Michigan CDL Combination cheat sheet

Pre-trip inspection covers three areas: engine compartment, cab and controls, and walk-around exterior (lights, tires, coupling, cargo).

Tire rule: minimum tread depth 4/32 inch on front steer tires and 2/32 inch on all other tires; no cuts, bulges, or exposed cord.

Air brake leak test: with engine off and full pressure, loss must not exceed 3 psi in one minute for a single vehicle or 4 psi for a combination.

Applied (leak-down) test: apply full brake, hold one minute; loss must not exceed 4 psi. Low-pressure warning must sound by 60 psi.

Slack adjuster check: with brakes released and pushed by hand, movement at the chamber push rod should be about 1 inch or less (under 1/4 of the rod's free stroke limit).

Coupling inspection: fifth wheel jaws fully closed around the kingpin, no gap between upper and lower fifth wheel plates, release handle in the locked position.

Lighting check: clearance, identification, marker, turn signal, four-way flasher, brake, tail, and license plate lights all functional.

Emergency equipment: charged fire extinguisher, spare fuses, and three reflective triangles (or six fuses) required.

Total stopping distance = perception distance + reaction distance + brake lag distance + braking distance.

At 55 mph, brake lag on air brakes adds roughly 32 feet before the brakes even apply, versus about 11 feet for hydraulic brakes.

Perception distance at 55 mph is about 60 feet and reaction distance about 61 feet, before any braking begins.

Brake lag distance = speed (mph) x 1.1 feet, approximately, for air brake systems at 55 mph.

Shift down before a downgrade; do not ride the brakes. Use engine braking and a lower gear to control speed.

Stab braking (push hard, release, repeat) is the correct technique when brakes get hot and fade; do not fan or pump lightly.

Retarders help on downgrades but may be illegal on slippery surfaces; they do not replace service brakes.

When the wheels are straight, the combination is at its shortest length; turning increases the space needed.

Coupling sequence: inspect fifth wheel, back under trailer, secure tractor, connect air lines and electrical cord, lock jaws, raise landing gear, test pull.

The pull test: after locking jaws, apply trailer spring brakes, pull forward gently with the tractor to confirm the kingpin is captured.

Before backing under the trailer, the fifth wheel should be greased and the jaws open; the trailer should be at roughly the same height as the fifth wheel.

Uncoupling sequence: park, chock wheels, lower landing gear, disconnect air lines and electrical cord, release fifth wheel jaws, pull forward slowly.

Raise landing gear until it firmly contacts the ground and the trailer is supported before releasing the fifth wheel.

When disconnecting, place the electrical cord and air lines so they are not crushed or dragged; secure them to the tractor.

After uncoupling, the trailer should be supported by landing gear with the fifth wheel plate free of the kingpin.

Missing or damaged safety latches on the fifth wheel mean the coupling is not secure; do not drive.

Two separate air systems (primary and secondary) provide redundancy; a failure in one leaves some braking available.

Low air pressure warning must activate before pressure drops below 60 psi; at that point, a buzzer or light signals the driver.

The spring brakes (emergency/parking brakes) apply automatically when air pressure drops to roughly 20-45 psi.

Tractor protection valve closes automatically during a trailer breakaway, sealing the tractor's air supply so it retains pressure.

The trailer hand valve (trolley valve) should be used only to test trailer brakes, never to park; it can leak and release brakes.

The supply line (emergency line) charges the trailer; the service line (control line) applies trailer brakes.

To test trailer brakes, charge the system, apply the tractor hand valve, and walk back to listen for brake application.

Drain air tanks daily to remove moisture; moisture in the system can freeze and cause brake failure.

Air compressor builds pressure to governor cut-out (about 120-125 psi) and restarts at cut-in (about 100 psi).

Off-tracking: the rear wheels of a combination follow a shorter path than the front wheels; a long combination can off-track by several feet.

Rule of thumb: a 53-foot trailer can off-track by up to about 3 feet in a standard turn; wider turns are required.

Swing-out: the rear of the tractor and the front of the trailer swing outward opposite the turn direction; check mirrors before turning.

When backing a trailer, steer the top of the steering wheel in the direction you want the trailer to go.

Back toward the driver's side (left) whenever possible for better visibility; use a spotter and GOAL (Get Out And Look).

Pull forward to correct a backing error rather than oversteering; small steering inputs at slow speed.

Right turns: swing wide to the left but not into oncoming traffic; a large combination may need both lanes.

Mirror use: check both mirrors before and during turns; the trailer's rear wheels are not visible in the mirror at all times.

A skid happens when tires lose traction; causes include overbraking, oversteering, and driving too fast for conditions.

To recover from a drive-wheel (rear) skid: stop braking, steer in the direction you want to go, and avoid overcorrecting.

Front-wheel skid: the vehicle will not respond to steering; ease off the accelerator and brake gently to regain traction.

Trailer skid (jackknife): release the brakes to let the trailer wheels roll and regain traction, then steer to straighten.

Brake steer (trailer swing) can be caused by applying the trailer hand valve; avoid using it while driving.

Anti-lock braking systems (ABS) prevent wheel lockup; do not pump the brakes on ABS-equipped vehicles.

On slippery surfaces, reduce speed and increase following distance; stopping distance can double or triple.

If a trailer begins to jackknife, do not apply more braking; steer and release brakes to regain control.

Cargo must be secured so it cannot shift; the aggregate working load limit of tiedowns must be at least 50% of the cargo weight.

Minimum tiedowns: one for cargo up to 1,100 lbs, two for 1,100-2,200 lbs, and three for over 2,200 lbs (per federal rules).

Weight distribution: keep the center of gravity low and centered; too much weight on the rear can make steering light.

Axle weight limits: steer axle typically 12,000 lbs, drive tandems 34,000 lbs, trailer tandems 34,000 lbs; gross up to 80,000 lbs.

Bridge formula limits weight per axle group based on the distance between axles.

Check cargo securement after the first 50 miles and every 150 miles or 3 hours thereafter.

Front axle overload reduces steering control; rear axle overload can cause tire failure and poor braking.

Headache rack and load locks prevent forward load shift into the cab during hard braking.

Following distance: at least one second per 10 feet of vehicle length at speeds under 40 mph; add one second for speeds over 40 mph.

A 60-foot combination at 55 mph needs at least 7 seconds of following distance.

Look 12-15 seconds ahead of the vehicle to spot hazards early.

Space cushion: keep space to the front, sides, and rear; avoid driving in another vehicle's blind spot.

When entering a curve, slow down before the curve, not in it; braking in a curve can cause a skid.

Railroad crossings: slow down, look both ways, and do not stop on the tracks; a combination may need extra clearance.

Use four-way flashers when driving slowly on a highway or when stopped in a hazardous position.

Downhill grade: select a gear that holds speed without braking; if brakes fail, use an escape ramp.

Night driving: reduce speed and increase following distance; visibility is reduced and fatigue is higher.