LA CDL Combination cheat sheet

Pre-trip inspection order for a tractor-trailer: left front of tractor, left side and coupling area, right side and rear of tractor, right side of trailer, rear of trailer, then brakes and in-cab items.

Fifth wheel inspection points: securely mounted to frame, jaws closed and locked around the kingpin, locking lever in the locked position, no gap between apron and trailer plate, pivot pins secure, mounting bolts tight.

Kingpin inspection: firmly attached to the trailer apron, free of bends, cracks, and excessive wear; a worn or damaged kingpin can allow the trailer to separate under load.

Tilt-test method: with the trailer brakes released and the tractor brakes set, pull gently against the locked kingpin; movement or a clunk indicates the jaws are not fully locked.

Coupling sequence: inspect, align the tractor squarely with the trailer, back slowly under the trailer, listen for the click, tug test twice, visually check the jaws, connect air lines and electrical cord, raise landing gear, secure the release lever.

Air line connection: connect the emergency (supply) line first, then the service line; the emergency line supplies trailer air tanks and triggers trailer spring brakes if it separates.

Uncoupling sequence: park on firm level ground, apply parking brakes, chock wheels, lower landing gear to firm contact, disconnect lines and cord, pull the release lever, drive slowly forward until clear of the trailer.

Landing gear must be fully raised before moving, with the crank handle secured; a partially raised crank handle can strike the ground or a person.

After coupling, check that the trailer is at the correct height and the tractor frame is not contacting the trailer; verify all lights operate and the trailer brakes release and hold.

Off-tracking: the rear wheels of a combination follow inside the path of the front wheels; the longer the wheelbase and trailer, the greater the off-track, so swing wide before completing a turn.

Right turns require a wide left setup and a check of the right mirror through the turn; a vehicle in the right lane may be hidden in the blind spot where the trailer cuts inside.

Swing-out: the rear of the tractor or the front of the trailer can swing outward during a tight turn, endangering vehicles and pedestrians beside the tractor.

Braking distance for a combination is longer than for a single vehicle; a loaded combination requires substantially more stopping distance than an empty one, and the trailer can push the tractor in a panic stop.

Minimum following distance for a combination under 40 mph is one second per 10 feet of vehicle length plus one second; above 40 mph add one additional second.

Speed on curves and ramps must be reduced before entering; braking while turning on a curve risks a jackknife or trailer skid because the tires are already at their traction limit.

Downgrades: select a gear low enough that the engine and retarder hold the speed, brake on the straight sections, and never coast in neutral or with the clutch disengaged.

Lane changes require a longer gap than a single vehicle; check mirrors on both sides, signal early, and confirm the trailer has cleared the lane before returning.

Rollover and jackknife avoidance: keep the center of gravity low, slow before curves, and steer smoothly without abrupt correction at highway speed.

Static leak test: with the engine off and the system charged, release the parking brakes, hold the service brake for one minute, and the pressure drop must not exceed 3 psi for a single vehicle or 4 psi for a combination.

Applied (leakage rate) test: with the brakes fully applied and the engine off, a pressure loss of more than 3 psi in one minute for a combination indicates a leak that must be repaired.

Low-air warning: the warning buzzer and light must activate before the pressure falls below 60 psi; if they do not, the system is defective.

Spring brake test: with the engine off, pump the brake pedal to reduce pressure; the trailer spring brakes must set at about 45 psi and the tractor spring brakes at about 20 to 45 psi.

Tractor protection valve test: with the system charged, close the trailer air supply valve or disconnect the emergency line; the trailer spring brakes must set and the tractor must not lose air.

Trailer brake check: with the trailer supply line connected and charged, apply the hand valve or trailer brake control; the trailer brakes must engage and hold while the tractor is unaffected.

Air compressor build-up: with the engine at operating rpm and the system low, pressure must rise from 85 to 100 psi within 45 seconds in a combination vehicle.

Governor cut-out should be around 120 to 125 psi and cut-in around 100 psi; the system must not exceed the safety valve setting of about 150 psi.

If a trailer has no air pressure, its spring brakes remain applied; a trailer left uncoupled and uncharged cannot be moved until it is supplied with air or the brakes are caged.

Axle weight limits: steer axle 12,000 lb, each drive axle 20,000 lb, each trailer axle 20,000 lb, and gross combination weight 80,000 lb on California highways without an oversize permit; always check the bridge formula and posted scales.

California requires the cargo to be secured so it cannot shift or fall; aggregate tiedown working load limits must equal at least half the cargo weight, and the frontmost tiedown must prevent forward movement.

Cargo must be distributed so no axle is overloaded; place heavy freight over or slightly ahead of the drive axles and keep the trailer floor load balanced side to side.

High center of gravity raises rollover risk; heavy loads should be placed low and centered, and liquids in partially filled tanks shift and can cause a rollover on a curve.

Rollover threshold for a loaded combination is often below 0.4 g lateral acceleration; posted ramp speeds are calculated for passenger cars and may exceed a loaded truck's safe speed.

The bridge formula limits weight per axle group based on the distance between axles; adding axles or increasing spacing raises the allowable weight.

Cargo must not obscure lights, reflectors, or the license plate, and must not extend more than 4 feet beyond the rear of the trailer without a red or orange flag and, at night, a light.

Load securement must be checked within the first 50 miles and every 150 miles or 3 hours thereafter, and after any hard braking or evasive maneuver.

