Commercial driver’s license (CDL) knowledge tests · California DMV
Coupling and Uncoupling
Questions and answers
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What could happen if the fifth-wheel plate is not kept lubricated?
Steering problems, because of friction between the tractor and trailer
The fifth-wheel plate must be greased as required, or friction can cause steering problems.
Section 6 · Step 1: Inspecting the Fifth-Wheel ↗ -
Before coupling, how should the fifth-wheel be tilted?
Down towards the rear of the tractor
In the proper coupling position the wheel is tilted down toward the rear of the tractor.
Section 6 · Step 1: Inspecting the Fifth-Wheel ↗ -
Before coupling, in what position should the fifth-wheel jaws and the safety unlocking handle be?
Jaws open and the handle in the automatic lock position
The jaws must be open and the safety unlocking handle in the automatic lock position.
Section 6 · Step 1: Inspecting the Fifth-Wheel ↗ -
You have a sliding fifth-wheel. What do you make sure of before coupling?
That it is locked
A sliding fifth-wheel must be locked before you couple.
Section 6 · Step 1: Inspecting the Fifth-Wheel ↗ -
What do you check on the trailer kingpin before coupling?
That it is not bent or broken
The kingpin must not be bent or broken.
Section 6 · Step 1: Inspecting the Fifth-Wheel ↗ -
Before backing under a trailer, what must be true of the trailer wheels?
They are chocked or the spring brakes are on
The trailer must be held by chocks or spring brakes while you couple.
Section 6 · Step 2: Inspect the Area and Chock the ↗ -
What do you check about the cargo before coupling?
That it is secured against movement caused by the tractor being coupled to the trailer
Coupling jolts the trailer, so the cargo must be secured against movement.
Section 6 · Step 2: Inspect the Area and Chock the ↗ -
Where do you position the tractor for coupling?
Directly in front of the trailer
Put the tractor directly in front of the trailer and check your position in the outside mirrors, looking down both sides of the trailer.
Section 6 · Step 3: Position the Tractor ↗ -
Why should you never back under the trailer at an angle?
You might push the trailer sideways and break the landing gear
Backing in at an angle can shove the trailer sideways and break the landing gear.
Section 6 · Step 3: Position the Tractor ↗ -
When first backing toward the trailer, where do you stop?
When the fifth-wheel just touches the trailer
Back slowly until the fifth-wheel just touches the trailer. Do not hit the trailer.
Section 6 · Step 4: Back Slowly ↗ -
What is the correct trailer height for coupling?
Low enough that the trailer is raised slightly by the tractor when the tractor backs under it
The tractor should lift the trailer slightly as it backs under.
Section 6 · Step 6: Check the Trailer Height ↗ -
What may happen if the trailer is too low when you couple?
The tractor may strike and damage the trailer nose
A trailer set too low can be struck by the tractor.
Section 6 · Step 6: Check the Trailer Height ↗ -
What may happen if the trailer is too high when you couple?
It may not couple correctly
A trailer set too high may not couple correctly.
Section 6 · Step 6: Check the Trailer Height ↗ -
Which glad hand does the tractor emergency air line connect to?
The trailer emergency glad hand
Check the glad hand seals, then connect emergency to emergency and service to service.
Section 6 · Step 7: Connect Air Lines to the Trailer ↗ -
How must the air lines be placed before the tractor backs under the trailer?
Safely supported where they will not be crushed or caught
Support the lines so they are not crushed or caught while the tractor backs under.
Section 6 · Step 7: Connect Air Lines to the Trailer ↗ -
How do you supply air to the trailer brake system from the cab?
Push in the “air supply” knob, or move the tractor protection valve control from “emergency” to “normal”
Pushing the air supply knob in sends air to the trailer. Then wait until the air pressure is normal.
Section 6 · Step 8: Supply Air to the Trailer ↗ -
Why do you shut the engine off when checking the brake system for crossed air lines?
So you can hear the brakes
With the engine off you can hear the trailer brakes being applied and released.
Section 6 · Step 8: Supply Air to the Trailer ↗ -
When you apply and release the trailer brakes to check for crossed air lines, what should you hear?
The brakes move when applied and air escape when they are released
You should hear the brakes move on application and air escape on release. Also check the gauge for signs of major air loss.
Section 6 · Step 8: Supply Air to the Trailer ↗ -
How do you lock the trailer brakes before backing under the trailer?
Pull out the “air supply” knob, or move the tractor protection valve control from “normal” to “emergency”
Pulling the air supply knob out locks the trailer brakes.
Section 6 · Step 9: Lock the Trailer Brakes ↗ -
Which gear do you use to back under the trailer?
The lowest reverse gear
Use the lowest reverse gear and back slowly to avoid hitting the kingpin too hard.
Section 6 · Step 10: Back Under the Trailer ↗ -
When do you stop backing under the trailer?
When the kingpin is locked into the fifth-wheel
Stop when the kingpin locks into the fifth-wheel.
Section 6 · Step 10: Back Under the Trailer ↗ -
How do you check that the trailer is locked onto the tractor?
