Questions on Real Exam
20
Combination Vehicles — DL-7C
Minimum to Pass
16 Correct
80% passing threshold
Practice Questions
30
Full module coverage
Test Order
Step 4 of 4
After Special Requirements
Quick Reference — Texas DL-7C
Handbook Section
DL-7C Section 6
Real Exam Questions
20 questions
Minimum to Pass
16 correct (80%)
Practice Questions
30 questions
Supply Line Color
Red — emergency/supply
Service Line Color
Blue — service brakes
The Combination Vehicles test is required for a Class A CDL. It covers Section 6 of the DL-7C. The most heavily tested topics are coupling and uncoupling procedure (including the tug test), glad hand color coding (red = supply/emergency, blue = service), rollover prevention, jackknife causes and corrections, and off-tracking during turns. Study these topics first.
What the Texas CDL Combination Vehicles Test Covers
The real Texas CDL Combination Vehicles exam has 20 questions, and you need 16 correct (80%) to pass. Topics tested include:
- Coupling and uncoupling
- Off-tracking
- Jackknife and rollover prevention
- Air line connections
- Vehicle inspection for combination vehicles
Filter:
Texas CDL Combination Vehicles Practice Questions
Texas CDL Combination Vehicles — Complete Study Guide
The Combination Vehicles test is required for a Class A CDL and covers Section 6 of the Texas CDL Handbook (DL-7C). A Class A CDL is required to operate any combination vehicle with a Gross Combination Weight Rating of 26,001 pounds or more, where the vehicle being towed has a GVWR exceeding 10,000 pounds. This covers tractor-trailers, truck and full trailer combinations, and similar large combination vehicles. The real exam has 20 questions — you need 16 correct (80%) to pass.
Most Tested Combination Topics: The tug test after coupling, glad hand color coding (red supply vs blue service), what causes each type of jackknife (tractor vs trailer), the rollover prevention rule (reduce speed BEFORE the curve), and trailer off-tracking during right turns appear on nearly every Texas Combination Vehicles exam.
Key Topics Covered
- Coupling Procedure — First step: always inspect the fifth wheel area before backing under. Back slowly, check coupling height, connect air lines (red supply first, then blue service), raise landing gear, perform tug test, inspect coupling. The tug test — gently pulling forward with trailer brakes applied — is the definitive security confirmation.
- Uncoupling Procedure — Lower landing gear until it supports the trailer, apply trailer spring brakes (red octagon), release fifth wheel, disconnect air lines and electrical, pull tractor forward slowly. Never release the fifth wheel before landing gear is down and trailer brakes are applied.
- Air Lines and Glad Hands — Red emergency/supply line: supplies air to trailer tanks, holds spring brakes released. Blue service line: carries brake signal from foot valve during stops. Never cross the lines — crossed connections cause dangerous brake malfunctions. Glad hand seals must be clean and intact.
- Rollover Prevention — Speed is the single greatest rollover factor. Reduce speed before curves — never brake inside a curve. Rollover risk increases with the square of speed. Loaded tankers and top-heavy loads have lower rollover thresholds than posted curve advisory speeds. Never make sudden lane changes at highway speed with a loaded trailer.
- Jackknife Prevention — Tractor — A tractor jackknife occurs when drive wheels lock up, causing the rear of the tractor to slide sideways toward the trailer. Prevention: avoid hard braking especially on slippery roads, use ABS correctly. If a tractor jackknife begins, immediately release all brakes to allow drive wheels to roll and regain traction.
- Jackknife Prevention — Trailer — A trailer jackknife occurs when trailer wheels lock up and the trailer swings outward. More likely with empty or lightly loaded trailers (less axle weight = less traction). Prevention: avoid locking trailer brakes, especially with light loads. Trailer ABS specifically prevents this.
- Off-Tracking — Rear trailer wheels follow a shorter, tighter arc than the tractor front wheels during turns. The longer the trailer, the greater the off-tracking. Compensation: swing wide LEFT before turning right. Watch rear trailer mirrors throughout all turns. Never allow vehicles or pedestrians between you and the curb when setting up for a right turn.
- Fifth Wheel Inspection — Check: no gap between tractor and trailer plates, fifth wheel jaws fully closed around kingpin, release handle locked, mounting bolts present and tight. A cracked fifth wheel is an immediate out-of-service defect — the fifth wheel bears the entire trailer load.
Key Numbers to Know
20
Questions on real exam
16
Correct to pass (80%)
30
Practice questions here
Red
Supply/emergency line color
Blue
Service line color
2 in
Standard kingpin diameter
Tug
Test confirms coupling
Left
Swing before right turn
Speed
#1 rollover factor
Release
Brakes to stop jackknife
14 days
Min CLP hold before skills
80%
Passing threshold
Frequently Asked Questions
What does the Texas CDL Combination Vehicles test cover?
The Combination Vehicles test covers coupling and uncoupling procedures, fifth wheel inspection, glad hand air line connections (red supply vs blue service), rollover prevention, jackknife causes and prevention, off-tracking during turns, trailer air brake systems in combination vehicles, and combination vehicle pre-trip inspection. It is based on Section 6 of the Texas DL-7C handbook.
What is the tug test and why is it important?
The tug test is performed after coupling to confirm the fifth wheel has properly locked around the kingpin. With trailer spring brakes applied and tractor spring brakes released, gently pull forward. If the trailer does not move, the coupling is secure. If the trailer moves, the fifth wheel did not engage and the coupling must be redone before driving.
What are glad hands and why does color matter?
Glad hands are the coupling devices connecting tractor air hoses to trailer air lines. The RED line is the emergency/supply line — it supplies air to the trailer tanks and holds the trailer spring brakes released. The BLUE line is the service line — it carries the brake signal from the foot pedal during stops. Crossing the lines creates dangerous brake malfunctions and must never be done.
What causes a tractor jackknife vs a trailer jackknife?
A TRACTOR jackknife is caused by the drive wheels of the tractor locking up, causing the rear of the tractor to slide sideways toward the trailer. Correction: immediately release all brakes. A TRAILER jackknife is caused by trailer wheels locking up, causing the trailer to swing outward. More common with empty trailers (less traction). Correction: release brake pressure immediately to allow trailer wheels to roll.
How does off-tracking work in a Texas tractor-trailer turn?
Off-tracking occurs because the rear axles of the trailer must follow a shorter, tighter arc than the front wheels of the tractor during turns. The rear trailer wheels cut toward the inside of the turn. During a right turn, the trailer rear wheels can hit the curb, pedestrians, or other vehicles. Compensation: swing wide to the left before turning right, then monitor rear trailer mirrors throughout the entire turn.