This is a diagram of an “S-cam Air Brake.  When a driver pushes on the brake pedal, air is let into each brake chamber.  The Air pressure pushed the rod out which ultimately twists the brake camshaft.  The force moves the brake shoes away form one another and presses them against the inside of the brake drum. 

  

Tractor Trailer Brakes


Our attorneys, investigators, accident reconstructionist, and trucking safety experts will assess the braking system(s) of the truck involved. Faulty brakes are often are the platform of our negligence case against the truck driver and motor carrier.

 

There have been thousands of trucking injury accidents that involve defective brakes and often it is because the motor carrier, service garage or the driver have not inspected or repaired the brakes appropriately.

 

Call attorney Jason Waechter of www.TruckAccidentLawyers-USA.com.  Our associating attorneys in each state specialize in handling injury accidents involving tractor trailers (semi trucks). Call now for free advice.  Often, time is of the essence and quick thorough investigation makes the difference in these specialized cases. Call and speak to Attorney Jason Waechter personally at:

 

1-800-708-5433.

 

INFORMATION

Semi truck brakes systems are different from most car brakes.  Big trucks use air pressure instead of hydraulic fluid, to trigger the brakes since there is a greater braking force needed. 

 

Air pressure systems make the coupling and uncoupling of trailers from the tractor (cab) unit easier and it reduces the potential for problems typical to hydraulic systems (leakage or brake failure caused when overheated brake fluid vaporizes in the hydraulic lines).

 

A spring brake system is used on a tractor’s "parking brake" as well as on the "emergency brakes" of the trailer.  Spring brakes require air pressure in order to be released. They are applied when air pressure is released from the system, and disengaged when air pressure is supplied. This is an emergency type feature that makes sure that if air pressure to the cab/tractor or the trailer is lost, there will be some braking capacity.

 

THREE SEPARATE BRAKES

Air brakes use compressed air to make the brakes work. Air brakes are a good and safe way of stopping large and heavy trucks, but the brakes must be well maintained and used properly. Air brakes system really includes three different brakes: service brake, parking brake, and emergency brake.

  • The service brake system applies and releases the brakes when you use the brake pedal during normal driving.
  • The parking brake system applies and releases the parking brakes when you use the parking brake control.
  • The emergency brake system uses parts of the service and parking brake systems to stop the vehicle in a brake system failure.

The trailer controls are coupled to the tractor through Two "glad-hand" connectors are connected between the trailer and the tractor which provide air pressure and electrical supply. "Glad-hand" connectors are also known as "palm couplings," are merely air hose connectors.  There typically is an "emergency" or main air supply line pressurizes the trailer's air tank and disengages the emergency brake, and a second line called a “service” line controls the brake application.

 

STUDIES SHOW BRAKE FAILURE/DEFECTS A MAJOR CAUSE IN HIGH PERCENTAGE OF CRASHES

In 2004 the National Highway Traffic Safety Administration (NHTSA) reported over 400,000 big trucks were involved in traffic crashes in the U.S. and that 5,190 people died and an additional 116,000 were injured in those crashes. One out of eight traffic fatalities in 2004 resulted from a collision involving a large truck.


In a popular report by Jones I. and H. Stein called Defective Equipment and Tractor-Trailer Crash Involvement. Accident Analysis and Prevention 21:469-81, 1989), Jones & Stein found that brake defects were quite common and were found in 56% of the tractor-trailers involved in these crashes.

 

There are standards for original equipment (OE) brakes.  The large truck brakes must comply with federal motor vehicle safety standards which specify maximum stopping distances according to vehicle weight, loading, pedal effort -- with and without power assistance-- and brake condition.  It should be noted that there are no federal performance standards for aftermarket (AM) brake linings. This is something an attorney or expert involved in a case should investigate.

 

Also the National Highway Traffic Safety Administration implemented a rule requiring antilock brakes for heavy trucks, tractors, trailers, and buses. All new truck tractors were required to have antilock brakes after March 1, 1997.  Further, they were mandatory on new air-braked trailers and single-unit trucks and buses after March 1, 1998. New single-unit trucks and buses with hydraulic brakes had to be equipped with antilocks after March 1, 1999.

 

JACKKNIFING

Antilock brakes not only reduce stopping distances on wet and slippery roads but also help drivers maintain control.  Tractor-trailer combinations also have the potential for loss of control and jackknifing on both dry and, especially, slippery roads. Trucks Jackknife when the rear wheels of a tractor lock up, allowing the tractor to skid and spin so that it folds into the trailer. Jackknifing also may happen when trailer wheels lock-up and cause the trailer to swing around the tractor.  For semi-trailers, at least one axle must have antilock brakes. Full trailers must have antilock brakes for at least one front and one rear axle.

 

FEDERAL LAW:
From the FMCSA.DOT.GOV website on brakes
Subpart C—Brakes
§393.48 Brakes to be operative.


