Equipment Maintenance: Articulated Trucks
| June 12, 2007 |
Articulated trucks have been around since the mid-60’s but in the last few years have become much more popular. With their 360-degree rotation hitches and four-by-four and six-by-six drivelines, artics have always been technically advanced machines. Yet the newer models are becoming even more sophisticated – primarily in the transmissions, engines, brakes and hitch designs. In most cases the increasing sophistication means the machines will cost more upfront and cost less to maintain over their useful economic lives. But contractors, manufacturers and dealers are just now beginning to get a handle on the lifecycle issues involving the current generation of trucks.
Not like other trucks
“The articulated truck is built for speed and flotation,” says Jerry Witt, equipment sales manager for Ziegler, a Caterpillar dealer in Des Moines, Iowa. “It’s not built like an off-highway truck, with big huge castings in its frame that have 35,000- and 40,000-hour design lives. Scrapers and rigid-frame trucks are more tolerant of abuse, but if you choose to operate your articulated truck this way, you’re going to suffer.”
A rigid-frame truck typically runs on well-maintained roads with 8 to 12 percent rolling resistance, so the driveline load is consistent throughout its life. But for an articulated hauler, the operating conditions change from day to day and minute by minute.
“Articulated haulers can have rolling resistance demand up to and over 40 percent,” says Buddy Goodman, product marketing, articulated haulers for Volvo Construction Equipment. “The higher total rolling resistance results in more load on the driveline and that’s going to affect the component life.”
Predicting an average lifespan
As with any earthmoving equipment, the useful economic life of an articulated truck can vary widely. A number of operating conditions can have a negative impact, says Bryan Flanigan, director of hauler marketing and sales, Terex. These include soil abrasiveness or coefficient of traction, excessive use of differential and axle locks, road and site conditions and lax maintenance procedures.
Rented artics average about 1,500 hours of use per year, Flanigan says. Contractor usage runs more in line with 2,500 hours per year. Depreciation can be scheduled over five years or 10,000 hours, but the useful machine life will run about 10 years or up to 20,000 hours, Flanigan says.
Care and repair of engines
Engine life often serves as the baseline for equipment life, since that is typically the most expensive item to rebuild or replace. “If somebody isn’t taking care of them, if they are abusing them, if they’re running them rough and throwing a different operator on them every day, then in 8,000 hours they’re probably going to be replacing engines,” Goodman says. “On the other hand, I’ve seen 35-ton haulers well cared for with engines going out as far as 22,000 hours.”
Jeff Feeley, Zeigler’s service manager, says a typical engine lifecycle history on Caterpillar artics he services would include several intermediate steps before complete replacement. These might include a turbo cartridge at 5,000 to 6,000 hours, a bottom end rebuild with rod bearings and main bearings at 7,000 to 8,000 hours and an in-frame rebuild with a set of rings, new rod and main bearings, liner packs and reconditioned cylinder heads at 12,000 to 13,000 hours.”
Costs for the turbo kit run about $900. Replacing the rod and main bearings costs $2,500 to $5,000. An in-frame overhaul prices out between $9,000 and $11,000, but this maintenance should take the engine close to 20,000 hours, Feeley says. A complete engine replacement runs $12,000 to $18,000 depending on the make and model.
Manufacturers are putting a lot of effort into building transmissions specifically for the unique demands of articulated trucks.
“The advancement of transmission technology has given these components a much longer life cycle,” says Martin Meissner, marketing services manager for ZF, which supplies transmissions for Case, Terex, Link-Belt, Moxy and Astra articulated trucks. “Decisions that were made by the operator in the past, such as retarder activation, shifting patterns and differential lock activation, are being automated to ensure optimal performance and fuel economy and less wear and tear on the driveline.”
The newer transmissions have only been in service within the last two years, not enough time to evaluate their impact on lifecycle costs. The older transmissions will run from 8,000 hours in tough conditions to around 10,000 hours in normal operating conditions, Flanigan says. You can expect similar longevity out of most of the other driveline components, including the torque converter, differentials, drop box and final drives.
A partial rebuild can stretch out the life of your transmission by 20 or 30 percent and would cost anywhere from $6,000 to $15,000, depending on its condition. But partial transmission rebuilds are not always warranted. Witt says if you go this route, you should have a good history of oil samples to verify the condition of the components within the transmission. Complete replacement of a transmission may cost up to $20,000.
Dick Carrington, product support manager for Hayden-Murphy Equipment, a Terex dealer in Bloomington, Minnesota, emphasizes the need to also replace the transmission oil cooler after a transmission breakdown. “Some people try to clean them and they think they’re flushing them well enough, but they’re not,” he says.
