Trailers: How to Ensure Safety for the Long Haul

Mon October 21, 2002 - Northeast Edition
Darryl Seland

As anyone who has ever taken a family vacation can attest, getting there is half the battle. The evolution of the trailer has made it easier for the construction industry to wage this battle, but according to many trailer manufacturers, it is still vitally important to follow maintenance schedules and develop sound safety practices to ensure trailers are operated safely, perhaps even more so than with other heavy equipment.

“If a trailer screws up, the family in the minivan traveling behind them dies,” said Flow Boy. “If a wheel loader burns up a bearing, only money is lost.”

Almost all manufacturers provide maintenance schedules with their operation manuals. Load King follows up its trailer sales with a Pre-Delivery Inspection (PDI) form, which contains a checklist for 2,000-mi. (3,218 km)/30 day maintenance, and requires its dealers to submit all signed PDIs it receives to help encourage buyers to follow the schedules and procedures.

“There is a wealth of information about [trailers] and usually it’s free,” said Don Knutson, sales manager of Towmaster.

Knutson pointed out that, “Highway laws apply, so not only does everything have to work properly, you must also be legal. Most states require trailers over 10,000 lbs. to be inspected yearly and certified.”

The Top Five

Due to heavy loads and difficult road conditions upon which trailers are operated, they are subject to considerable abuse. Continual maintenance is required because structural and parts failure of varying degrees may result at any time, according to Load King product literature.

In fact, moving parts, by nature, require a great deal of scrutiny to ensure safety. “The running gear [tires, axles, brakes] should be visually inspected daily as this encompasses your most common wear items,” said Knutson.

These wear items are predominant in manufacturers’ lists of the top five areas that require regular maintenance: tires, bearings and fasteners, electrical components, lug nuts and axles.


The No. 1 cause of tire failure is improper inflation. This can cause a trailer to “dog track or sway.” Because tires can lose a couple of pounds of air pressure a week, tire pressure should be checked frequently, while the tires are cold. Tire wear also should be checked to reveal any alignment problems.

Bearings and Fasteners

According to many manufacturer specifications, bearings should be tightened and repacked yearly, or every 12,000 mi. (19,312 km), whichever occurs first. Some manufacturers have attempted to make this repair less difficult.

“[Towmaster] offers E-Z lube hubs on trailers to make repacking the wheel bearings a quick and easy job done with your grease gun,” said Knutson.

While following the schedule is very important, following the specifications is equally important. According to Flow Boy, tightening all suspension fasteners to factory-dictated specifications after the first 1,000 mi. (1,609 km) is, “absolutely critical.”

The Electrical System

Wiring and lighting systems should be checked frequently because of their use in transporting over the road. “Lights that don’t work can get you a ticket or worse, into a traffic accident,” said Knutson. The manufacturer describes its lights as easy to change. “Simply unplug the wire from the old light and plug it into the new light, reinstall into the rubber grommet and it’s done,” said Knutson.

In addition, the company’s wiring harness features automatic reset circuit breaker on every circuit.

Another crucial part of a trailer’s electrical system is the breakaway battery. This battery is part of a system that stops the trailer if it breaks free from the towing vehicle. The breakaway battery needs to be recharged at least every 90 days and should be checked before every use.

Lug Nuts

Lug nuts should be checked and retorqued every time the wheel is removed for servicing. If the wheel has been run with loose lug nuts it will damage the holes where the studs come through, said Knutson. The only fix for this is a new wheel.

So, if the regular wear on moving parts require so much attention, how important is it to follow guidelines for load limits on a trailer? Very important. According to manufacturers, never overload a trailer. “Overloading bends axles, overstresses the frame and shortens the life of the trailers,” said Knutson.

The Result of Poor

Maintenance Practices

Knutson summed up the case for regular trailer maintenance. “When [a trailer] stops, you’re stranded,” he said. However, all the maintenance in the world cannot make up for diligent use of common sense.

A man working for a septic tank service died while attaching a trailer to a hookup on a dump truck. As the man leaned over to fasten the trailer, another drove a backhoe onto the back of the trailer, forcing the front of the trailer up. At the time the man’s head was between the tongue of the trailer and the bottom of the truck.

On Aug. 15, 1998, a 19-year-old construction worker was killed by a double tractor-trailer while excavating large amounts of dirt from a site on the UCLA campus. The worker fell under the bottom dump trailer while it was still moving after disembarking from a loader he was working at the site. The trailers were lined up to haul away the excavated dirt. Each trailer weighs between 30,000 and 35,000 lbs. (13,607 and 15,785 kg) without a load. Authorities still do not know why the worker left his cab.

In October 1999, a school bus was carrying 44 students, 5 to 9 years old, on a field trip in Schoharie County, NY. The bus was hit by a dump truck towing a utility trailer.

While no one was seriously hurt, an inspection of the trailer discovered the absence of a tractor protection system, a system required to protect the air supply of the towing vehicle in case of a catastrophic failure in the trailer brake system.

The vehicle was never properly tested to make sure that the protection system was working. Testing the protection system entails removing the emergency brake and disconnecting both air lines from the towing vehicle. When the air has stopped flowing, the brakes are applied, and the glad hands are checked for escaping air.

The investigation found that the truck exhausted air from the glad hands when the brake was applied. The NTSB has since recommended that all inspections include testing this mechanism.