in One Table

Shut-Off Valves: What They Are and Where They Live

A shut-off valve is a valve in the air line that lets you close that line - manually or automatically. On a tractor-trailer, the lines terminate in glad hands at the front of the trailer, and shut-off valves sit in the lines where they can isolate each segment. The location detail the exam wants: at the rear of the trailer, which is exactly where shut-off valves matter most on multi-trailer combinations. In a doubles or triples setup, air has to flow through each trailer to reach the ones behind it, so the shut-off valves on all but the last trailer stay open, and the shut-off valves at the rear of the last trailer stay closed - nothing is connected behind it, so leaving them open would vent the system. That open-or-closed question ("shut-off valves at the rear of the last trailer should be ___") is one of the most frequently missed combination-vehicle questions, and the answer is closed.

Wheel Bearing Seals: The Leak Check

On the walkaround inspection, each wheel hub gets two checks: hub oil level OK and no leaks. Wheel bearing seals are checked specifically for leaks - oil seeping around the seal means the bearing is losing its lubrication, and a bearing that runs dry can seize or let the wheel assembly fail. The related check on the same corner of the vehicle: rust-streaked lug nuts indicate looseness (test them with a wrench), and after a tire has been changed you stop a short while later and re-check the nut tightness. Put together, the wheel-end inspection is a leak-and-looseness inspection - and "leaks" is the one-word exam answer for the seals.

Suspension System Defects: The Full List

The suspension system holds up the vehicle and its load and keeps the axles in place, which is why broken suspension parts are extremely dangerous. The handbook's defect list to look for:

• Spring hangers that allow movement of the axle from its proper position.
• Cracked or broken spring hangers.
• Missing or broken leaves in any leaf spring - if one-fourth or more are missing, the vehicle is out of service, but any defect could be dangerous.
• Broken leaves in a multi-leaf spring, or leaves that have shifted so they might hit a tire or other part.
• Leaking shock absorbers.
• Torque rod or arm, u-bolts, spring hangers, or other axle-positioning parts that are cracked, damaged, or missing.
• Air suspension systems that appear damaged or are leaking.

Any of these changes how the axles track under the vehicle - and an axle that moves is a tire-wear, braking, and steering problem all at once.

Tire Failure: The Three Signs and the Response

Recognizing tire failure quickly buys you the seconds to react. The three major signs:

1. Sound. The loud bang of a blowout is the obvious one - and because it takes a few seconds for your vehicle to react, you might think the noise came from another vehicle. Any time you hear a tire blow, assume it is yours.
2. Vibration. Heavy thumping or vibration may mean a tire has gone flat. With a rear tire, that may be the only sign you get.
3. Feel. Steering that feels "heavy" is the classic sign of a failed front tire; a rear-tire failure can make the vehicle slide back and forth or fishtail, though dual rear tires usually prevent that.

The response, in order: hold the steering wheel firmly (a front blowout can twist the wheel out of your hands), stay off the brake, let the vehicle slow on its own, and pull off the road when it is under control. The inspection-side prevention is the tread and pressure checklist - correct air pressure, no cuts or bulges, no tread separation, and the 4/32-inch front and 2/32-inch other-tire tread minimums.

Spring Brakes: Held Back by Air

The spring brake question closes the cluster. A powerful spring is built into the brake chamber and constantly wants to apply the brake; compressed air pressure holds the spring back and keeps the wheels rolling during normal operation. When system pressure falls to the threshold, the spring applies the brakes mechanically - no air required. That fail-safe design is why the low-air warning matters: the air is the only thing keeping the springs off the brakes, and you want the warning to tell you about falling pressure while there is still enough air to stop under control.

The Seven-Step Method Ties It All Together

The handbook teaches the pre-trip inspection as a fixed seven-step method performed the same way every time, so nothing gets skipped: approach the vehicle and note its general condition, check the engine compartment, start the engine and check inside the cab, turn the engine off and check the lights, do the walkaround, check the signals, and finish with the brake checks. The wheel-end, suspension, and valve questions above are all walkaround items - learn where they live in the sequence and they stop being a random list.

Frequently Asked Questions

Where are shut-off valves on a CDL vehicle?

They are in the air lines and are used to close the lines - located at the rear of the trailer, with the glad hands at the front. On multi-trailer combinations the shut-off valves at the rear of the last trailer are closed, and all others are open so air flows through to the rear.

What should wheel bearing seals be checked for?

Leaks. The walkaround check is hub oil level OK and no leaks around the seals - oil loss means the bearing is losing lubrication and can seize.

What suspension system defects should you look for?

Spring hangers that let the axle move from position, cracked or broken spring hangers, missing or broken leaf spring leaves (one-fourth or more missing means out of service), leaking shock absorbers, and cracked, damaged, or missing torque rods, u-bolts, or other axle-positioning parts.

What are the signs of tire failure?

Sound (the loud bang of a blowout), vibration (heavy thumping, possibly a flat rear tire), and feel (steering feels heavy - a front tire failure - or the vehicle fishtails from a rear tire). Respond by holding the wheel firmly and staying off the brake while the vehicle slows.

What holds spring brakes back?

Air pressure. The spring applies the brake mechanically whenever air pressure drops; during normal operation compressed air holds the spring compressed and the wheels roll free.

Drill the Whole Inspection Chapter

These questions come straight from the inspection chapter of the handbook, and the fastest way to hold them is to read the source once and then drill the question forms: start with the Florida CDL Handbook's vehicle inspection section, then test yourself with LowestPriceTrafficSchool's CDL/DMV prep course until the one-word answers - leaks, closed, air pressure - are automatic.

Citations

• https://www.lowestpricetrafficschool.com/handbooks/cdl/en/2/1
• https://www.lowestpricetrafficschool.com/handbooks/cdl/en/2/17
• https://www.fmcsa.dot.gov/registration/commercial-drivers-license