Raise the landing gear slightly, then pull the tractor gently forward while the trailer brakes are still locked
A gentle pull against the locked trailer brakes shows whether the connection holds.
Section 6 · Step 11: Check the Connection for Security ↗ -
Before going under the trailer to inspect the coupling, why do you take the key with you?
So someone else will not move the truck while you are under it
Put the transmission in neutral, apply the parking brakes, shut off the engine, and take the key.
Section 6 · Step 12: Secure the Vehicle ↗ -
After coupling, how much space should there be between the upper and lower fifth-wheel?
None
There must be no space between the upper and lower fifth-wheel.
Section 6 · Step 13: Inspect the Coupling ↗ -
You see space between the upper and lower fifth-wheel. What may be wrong?
The kingpin may be on top of the closed fifth-wheel jaws, and the trailer would come loose very easily
A gap means something is wrong with the coupling.
Section 6 · Step 13: Inspect the Coupling ↗ -
When you look into the back of the fifth-wheel from under the trailer, what must you see?
The jaws closed around the shank of the kingpin
The fifth-wheel jaws must have closed around the shank of the kingpin.
Section 6 · Step 13: Inspect the Coupling ↗ -
Where should the safety latch be after coupling?
In position over the locking lever
The locking lever is in the lock position with the safety latch over it. On some fifth-wheels the catch is put in place by hand.
Section 6 · Step 13: Inspect the Coupling ↗ -
The coupling is not right. What do you do?
Do not drive the coupled unit, and get it fixed
A bad coupling must be fixed before the unit is driven.
Section 6 · Step 13: Inspect the Coupling ↗ -
After plugging the electrical cord into the trailer, what do you fasten?
The safety catch
Plug in the cord and fasten the safety catch, then check the air and electrical lines for damage.
Section 6 · Step 14: Connect the Electrical Cord and ↗ -
What must the air and electrical lines not do?
Hit any moving parts of the vehicle
Make sure the lines will not hit moving parts.
Section 6 · Step 14: Connect the Electrical Cord and ↗ -
Which gear range do you use on the landing gear crank?
Low range to begin, then high range once the gear is free of weight
Start in the low gear range if there is one, and switch to high once the landing gear carries no weight.
Section 6 · Step 15: Raise the Front Trailer Supports ↗ -
Why must you never drive with the landing gear only part way up?
It may catch on railroad tracks or other things
Raise the landing gear all the way up before driving.
Section 6 · Step 15: Raise the Front Trailer Supports ↗ -
After raising the landing gear, what do you do with the crank handle?
Secure it safely
The crank handle is secured after the landing gear is raised.
Section 6 · Step 15: Raise the Front Trailer Supports ↗ -
With the full weight of the trailer on the tractor, where do you check for enough clearance?
Between the rear of the tractor frame and the landing gear, and between the tractor tires and the trailer nose
When the tractor turns sharply it must not hit the landing gear, and the tires must clear the trailer nose.
Section 6 · Step 15: Raise the Front Trailer Supports ↗ -
What is the last step of coupling a tractor-semitrailer?
Remove the trailer wheel chocks and store them in a safe place
The chocks come out last and are stored safely.
Section 6 · Step 16: Remove the Trailer Wheel Chocks ↗ -
When positioning the rig for uncoupling, what must the surface of the parking area be able to do?
Support the weight of the trailer
The ground must hold the trailer’s weight on its landing gear.
Section 6 · Step 1: Position the Rig ↗ -
Why should the tractor be lined up with the trailer for uncoupling?
Pulling out at an angle can damage the landing gear
Keep the tractor in line with the trailer so the landing gear is not damaged.
Section 6 · Step 1: Position the Rig ↗ -
How do you ease the pressure on the fifth-wheel locking jaws?
Shut off the trailer air supply to lock the trailer brakes, then back up gently
Backing gently against the locked trailer takes pressure off the jaws and helps release the locking lever.
Section 6 · Step 2: Ease the Pressure on the Locking ↗ -
When do you put the parking brakes on while easing pressure on the locking jaws?
While the tractor is pushing against the kingpin
Setting the parking brakes then holds the rig with the pressure off the locking jaws.
Section 6 · Step 2: Ease the Pressure on the Locking ↗ -
When uncoupling, in which case do you chock the trailer wheels?
If the trailer does not have spring brakes, or you are not sure
Air could leak out of the trailer tank and release its emergency brakes, so the trailer could move without chocks.
Section 6 · Step 3: Chock the Trailer Wheels ↗ -
The trailer is empty. How far do you lower the landing gear when uncoupling?
Until it makes firm contact with the ground
For an empty trailer, firm contact with the ground is enough.
Section 6 · Step 4: Lower the Landing Gear ↗ -
The trailer is loaded. After the landing gear makes firm contact with the ground, what do you do?
Turn the crank in low gear a few extra turns, without lifting the trailer off the fifth-wheel
A few extra turns lift some weight off the tractor, which makes it easier to unlatch the fifth-wheel and to couple next time.
Section 6 · Step 4: Lower the Landing Gear ↗ -
Where do you connect the air line glad hands after disconnecting them from the trailer?