(a) General rule. Except as provided in paragraphs (b), (c), and (d) of this section, all brakes with which a motor vehicle is equipped must at all times be capable of operating.


(b) Devices to reduce or remove front-wheel braking effort. A commercial motor vehicle may be equipped with a device to reduce the front wheel braking effort (or in the case of a three-axle truck or truck tractor manufactured before March 1, 1975, a device to remove the front-wheel braking effort) if that device meets the applicable requirements of paragraphs (b)(1) and (2) of this section.


(b)(1) Manually operated devices. Manually operated devices to reduce or remove front-wheel braking effort may only be used on buses, trucks, and truck tractors manufactured before March 1, 1975. Such devices must not be used unless the vehicle is being operated under adverse conditions such as wet, snowy, or icy roads.


(b)(2) Automatic devices. Automatic devices must not reduce the front-wheel braking force by more than 50 percent of the braking force available when the automatic device is disconnected (regardless of whether or not an antilock system failure has occurred on any axle). The device must not be operable by the driver except upon application of the control that activates the braking system. The device must not be operable when the brake control application pressure exceeds 85 psig (for vehicles equipped with air brakes) or 85 percent of the maximum system pressure (for vehicles which are not equipped with air brakes).


(c) Exception. Paragraph (a) of this section does not apply to—


(c)(1) A towed vehicle with disabling damage as defined in §390.5;


(c)(2) A vehicle which is towed in a drive-away/tow-away operation and is included in the exemption to the requirement for brakes on all wheels, §393.42(b);


(c)(3) Unladen converter dollies with a gross weight of 1,361 kg (3,000 lbs) or less, and manufactured prior to March 1, 1998;


(c)(4) The steering axle of a three-axle dolly which is steered by a co-driver;


(c)(5) Loaded house moving dollies, specialized trailers and dollies used to transport industrial furnaces, reactors, and similar motor vehicles provided the speed at which the combination of vehicles will be operated does not exceed 32 km/hour (20 mph) and brakes on the combination of vehicles are capable of stopping the combination within 12.2 meters (40 feet) from the speed at which the vehicle is being operated or 32 km/hour (20 mph), whichever is less.


(c)(6) Raised lift axles. Brakes on lift axles need not be capable of being operated while the lift axle is raised. However, brakes on lift axles must be capable of being applied whenever the lift axle is lowered and the tires contact the roadway.


(d) Surge brakes. (1) Surge brakes are allowed on:


(d)(1)(i) Any trailer with a gross vehicle weight rating (GVWR) of 12,000 pounds or less, when its GVWR does not exceed 1.75 times the GVWR of the towing vehicle; and


(d)(1)(ii) Any trailer with a GVWR greater than 12,000 pounds, but less than 20,001 pounds, when its GVWR does not exceed 1.25 times the GVWR of the towing vehicle.


(d)(2) The gross vehicle weight (GVW) of a trailer equipped with surge brakes may be used instead of its GVWR to calculate compliance with the weight ratios specified in paragraph (d)(1) of this section when the trailer manufacturer’s GVWR label is missing.


(d)(3) The GVW of a trailer equipped with surge brakes must be used to calculate compliance with the weight ratios specified in paragraph (d)(1) of this section when the trailer’s GVW exceeds its GVWR.


(d)(4) The surge brakes must meet the requirements of §393.40.


[39 FR 26907, July 24, 1974, as amended at 41 FR 29130, July 15, 1976; 41 FR 53031, Dec. 3, 1976; 70 FR 48051, Aug. 15, 2005; 72 FR 9870, March 6, 2007]
 

From the FMCSA.DOT.GOV website on Antilock brakes:
A. What is an ABS?

Antilock braking systems (ABS's) are electronic systems that monitor and control wheel slip during vehicle braking. ABS's
can improve vehicle control during braking, and reduce stopping distances on slippery (split or low coefficient of friction) road surfaces by limiting wheel slip and minimizing lockup. Rolling wheels have much more traction than locked wheels. Reducing wheel slip improves vehicle stability and control during braking, since stability increases as wheel slip decreases.

 

ABS's can be applied to nearly all types of vehicles and can be successfully integrated into hydraulic and air brake systems
(including air over hydraulic). This document applies to the ABS's used with air brake systems on commercial vehicles.

 

The National Highway Traffic Safety Administration (NHTSA) requires—through FMVSS 121, “Air Brake Systems” and FMVSS 105,

 “Hydraulic Brake Systems”—that ABS's be installed on commercial vehicles built (built meaning the official date of manufacture) on or after:

  • March 1, 1997, for air-braked truck-tractors.
  • March 1, 1998, for other air-braked vehicles (trucks, buses, trailers and converter dollies).
  • March 1, 1999, for hydraulically braked trucks and buses with gross vehicle weight ratings of more than 10,000 lbs.

