Truck Crash: Foundation Air Brake Fade; Scott L Turner

Truck Crash: Foundation Air Brake Fade; Scott L. Turner

Air brake mechanical failure is not a common event, in-fact, it is very uncommon; however, mechanical things do break from time to time.

If brake failure does occur, it is often due to maintenance failures of the motor carrier, although this is not always the causation of brake failure. There are also the driver components as to how he uses his/her braking system, or abuse of the braking system. 

I write this post from the perspective of one who has personally responded to over 1,000 truck crashes, many as a result of the inability to effectively stop and 80,000 GVWR commercial motor vehicle (CMV), at times as a result of not creating enough space cushion, or another vehicle attepting to occupy the same space as the CMV whereas the CMV can not stop quickly enough. In addition, as a former driver of a CMV in my earlier years, I too nearly lost my life as a result of brake failure in the mid-1980’s.

I don’t say that God was my co-pilot; he simply took the wheel.

Around 1986 I was on Route 100 in Vermont, headed to New Hampshire. My load consisted of a gross total of 90,000# plus load on a lowboy, or dropdeck type trailer, a heavy machinery transport unit. The load was a very large Komatsu track-hoe excavator that I was contracted to transport..

I picked the machine up at the piers at Port Newark, New Jersey as the machine was in-bound from Japan. After picking up the 10’4” wide-load, I intended to take the New York State Thruway to the Massachusetts Turnpike, then onto New Hampshire. When I reached the entry way for the Massachusetts Turnpike, it was temporarily restricted to wide-loads due to construction. I had to re-route.

Little did I know that my new route would take me through the ski regions of Vermont, I was in my early 20’s and was not very well traveled in the Northeast.

Driving an early model, owned and operated Mack R-600 with a five speed transmission, I was traveling up and down these seemingly harmless hills; until, there it was! Staring me in the face like a death sentence, a walk down that so-called “green mile”, and I had done nothing wrong; or so I thought………. Ignorance was my only crime.

Apparently, the signage that stated “trucks use low gears, 5 mile mountain, ?% grade” had been knocked down previously by an auto colliding with it as a result of a previous snow event, according to a State Trooper. But this I can say, it was steep, long and quite frankly “horrifying”..

At the crest of the mountain I was in fifth gear, at approximately 45 MPH. Suddenly I looked down the throat of this seemingly endless two lane mountain roadway, I immediately knew I was in trouble.

My truck immediately began picking up speed; I contemplated jumping out for a split second as there were no dwellings, only woods. Not a good idea. So I grabbed the wheel, starting speaking loudly to the Good Lord to save me from this inevitable crash, return me home to my wife and newborn son.

I tried to downshift in a panic, missed my gear to 4^th, and then could not get it back into 5^th. I was freewheeling out of control with a speed quickly beyond that of the 100 MPH mark; although my speedometer pinned out at 80 something way before that.    

While only grabbing the steering wheel, I tried to slow my CMV by braking, then I had to try and fan my brakes because I had no choice, that was all I had left.

I quickly viewed my air gauges to only watch my pressure rapidly decline as I was quickly approaching 80 PSI and below. Then it happened, both of my dash air brake buttons popped; my yellow parking brake and red trailer air supply buttons both. Now I am in a total free wheel in excess of 100 MPH with no brakes.

Near instantly I saw smoke coming from my brake assembly areas of my trailer tires and tractor tires; from smoke to quickly what appeared to be fire(s). This was the least of my concerns at this point.

When smoke begins to emanate from a foundation air brake structure, the temperature is in-excess of 850 degrees Fahrenheit. If you are following a CMV and smell brake burn, the drum and shoe friction material temperature has exceeded 550 degrees Fahrenheit. This data is according to Carlisle Brake and Friction.

I blew through this little town at the bottom of the five mile mountain at over 100 MPH, using what little air I had left to warn the town folks that a freight-train was coming down the mountain, uncontrollably without tracks or brakes.

Thank God the towns folks were either keen to this type occurrence, or there were just too few residence to by chance be in the street.

A long story short; it took me several miles to finally come to a stop with my trailer tires fully engulfed in flames and my tractor tires smoking like the Marlboro Man after a six pack on a Friday night.