To the dummy couplers at the back of the cab, or couple them together
The glad hands go on the dummy couplers or are coupled together, and the lines are supported so they are not damaged.
Section 6 · Step 5: Disconnect Air Lines and Electrical ↗ -
How do you hang the electrical cable after disconnecting it?
With the plug down, to prevent moisture from entering it
Hanging the cable plug down keeps moisture out.
Section 6 · Step 5: Disconnect Air Lines and Electrical ↗ -
What must you keep clear of when unlocking the fifth-wheel?
The rear tractor wheels, with your legs and feet
Keep legs and feet clear of the rear tractor wheels in case the vehicle moves.
Section 6 · Step 6: Unlock the Fifth-Wheel ↗ -
After the fifth-wheel comes out from under the trailer, where do you stop the tractor?
With the tractor frame still under the trailer
The frame under the trailer keeps it from falling to the ground if the landing gear collapses or sinks.
Section 6 · Step 7: Pull the Tractor Partially Clear of the ↗ -
What do you inspect before pulling the tractor fully clear of the trailer?
That the ground is supporting the trailer and the landing gear is not damaged
Check the trailer supports before driving the tractor clear.
Section 6 · Step 9: Inspect the Trailer Supports ↗ -
What do you check when inspecting a pintle hook before use?
Worn, damaged, or missing parts, and that the mount is secure
A pintle hook that is not secured to its mounting surface could separate from the vehicle.
Section 6 · Step 1: Inspect the Pintle Hook ↗ -
When coupling a pintle hook, where do you position the drawbar eye?
Over the horn of the pintle hook, then lower it into place
The drawbar eye is lowered onto the horn of the pintle hook.
Section 6 · Step 3: Lower the Drawbar Into Place ↗ -
How can you tell that a pintle hook latch is correctly locked?
The lock handle rotates and moves up until it is flush with the top of the latch
When the latch is pushed closed and locked, the lock handle sits flush with the top of the latch.
Section 6 · Step 4: Lock the Pintle Hook ↗ -
What can result from failing to lock the pintle hook latch correctly?
Separation of the trailer and vehicle
An unlocked latch can let the trailer separate, which could cause death or serious injury.
Section 6 · Step 4: Lock the Pintle Hook ↗ -
Where do you park the trailer to uncouple a pintle hook?
On a firm level surface, with the trailer tires blocked
Park on a firm level surface and block the trailer tires.
Section 6 · Step 1: Park on a Level Surface ↗ -
Which of these do you disconnect when uncoupling a pintle hook trailer?
The electrical connector, the breakaway brake switch lanyard, and the safety chains
The electrical connector, breakaway switch lanyard, and safety chains are disconnected from the tow vehicle.
Section 6 · Step 2: Disconnect the Electrical Connector, ↗ -
Before extending the trailer jack, what do you make certain of?
That the ground below the jack pad will support the tongue load
The ground under the jack pad must be able to carry the tongue load.
Section 6 · Step 4: Check the Ground Surface for ↗ -
When coupling a drawbar, how far do you turn the adjustment screw outwards?
At least 5 turns
After loosening the safety lock screw, the adjustment screw is turned outwards at least 5 turns.
Section 6 · 6.4.5 – Coupling a Drawbar ↗ -
To what torque are the drawbar lock screws and their self-locking nuts tightened?
350 to 400 newton meters
Both lock screws are tightened to 350 to 400 Nm with a torque wrench.
Section 6 · Step 4: Rotate the Safety Cover Bar ↗ -
The safety cover bar of a drawbar coupling will not lodge properly into its seating. What follows?
Travel is strictly forbidden
If the safety cover bar does not seat perfectly, you must not travel.
Section 6 · 6.4.5 – Coupling a Drawbar ↗ -
What is the first step in uncoupling a drawbar?
Make sure that the trailer brake is on
Uncoupling a drawbar begins with the trailer brake on.
Section 6 · Step 1: Turn the Trailer Brake On ↗ -
What do you make sure of about the gooseneck ball before coupling?
That it is properly lubricated
Open the clamp latch on the coupler and make sure the gooseneck ball is properly lubricated.
Section 6 · Step 1: Open the Latch and Lubricate the ↗ -
What does the law require all trailers to have?
Safety chains
All trailers are required by law to have safety chains, so attach them.
Section 6 · Step 3: Attach the Safety Chains ↗ -
After connecting the trailer light wiring on a gooseneck trailer, what do you check?
All of your lights, including your brake lights
Check every light, brake lights included.
Section 6 · Step 4: Connect the Trailer Light Wiring ↗ -
What do you do with the trailer jacks at the end of coupling a gooseneck hitch?
Completely lower and stow them, letting the weight settle onto the tow vehicle
The jacks are lowered and stowed so the tow vehicle carries the weight.
Section 6 · Step 5: Lower and Stow the Trailer Jacks ↗ -
What is the first step in uncoupling a gooseneck hitch?
Remove the safety pin and clip
The safety pin and clip come out first. Then the handle is rotated and the trailer raised off the ball.
Section 6 · 6.4.8 – Uncoupling a Gooseneck Hitch ↗
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