Too good to fail?
The technological improvements to fifth wheels have led to a false sense of security, and a recent rash of truck-trailer separations.

By Paul Abelson, senior technical editor

Why are we hearing so much about fifth wheel separations lately? For years – make that generations – fifth wheels have been among the most reliable, dependable and virtually indestructible components on trucks.

Back in the 1980s, a famous picture appeared in many trucking magazines. It showed a tractor that had crashed through a bridge guard rail and was hanging in mid-air, suspended only by its fifth wheel and the trailer’s kingpin. Today, with the Internet, the picture would have “gone viral.”

Since then, metallurgy and manufacturing practices have improved. Counterfeit fasteners that plagued transportation in the ’80s and ’90s have all but disappeared.

So what has caused these recent separations?

Fifth wheels have become so good they have become the most neglected equipment on trucks. But a confluence of forces, taken together, seems to be creating new problems. They involve the desire for better fuel economy, environmental considerations, improved engine design and manufacture and, most recently, severe weather.

Connecting to the trailer has become a process done by memory, not by checklist. Unless you drive for a slip-seat fleet that might have all three manufacturers’ fifth wheels, not to mention a variety of models, you should be completely familiar with your equipment and the way it feels.

That’s when the other forces start to come into play. Hooking up has become more difficult.

On the rare occasions that fifth wheels do not properly lock around kingpins, the mechanical reasons may involve poor lubrication or damaged components. Often, these can be detected before the trip begins. That involves a visual inspection. But it is becoming increasingly difficult to perform one.

Fewer and fewer drivers do visual inspection under their trucks. The vast majority rely on the “tug test.” But a kingpin can ride over the fifth wheel top plate and drop in front of it. The trailer’s upper coupler plate can then rest on the top plate, obstructing the view from the rear. During the tug test, the trailer will offer resistance and the driver will think the combination is connected securely. In most cases, this error is discovered as soon as the driver attempts to turn, often with damage to other tractor components.

The proper procedures for fifth wheel coupling and uncoupling are well known, spelled out, and illustrated in the Technology and Maintenance Council’s Recommended Practice RP653. Each manufacturer has training materials and videos on its Internet pages. The process starts before the fifth wheel makes contact with the trailer. Once the fifth wheel is under the trailer, opportunities for error increase.

Aerodynamic skirts are a major problem. They obstruct vision and access, often making it impossible to perform required visual and manual checks, especially in the harsh winter conditions recently experienced.

Extreme cold affects the ability of the grease to lubricate locking mechanisms. Lubes harden when cold, making opening and closing difficult. Partially closed jaws won’t lock. A rig that passed the tug test may be miles down the road when the jaws work open.

Too much grease on the top plate can be squeezed out to drop on the ground, becoming an environmental hazard. Some extra grease is necessary so that some falls onto the locking/opening mechanism to lubricate it. Too much grease also holds grime and grit. Instead of lubricating, it can actually abrade upper couplers, top plates and actuating mechanisms. During snow removal operations, grease may pick up corrosive chemicals. Just because a fifth wheel is greased, it isn’t immune from corrosion.

Too little grease is just as bad. Without enough grease, only a small amount gets to the locking mechanism, which will stiffen and bind. Check your owner’s manual for proper greasing instruction or check the videos each maker has on its Internet site. Inadequate grease can result in stiff steering and loss of control.

Some drivers use packets of fifth wheel grease available through truckstops and parts shops. When used according to directions, they work well. Clean the top plate before using the packets. Always scrape off all old grease before applying new. It’s a good idea to stay with one type of grease. Some synthetics are incompatible with petroleum greases and can cause a hard-to-remove gummy residue.

To avoid lube problems, manufacturers offer top plates with high-density polyethylene (HDPE) inserts. An HDPE upper coupler assembly, the Revolver, is available in the aftermarket. Lube-free fifth wheels still need mechanisms greased or oiled according to maker’s instructions.

Every fifth wheel has position indicators, visual signals that the locking mechanism is, in fact, locked. Most are tactile, so even if your view is obstructed by fairings, you can reach in and feel if a handle is flush in its locked position. Manufacturers also have locking indicators that light up or send a signal to an indicator on the dashboard that the fifth wheel is open or closed.

Because of the access problems, air-actuated fifth wheels are gaining popularity with fleets for safety reasons and among drivers because they don’t get dirty and greasy. These usually have remote locking indicators.

When trucks required preventive maintenance at 12,000 miles, fifth wheels were serviced frequently. Problems were almost unheard of. Today, with engine service at 25,000 to 30,000 miles, fifth wheels should be checked more often.

Start by steam cleaning or pressure washing; then inspect and lubricate moving parts. Always check for your maker’s specific procedures. Look for bent parts, weak or broken springs and signs of corrosion. If you have your own trailer, check the kingpin for wear and alignment. All fifth wheel makers have kingpin gauges.

With basic, regular maintenance and inspection, a fifth wheel can last the life of the tractor. But considering the job it has to do, it deserves and demands its regular service. LL