The equipment requirements of FMVSS 121 specify that ABS's on truck-tractors and full trailers must control the brake
pressures to at least one front axle and one rear axle. The ABS's on semi-trailers and dollies must control at least one axle of the vehicle. Additionally, the ABSs on tractors must control one of the rear axles with two modulator valves so that the brake pressure on one end of the axle is independent of the brake pressure on the other end. The performance requirements of FMVSS 121 can require an ABS on additional axles.

 

NHTSA defines an ABS as a portion of a service brake system that automatically controls the degree of rotational wheel slip during braking by:

  • Sensing the rate of angular wheel rotation.
  • Transmitting signals regarding the rate of wheel rotation to one or more devices, which interpret these signals and generate responsive controlling output signals.
  • Transmitting those signals to one or more devices which adjust braking forces in response to the signals.

Other aspects of NHTSA’s rule stipulate that:

  • ABS's on trailers must be capable of being powered by the trailer’s stop lamp circuit.
  • New tractors—built on or after March 1, 1997— provide constant electrical power to a tractor-to-trailer electrical connector for powering trailer ABS's.
  • Vehicles required to have an ABS also have a yellow ABS malfunction indicator lamp which lights up to indicate most malfunctions.
  • The power unit’s ABS malfunction lamp be “in front of and in clear view” of the driver. It lights when the ignition key is first switched “on” for a bulb check.
  • The ABS malfunction lamp on trailers be mounted on the left side of the trailer, near the rear side marker lamp. On dollies, the lamp is located on the left side where it can be seen by someone standing about 10 feet from the lamp. The lamp lights for a short bulb check when the vehicle is stopped and the ABS starts receiving electrical power. This lamp will no longer be required after February 2009.
  • Air-braked tractors and trucks which tow other air-braked vehicles—built on or after March 1, 2001— have an in-cab warning lamp which indicates malfunctions in any towed trailer’s or dolly’s ABS. Its location and function are the same as for the powered unit’s ABS malfunction lamp.
  • Trailer and dolly ABS's—built on or after March 1, 2001—have the equipment needed to send an ABS malfunction signal to the towing vehicle. A towing trailer must also be able to relay an ABS malfunction signal from the vehicle it is towing to the vehicle towing it.

B. How Do ABS's Work?
An ABS consists of several key components: electronic control unit (ECU), wheel speed sensors, modulator valves, and
exciter rings. Here’s how these components work together:


1. Wheel speed sensors constantly monitor and send electrical pulses to the ECU at a rate proportional to the wheel speed.


2. When the pulse rates indicate impending wheel lockup, the ECU signals the modulator valve(s) to reduce and/or hold the brake application pressure to the wheel(s) in question.


3. The ECU then adjusts pressure, seeking one which gives maximum braking without risking wheel lockup.


4. When the ECU acts to modulate the brake pressure, it will also (on most vehicles) turn off the retarder (if so
equipped) until the risk of lockup is over.


5. The ECU continually checks itself for proper operation. If it detects a malfunction/failure in the electrical/electronic system, it will shut down that part of the ABS affected by the problem—or the entire ABS—depending upon the system and the problem. When this happens, the ABS malfunction lamp lights up.

 

An ABS adjusts brake pressure much faster and more accurately than can drivers. It’s faster because:

  • Electronic controls are very fast and
  • ABS modulator valves are physically closer to the brakes than is the driver’s foot brake valve.

It is more effective, too, because an ABS can tailor the brake pressure to each wheel or set of wheels to provide maximum
braking/stability. Some vehicles also use a traction control system in conjunction with the ABS. Traction control helps the
ABS improve vehicle traction by minimizing wheel slip on the drive axle during acceleration. If a wheel on the drive axle starts to slip, the traction control system automatically brakes the wheel slightly, transferring engine torque to the wheels with better traction. If all the drive wheels start to slip, the traction control system may also reduce engine power.

 

Traction control systems are referred to by several different names, depending on the manufacturer. These include:

  • Automatic Traction Control (ATC)
  • Traction Control (TC)
  • Automatic Slip Regulation/Anti-Spin Regulation (ASR) Our attorneys, investigators, accident reconstructionist, and trucking safety experts will assess the braking system(s) of the truck involved. Faulty brakes are often are the platform of our negligence case against the truck driver and motor carrier.

There have been thousands of trucking injury accidents that involve defective brakes and often it is because the motor carrier, service garage or the driver have not inspected or repaired the brakes appropriately.

 

Call attorney Jason Waechter of www.TruckAccidentLawyers-USA.com.  Our associating attorneys in each state specialize in handling injury accidents involving tractor trailers (semi trucks). Call now for free advice.  Often, time is of the essence and quick thorough investigation makes the difference in these specialized cases. Call and speak to Attorney Jason Waechter personally at: 1-800-708-5433.