I know this reads more like a novel than an educational or informative post to my blog; however, in addition to other issues such as routing, pre-planning trips, maintenance, etc., there is a relative moral to this story: brake fade is serious business often with deadly consequences.

I will not get to technical in this post as to how brakes work and how they fail with exception to a degree of brake fade issues.

There are several different types of brake fade; but first one needs to understand how CMV airbrakes actually work, in general terms.

Below is a diagram that demonstrates as to how specifically an airbrake system works:

                                                                                  Source: © 2008 HowStuffWorks

In simplistic and layperson terms, air is converted to mechanical energy. When the driver pushes down onto his brake treadle (foot valve), this sends air to the brake chambers, which in turn the air is converted to mechanical energy by pushing out the pushrod. The pushrod is attached by a clevis pin to an automatic slack adjuster. The slack adjuster is connected to a camshaft. The camshaft rotates on the rotation of the slack adjuster by means of the pushrod being exerted outward from the brake chamber.

At the drum side of the camshaft there is an “S” design (hence: S-Camshaft) which rotates and mechanically expands the brake shoes (friction material) against the inner drum, thereby creating friction and causing the truck to slow down or stop.

There are many factors as to foundation airbrake performance; as such, I have listed just a few, without getting into the air supply itself, or extensive potential list of driver error factors:

Direct Human Factors:

• What does the ECM data tell us, if available?
• Was the brake application a hard brake application?
• What was the speed just prior to the hard brake application, through to the crash? 
• Where there any distractions causing delayed reaction?
• Perception to reaction time considerations

Direct Mechanical Factors:

• Were the pushrod strokes such that the braking ability is substantially reduced due to pushrods being out-of-adjustment?
• How much friction material was on the shoes at the time of the crash?
• Were there any wheel/drums that were in violation whereas the drum friction contact points were grease coated?
• Were the inner drums (friction points) rusted? If so, it likely indicates an inactive brake?
• Was there more than 20% of the total brakes out-of-adjustment, or other mechanical malfunction(s)?
• Was there a misalignment of the brake linings?
• Foundation airbrake lag time consideration

Other Factors:

• Improper weight distribution of cargo
• Cargo-tank product surge factors
• Were the tires not maintained with proper inflation?
• Road surface conditions.
• Weather conditions.

Brake fade that caused my brake shoes and drums to brake glazing was ultimately a major contributor to causation of my runaway truck back in approximately 1986.

Brake fade was initially caused by the excessive overheating of my brake drums. As my brake drums overheated due to excessive friction material pressing excessively against the drums, the drums essentially expanded beyond the point of effective usefulness as a result of the 850 plus degrees Fahrenheit that was generated.

In sense, when the brake drums overheated to the point of excessive expansion, the brake shoe friction material becomes less in contact with the brake drum as the drum pulls away from the brake shoes. The brake drum, round in shape actually expands in its circumference.  

As the CMV picked up speed, the situation only deteriorated more rapidly. When both of my dash air brake buttons popped; my yellow parking brake and red trailer air supply button, the brake shoes pushed excessively against the brake drum causing an instant brake glaze.

You know the rest of the story.

Foundation air brake fade is essentially assigned to one or more brake fade conditions, they are as follows: mechanical fade, friction fade, fluid fade, and domino effect fade.

It is not the intention to create a reader of this post to a foundation airbrake expert; therefore, I will not get into detail as to how friction converts kinetic energy into the heat necessary in a foundation airbrake system to stop an 80,000# GVWR-CMV; therefore indicating friction fade issues as denoted above, as opposed to mechanical fade where the drum pulls away from the friction material due to expansion due to overheating; again, as described above in real world terms.  

The reason for the brief explanation as aforesaid is to demonstrate that there may be one or more brake fade issues in a crash. Each crash where brake issues are of concern should be thoroughly investigated in so that if the defense is harmless in the causation as to brake failure, elimination of brake fade and proper maintenance is critical.

Juxtaposed to the above; if a plaintiff is the victim of a crash, believed to be due to poor brake maintenance, and brake fade is a causation issue, a proper inspection of equipment and maintenance records is likewise critical.

Little did George Westinghouse, the inventor of the Foundation Airbrake System in 1872, ever expect to see his invention be used on millions of CMV’s throughout history. 

© Copyright 2012-2014
Scott L Turner
Slturnerconsulting.com