Rigid frame trucks

|  June 12, 2007 |

If you have a 7- to 10-year-old rigid frame truck, chances are you could get a lot better lifecycle costs out of a new machine. During the past decade, rigid frame truck manufacturers have focused on lengthening component lifetimes and service intervals.

“All of the systems have been improved to give greater life,” says Francis Bartley, engineering manager, research and development, for Liebherr. “Engines and hydraulic systems have been improved and require less maintenance and have longer life. Most truck components have improved, creating lower maintenance requirements.”

Newer models also sport several technological advances such as electronic engines and transmissions, more efficient horsepower and onboard monitoring systems that lengthen lifecycles, increase productivity and make diagnosing problems and scheduling maintenance easier.

Long design life can include many rebuilds
The average hourly use on a rigid frame truck varies depending on its application. When working in mining operations where they are typically running 24/7, rigid frame haulers can log between 5,500 and 7,500 hours a year. Trucks operating in quarries usually accumulate 2,500 to 4,000 hours annually and rental rigid frames average 2,000 hours a year. The typical contractor user of rigid frame trucks puts 2,000 to 3,000 hours on his machines annually, working on projects such as constructing highways and moving dirt for site development.

Compared to other types of construction equipment, rigid frame trucks have a relatively long design life that can include several rebuilds. Forty- to 45-ton trucks have a design life of 40,000 hours, 60- to 70-ton rigid frames have a design life of approximately 50,000 hours and 100-ton haulers can last 60,000 hours, says Bryan Flanigan, product marketing manager for Terex. Rigid frame trucks with capacities of 200 tons or more have design lives of 60,000 to 80,000 hours, Bartley says.

You should consider several factors when deciding to keep, trade in or sell your machine. The condition of the truck is a primary factor, says Eric Berkhimer, manager of mining applications for Hitachi Mining Division. “Is the owner still getting good availability and reasonable operating costs?” he asks.

Over a truck’s lifetime, operating costs generally rise as it requires more and more repairs, Bartley says.

You should also look at the truck’s trade-in or re-sale value and at technology changes since the unit was purchased. New models may be leaps ahead technologically, offering more productivity, Berkhimer says.

Another factor to consider is the availability of a replacement machine, says Ron Cosper, customer service manager for Holt Cat in San Antonio, Texas. The larger machines may have to be ordered before they are built, so getting a new rigid frame truck may take four or five months, he says.

Haul faster, more efficiently with new technology
During the past three years, manufacturers have begun electronically programming engines and transmissions to work together. When the transmission shifts, it signals the engine to cut off power for a millisecond. This produces a smoother shift, better fuel consumption and reduces peak torque points that cause wear.

“Instead of operating independent of the transmission and the rest of the powertrain, you could connect the engine and the transmission and drive system together so it all operates as one unit,” Flanigan says. “They talk to each other.”

Bartley says the switch from D/C drive systems to A/C equipment has also made a difference in lifecycle costs. A/C equipment is more rugged and has a longer life. “The whole system requires less maintenance,” he says. “It has a lot more electronics and a lot less components to make trouble.”

Speeds on grade have also increased over the past seven to 10 years. Ten years ago, you could travel only 6 or 7 mph up a 10-percent grade, Flanigan says. Today’s trucks, on the other hand, can go 10 or 12 mph on the same grade. Because torque is multiplied not only in the transmission, but in the rear axle as well, you can now use the same amount of horsepower to do more work. A safe speed going downhill in a truck manufactured 10 years ago would also be 6 or 7 mph. But better cooling systems allow new trucks to travel down grades at 20 to 25 mph.

“People don’t just look at a rigid hauler as an engine, tires and a bed,” Flanigan says. “Speed is as important as payload. If a truck can maintain 12 mph on grade with 70 tons on it, you certainly wouldn’t want to put 75 tons on it knowing the speed is going to fall to 7 mph.”

Onboard weighing systems, developed in the past five years, can help you make sure your trucks are not overloaded. In some systems, a red light on the outside of the truck flashes on, letting the loading operator know the truck is loaded to the capacity the owner has set. In addition to monitoring payload, the weighing system can also keep track of cycle time, haul time and return time over a period of a week or longer. Machine systems can be monitored electronically on newer trucks, improving maintenance scheduling and leading to repairs before catastrophic failures.

Suspension systems have changed as well. Rubber pads, which allowed 2 to 3 inches of movement, were typically used in rigid frame truck suspensions until about 10 years ago, when manufacturers began using compressible fluids that allow 11 to 13 inches of movement. The technology, however, wasn’t universally used until about 1998, Flanigan says.

Advances in material and welding technology in the past 10 years have produced lighter trucks, creating opportunities for additional payload. A lighter machine also leads to longer tire life, lower fuel consumption and longer component life.

When to rebuild?
The first expected overhaul for most rigid frame trucks is in the 10,000- to 12,000-hour range. For larger trucks with capacities of 200 tons or more, the first major overhaul doesn’t occur until 15,000 to 20,000 hours, Bartley says.

The 10,000- to 12,000-hour overhaul usually includes a minor rebuild of the engine and transmission, Flanigan says. Most contractors Terex works with plan to sell their major pieces of equipment, including rigid frame trucks, as good used machines before the first rebuild. Contractors are more project focused, so keeping or selling a rigid frame truck usually depends on their work schedule. “I think it depends on the length of the job and how much other work they have for the machine,” Flanigan says. “They’re not carrying a lot of assets they’re not using.”

Holt Cat often rebuilds rigid frame trucks at the end of the machines’ first lifecycle. The dealership typically rebuilds trucks for customers, but sometimes purchases a truck, rebuilds it and sells it to another end user. Cosper says the price of a certified rebuilt rigid frame truck is usually 50 to 65 percent the cost of a new machine. This includes an overhaul of the engine, transmission, drive train and hydraulics.

Truck maintenance, haul road design affect operating costs
If you maintain your rigid frame truck according to the manufacturer’s suggestions, you will greatly reduce your operating costs. Change filters on schedule and repair hydraulic system leaks quickly. Repairing bearings or cracked or damaged components when you first notice the problem is important, Bartley says. You should inspect the machine for this type of damage every 500 hours.

You should also inspect your truck’s tires daily – or weekly at a minimum. “Look for any kind of noticeable cuts or snags that could take a tire out of service,” says Chris Rogers, marketing manager for Bridgestone/Firestone Off Road. You should check the tires’ air pressures at the same time.

How you maintain the haul road your trucks use will also affect lifecycle costs. Roads need to be smooth and well graded with properly banked turns. Typically, the more turns you have, the higher your operating costs will be because operators have to slow down.

And if you want to optimize production, fuel consumption, tire life and component life, the best grade is between 8 and 12 percent total grade, Flanigan says.

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