The articulation hitch
“We’ve gotten a lot smarter on the hitch area,” Witt says. “We’ve found that if you put an automatic lube on that area you eliminate 95 percent of the problems. But it took us a while to figure that out.” Knowing this, Ziegler is considering putting auto lube systems on all its rented artics, Witt says.
Volvo’s D series artics have gone to a maintenance-free design, but before that the C series had four grease points. “I found that the guys who were greasing the hitch daily could go four times longer before they had to make adjustments,” says Richard Iddins, product marketing, articulated haulers for Volvo Construction Equipment. “Guys who were only greasing at 250 hours were having to make the adjustments every time and replacing bearings well before 10,000 hours.”
Properly greased and adjusted, the articulating hitch should hold up beyond the average engine life. Rebuilding one costs from $6,000 to $8,000.
Tires have a big impact
“Correct air pressure is critical to the performance of the tires,” says George Harris, senior OTR engineer for Continental General Tires. “When the pressure is too low it will destroy sidewalls or cause separations; too high and it causes failure due to cuts.” Under-inflation also increases the rolling resistance of the tire and therefore increases the fuel consumption. At a minimum, Harris recommends weekly air pressure checks.
Daily visual inspections are important. “Anytime you have cuts that expose steel cords you need to get that repaired or replaced,” Harris says. Letting a damaged tire run to failure is not only unsafe, but guarantees that at some point you are going to incur expensive downtime.
Mismatched tires on opposite ends of the same axle can cause problems too. Tires with different rolling resistance will put unequal strains on your differential and may cause it to wear out prematurely, Harris says.
Tire longevity depends on soil conditions. In abrasive sand, rock or gravel you may only get 2,500 hours on your tires, says Flanigan. In clay and dirt that may extend up to 7,000 hours.
Putting on the brakes
Manufacturers provide engine and transmission brake retarders and more recently sealed and oil-cooled brakes to increase the life and durability of this critical component.
“I’ve seen rigid-frame trucks with enclosed brakes go as far as 18,000 hours before the brakes need rebuilding,” Witt says. The newer sealed brake systems have only been available on articulated trucks in the past few years, but Witt says they should last at least 10,000 to 12,000 hours.
The older drum-style brakes are usually rebuilt around the 4,000-hour mark, Feeley says. On well-maintained brakes, replacing the wear parts costs about $1,500 to $2,000 for all six wheels. Replacing drum brakes that were damaged or destroyed due to poor maintenance, however, could cost upwards of $3,000 per wheel or $6,000 per axle, Carrington says.
Electronic engine and transmission controls have made it less likely that an unskilled operator is going to use excessive fuel, fail to engage the brake retarder or grind the gears down, but there are a couple of things less skilled operators do that can add significantly to the cost of maintaining an articulated truck.
“The worst opponent the suspension has is an uneven loading site,” Iddins says. “If a guy backs up a berm, lifts the rear axle loads in that situation, it’s very adverse to the suspension on the truck. That doesn’t mean he can’t sit on a slope, but the idea is to have all four wheels planted on the ground.” Iddins says spillage at the load site can also contribute to this problem.
Another problem that occurs with some frequency is rollovers, typically when an operator takes a curve too fast under load, or tries to drive with the dump bed still in the air. In addition to body damage, rollovers can damage the tilt cylinders – a $3,000 repair bill per cylinder.
Ejector trucks don’t have tilting beds and are less prone to tip-overs. Plus the center- mounted ejector cylinder is better protected against damage than side-mounted lift cylinders. Replacing a multi- stage ejector cylinder may run as high as $10,000, but can be weighed against the ability of this style of truck to reduce carryback and increase productivity.
On the positive side, the high level of automation in today’s articulated trucks makes it easier for contractors to put a new, less skilled operator in the driver’s seat. “Somebody who knows how to drive can get in these trucks and make them work,” Witt says. “They’re really pretty simple.”
Treat it right, it treats you right
Regardless of the technology, the key to keeping your lifecycle operating costs to a minimum on articulated trucks is maintenance – and more maintenance than you may be used to for other pieces of equipment, Carrington says.
Carrington says the proof is with the customers of the trucks he sells. “I have a customer in Kansas City with eight trucks and I never hear from the guy. And there’s another guy with three trucks and we hear from him every day,” he says. “It’s all in the maintenance. The customer in Kansas City has a maintenance program that’s far beyond anybody’s. That’s why we never hear from him.”