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Most tractor-trailers use compressed air to operate their brakes. Air pressure activates brake chambers, which apply force to drum or disc brakes at the wheels. Safe stopping also depends on the trailer brakes and proper maintenance.
When a truck driver says the brakes failed, that explanation needs to be tested. Was a part defective? Had the company ignored a reported problem? Did speed, following distance, or driver actions contribute? Those questions matter after someone is seriously hurt.
I am Greg Baumgartner. I have handled more than 100 commercial vehicle accident cases during more than 40 years representing injured people. When equipment failure is suspected, I want the truck’s condition and the maintenance records examined together. Either one can leave important questions unanswered.
On this page
How air brakes work | Service parking and emergency brakes | What ABS does | Stopping distance and brake problems | Maintenance duties | Evidence after a crash | Our experience and results | Frequently asked questions
An air compressor fills storage tanks with compressed air. When the driver presses the foot brake, control valves direct air to brake chambers. The chambers turn air pressure into mechanical force at the wheels. Releasing the pedal releases the service brake application.
The tractor and trailer have connected air systems, but their components must be examined separately. A problem on one part of the combination may affect how the entire vehicle stops.
| Part | What it does |
| Air compressor and reservoirs | Build and store the compressed air used by the system. |
| Foot valve and air lines | Control and carry air pressure when the driver applies the service brakes. |
| Brake chambers and linkage | Turn air pressure into the force that applies the wheel brakes. |
| Drums or rotors and friction material | Create the friction that slows the wheels. |
| Pressure gauges and warning devices | Help alert the driver to pressure loss or other system problems. |
Air describes how force reaches the brakes. Drum and disc describe the brake design at the wheel. Both designs can be operated by air.
In a drum brake, shoes with friction linings press against the inside of a rotating drum. In a disc brake, pads clamp against a rotating rotor. Both create heat as they slow the vehicle. The correct inspection depends on the equipment installed on that truck and trailer.
The service brakes provide normal stopping and speed control through the foot pedal. On a tractor-trailer, the driver’s normal brake application controls braking on both the tractor and the connected trailer.
Many heavy trucks use powerful springs to apply the parking brakes. Air pressure holds those springs back while the vehicle operates. Releasing that pressure allows the springs to apply the brakes.
That distinction matters: compressed air applies the service brakes, while releasing air allows the spring parking brakes to apply. The same brake parts at the wheels may serve both functions.
Emergency features may use parts of the service and parking brake systems. Spring brakes can apply automatically when air pressure falls far enough. Their effectiveness still depends on the condition and adjustment of the brake components.
These features do not guarantee a controlled stop after every failure. The federal commercial vehicle brake requirements address service, parking, emergency, and trailer breakaway braking, with requirements that vary by vehicle and equipment.
Antilock braking systems, or ABS, monitor wheel speed and adjust brake pressure to reduce wheel lockup during braking. This can help a driver maintain steering control. ABS does not repair worn brakes or make every stopping distance shorter.
The federal ABS requirements in Section 393.55 depend on vehicle type and manufacture date. For example, the air-braked tractor requirement generally begins March 1, 1997; the requirement for other air-braked commercial vehicles generally begins March 1, 1998, subject to exceptions.
An ABS warning light is a reason to investigate the system. It does not, by itself, establish that all braking was lost or that an ABS problem caused the crash.
A truck needs distance while the driver recognizes a hazard and reacts. Air brakes also have a brief application delay called brake lag. The vehicle then needs additional distance to slow and stop. Speed, cargo, road grade, tire traction, weather, and brake condition affect the result.
There is no reliable rule that every semi takes exactly one-third longer to stop than a passenger car. In a disputed crash, an expert may need to evaluate the actual speed, load, road, and braking evidence.
Brake fade can develop when excessive heat reduces braking effectiveness. If some brakes are not doing their share, the remaining brakes may have to work harder and overheat.
A driver’s statement that the truck “would not stop” may involve several causes. Our truck brake failure accident practice addresses how a suspected defect can affect an injury claim.
For vehicles subject to the federal rules, Section 396.3 requires systematic inspection, repair, and maintenance. The carrier must keep safety-related parts in proper operating condition and maintain the required records.
The driver also has duties before driving. Under Section 396.13 on driver inspections, the driver must be satisfied that the vehicle is safe and review the last inspection report when required.
A repair invoice, an inspection sticker, and a driver’s account each provide part of the picture. I want to know what problem was reported, what work was done, whether it was checked, and what happened when the truck returned to service.
Depending on the evidence, responsibility may involve the carrier, driver, maintenance contractor, or a company that supplied a defective part. Our page about claims involving poor truck maintenance explains the maintenance issues in more detail.
The first question is whether a problem existed before impact. A damaged brake hose found after a collision may have contributed to the crash, or it may have been damaged by the crash itself. An inspection should address that difference.
When the facts support a brake investigation, useful evidence may include:
Our guide to electronic truck data after a collision explains what some systems may record. A brake application signal may help show when the driver reacted. It does not necessarily show that every wheel brake produced the expected stopping force.
My approach is to compare the physical condition with the records and the sequence of events. A violation may be important, but the evidence still needs to show how the problem contributed to the collision or the harm.
Early preservation requests can help identify the truck, trailer, removed parts, and records that should be kept. An inspection may need to occur before repairs or disposal change the evidence. Further legal steps may be necessary; a letter alone does not ensure that everything will be preserved.
Baumgartner Law Firm handles a limited number of serious injury and wrongful death cases so I can remain personally involved. That includes evaluating the crash evidence and the medical proof needed to explain what the client has lost.
The care needs following serious truck crash injuries can extend long beyond the first hospital stay. Families dealing with a fatal commercial truck accident also need advice about preserving evidence and evaluating the available claims.
Our published truck case results include a $3.74 million recovery involving a head injury and a $3 million recovery involving a neck injury requiring surgery. These are examples of our broader truck accident work. The gross recoveries were subject to attorney fees and expenses: $1.7 million and $109,000 in the first case, and $1 million and $55,450 in the second.
Read more about our commercial truck case results. Past results do not guarantee a similar outcome. Each claim depends on its evidence, injuries, coverage, and other facts.
They can use both. Air pressure supplies the force to operate the brakes. Disc and drum refer to the design that creates friction at the wheel. Both designs are used on heavy trucks.
A pressure problem can affect braking, and spring brakes may apply as pressure falls. The outcome depends on the system, the nature of the failure, and the condition of the components. It is unsafe to assume that spring brakes will always stop the truck smoothly.
No. ABS can reduce wheel lockup and help maintain control, but it cannot overcome every combination of speed, road conditions, loading, driver actions, and equipment problems.
No. Late braking, distraction, following too closely, road conditions, or mechanical defects may be involved. The physical evidence and records need to be examined before identifying the cause.
Possibly. A failure described as sudden may follow an earlier warning or missed maintenance. The investigation should determine whether the problem could reasonably have been found or prevented and whether it contributed to the crash.
If you were seriously hurt and suspect a braking problem, our Texas truck accident law firm can discuss the evidence that may need attention. You do not need to know the exact mechanical defect before asking for advice.
Call (281) 893-0760 or request a free consultation. We charge no attorney’s fee unless we recover compensation for you.