Pre-trip inspection order for a tractor-trailer: left front of tractor, left side and coupling area, right side and rear of tractor, right side of trailer, rear of trailer, then brakes and in-cab items.

Fifth wheel inspection points: securely mounted to frame, jaws closed and locked around the kingpin, locking lever in the locked position, no gap between apron and trailer plate, pivot pins secure, mounting bolts tight.

Kingpin inspection: firmly attached to the trailer apron, free of bends, cracks, and excessive wear; a worn or damaged kingpin can allow the trailer to separate under load.

Tilt-test method: with the trailer brakes released and the tractor brakes set, pull gently against the locked kingpin; movement or a clunk indicates the jaws are not fully locked.

Coupling sequence: inspect, align the tractor squarely with the trailer, back slowly under the trailer, listen for the click, tug test twice, visually check the jaws, connect air lines and electrical cord, raise landing gear, secure the release lever.

Air line connection: connect the emergency (supply) line first, then the service line; the emergency line supplies trailer air tanks and triggers trailer spring brakes if it separates.

Uncoupling sequence: park on firm level ground, apply parking brakes, chock wheels, lower landing gear to firm contact, disconnect lines and cord, pull the release lever, drive slowly forward until clear of the trailer.

Landing gear must be fully raised before moving, with the crank handle secured; a partially raised crank handle can strike the ground or a person.

After coupling, check that the trailer is at the correct height and the tractor frame is not contacting the trailer; verify all lights operate and the trailer brakes release and hold.

Off-tracking: the rear wheels of a combination follow inside the path of the front wheels; the longer the wheelbase and trailer, the greater the off-track, so swing wide before completing a turn.

Right turns require a wide left setup and a check of the right mirror through the turn; a vehicle in the right lane may be hidden in the blind spot where the trailer cuts inside.

Swing-out: the rear of the tractor or the front of the trailer can swing outward during a tight turn, endangering vehicles and pedestrians beside the tractor.

Braking distance for a combination is longer than for a single vehicle; a loaded combination requires substantially more stopping distance than an empty one, and the trailer can push the tractor in a panic stop.

Minimum following distance for a combination under 40 mph is one second per 10 feet of vehicle length plus one second; above 40 mph add one additional second.

Speed on curves and ramps must be reduced before entering; braking while turning on a curve risks a jackknife or trailer skid because the tires are already at their traction limit.

Downgrades: select a gear low enough that the engine and retarder hold the speed, brake on the straight sections, and never coast in neutral or with the clutch disengaged.

Lane changes require a longer gap than a single vehicle; check mirrors on both sides, signal early, and confirm the trailer has cleared the lane before returning.

Rollover and jackknife avoidance: keep the center of gravity low, slow before curves, and steer smoothly without abrupt correction at highway speed.

Static leak test: with the engine off and the system charged, release the parking brakes, hold the service brake for one minute, and the pressure drop must not exceed 3 psi for a single vehicle or 4 psi for a combination.

Applied (leakage rate) test: with the brakes fully applied and the engine off, a pressure loss of more than 3 psi in one minute for a combination indicates a leak that must be repaired.

Low-air warning: the warning buzzer and light must activate before the pressure falls below 60 psi; if they do not, the system is defective.

Spring brake test: with the engine off, pump the brake pedal to reduce pressure; the trailer spring brakes must set at about 45 psi and the tractor spring brakes at about 20 to 45 psi.

Tractor protection valve test: with the system charged, close the trailer air supply valve or disconnect the emergency line; the trailer spring brakes must set and the tractor must not lose air.

Trailer brake check: with the trailer supply line connected and charged, apply the hand valve or trailer brake control; the trailer brakes must engage and hold while the tractor is unaffected.

Air compressor build-up: with the engine at operating rpm and the system low, pressure must rise from 85 to 100 psi within 45 seconds in a combination vehicle.

Governor cut-out should be around 120 to 125 psi and cut-in around 100 psi; the system must not exceed the safety valve setting of about 150 psi.

If a trailer has no air pressure, its spring brakes remain applied; a trailer left uncoupled and uncharged cannot be moved until it is supplied with air or the brakes are caged.

Axle weight limits: steer axle 12,000 lb, each drive axle 20,000 lb, each trailer axle 20,000 lb, and gross combination weight 80,000 lb on California highways without an oversize permit; always check the bridge formula and posted scales.

California requires the cargo to be secured so it cannot shift or fall; aggregate tiedown working load limits must equal at least half the cargo weight, and the frontmost tiedown must prevent forward movement.

Cargo must be distributed so no axle is overloaded; place heavy freight over or slightly ahead of the drive axles and keep the trailer floor load balanced side to side.

High center of gravity raises rollover risk; heavy loads should be placed low and centered, and liquids in partially filled tanks shift and can cause a rollover on a curve.

Rollover threshold for a loaded combination is often below 0.4 g lateral acceleration; posted ramp speeds are calculated for passenger cars and may exceed a loaded truck's safe speed.

The bridge formula limits weight per axle group based on the distance between axles; adding axles or increasing spacing raises the allowable weight.

Cargo must not obscure lights, reflectors, or the license plate, and must not extend more than 4 feet beyond the rear of the trailer without a red or orange flag and, at night, a light.

Load securement must be checked within the first 50 miles and every 150 miles or 3 hours thereafter, and after any hard braking or evasive maneuver.