Worn and Forgotten

"When thinking about vehicle maintenance, most people think about engine oil and filters, transmission fluids, axle/differential fluids, air filters, coolant levels, brakes, lights and tire pressures. Dealing with the steering and suspension systems, unless there is a problem, seems to go unnoticed," says David Peno, business unit manager in steering technology for ZF Sales and Service, North America, LLC.

Peno says that one of the most important steps maintenance managers can take is just getting the truck into the shop for a visual inspection as part of a scheduled maintenance program.

"One thing to remember is that no leaks in the steering system should exist. Any leak identified needs to be addressed immediately," he says.

From pumps to reservoirs, filters to gears, steering wheel to front axles, Peno says correctly identifying what component should be replaced is a hurdle for many fleets. All too often, the wrong components are exchanged, costing fleets more money in repair, when the solution could have been as simple as checking fluid levels or changing a filter element.

"The steering system is designed to be as maintenance free as possible. There are certain maintenance checks that are requested by the manufacturers that need to be adhered to."

Peno says that if the operator identifies a steering system-related problem, it is most important that the problem is clearly identified. For example, it should be determined when the problem happened, and how long has it been occurring.

"Starting with the simple basics such as proper oil level, type and condition should be utilized. If the oil is contaminated, just changing the fluid and filter does not necessarily resolve the issue. You need to find out why the fluid is contaminated, and if the steering lines, pump or gears are also contaminated. Proper diagnosing is key before taking any corrective action," he says.

Freightliner's take on steering components is a scaled down version of their class eight steering systems. Sean Tabari, project engineer in chassis engineering, says maintenance-free doesn't necessarily mean maintenance free.

"Drag links should be checked for tightness of the end sockets routinely. Plus, they have to be greased every 100,000 miles," he says.

Tabari also says the intermediate shaft (I-shaft) deserves some attention as well.

"The entire I-shaft in our design is also virtually maintenance-free. However, visually checking the I-shaft and the tightness of the U-joints routinely is ideal."

Bob Crepas, product specialist in commercial vehicle service for the Dana Corporation, says the best way to prevent steer axle component wear is to understand correct greasing procedures.

"There are three key areas every maintenance professional needs to know to properly grease: how often to grease; how to grease; and how to select the right grease."

"Knowing how often to grease depends upon the application in which the vehicle is operating," Crepas says. "For instance, a vehicle operating in the southwest, traveling for the most part on the highway, would not be exposed to large amounts of contamination and would not need to be greased as often as a vehicle operating with a majority of its time in an off-road application in Canada.

"It's important that the maintenance professional understands the environment in which the vehicle is running. They may need to grease at greater intervals than recommended, ensuring that the steer axle components do not wear out prematurely."

Second, knowing how to grease is equally important. Crepas says the key here is to always make certain that you apply enough grease to push out the old grease with its contaminants.

"Some people think you can add a small amount of grease and then stop. That's not the case. Keep greasing until you see fresh, clean grease coming from between the shim pack and/or the thrust bearing to beam interface. When greasing a tie rod end, apply the same method; grease until the contamination is pushed out."

Finally, once you've identified how often and how to grease, you still need to make sure you're using the right grease, Crepas says.

"Dana recommends the use of a heavy duty, multi-purpose, lithium base, #2 grade grease. Remember, never mix lithium-based greases with sodium-based greases."

Crepas says the biggest issue he sees is the controversy over putting weight on or off the knuckle joints when applying new grease during the colder, winter months in the North.

"Because grease tends to thicken in the winter, you occasionally have to jack up the truck to make sure you're getting the grease where it needs to go. You should see the grease coming out through the shim pack at the top, and at the thrust bearing at the bottom of the king pin joint. If you are not seeing this, you need to jack up the truck to take the load off of the front of the vehicle or off of its wheels," he says.

Winter not only wreaks havoc on grease, but also can distract from a proper visual inspection of the components during preventative maintenance (PM).

According to John Wappes, senior product engineer with suspension and steering for ZF, washing underneath the trucks is the first step to successful maintenance.

"Trucks being used in severe applications or the winter months with lots of salt and dirt should be power washed underneath the truck to help eliminate contamination, providing a clear opportunity to inspect the seals and other components on the suspension systems," he says.

He warns maintenance managers, "When you are washing, it is important to remember to have just plain water. Chemical degreasers can attack the seals and other components."

Wappes says the biggest thing fleets can do to get the longest life out of the suspension is to keep the joints and areas clean so technicians can observe the joints and all of the moving parts.

"Cleanliness is important because if you tear a rubber boot on a joint and don't see that, then you are going to allow water and foreign material into the joint and shorten the life of that component."

Wappes says one component failure will set off a chain reaction.

"If one part starts to wear faster than the others, it becomes the weakest link and will start to wear other components along side it as they compensate for its accelerated wear," he says.

Ingress and contamination are battles Wappes fights on suspensions.

"Anywhere from axle seals and bearing seals to the bearing seals for our linkage components—keeping contamination out is one of our chief design goals," he says.

"Anytime one of our seals is actually compromised or damaged by items in the environment, suddenly that contamination has free reign to enter the moving areas or any place where there is a need to keep it out and will increase wear exponentially."

Once contamination conquers a component, replacing the seal isn't the solution.

"It's a mistake to try to replace a seal," Wappes says. "If you are ever in the situation where the seal on a suspension component is damaged, that means the contamination has gotten into the joint, and if you just replace the seal, you are locking the contamination in. You actually need to replace that joint if the seal has been damaged to ensure the longest life out of all of your components in the system."

According to Ben Smith, front end suspension and steering manager for Freightliner, something maintenance managers need to keep in mind is that the materials the truck's suspension is made from will affect how maintenance should be performed.

"It is our recommendation to use maintenance-free rubber bushed front suspensions, but if the fleet uses the graphite bronze or non-rubber bushing type suspension, then it should grease the bushings approximately every 30,000 miles. If the grease is gone, parts don't move and then you have binding and you will run into issues," he says.

Dan Gadowski, chassis engineering manager for Freightliner, says the other thing that should be checked on a regular basis is the tightness of the suspension clamp group.

"The axles are bolted to the suspension with U-bolts," Gadowski adds. "It is important for maintenance managers to visually check the clamp group for signs of loosening. Also check the U-bolt torque per vehicle manufacturer's specification. If left unchecked it can lead to other failures and a costly repair bill."

Maintenance recommendations from the original equipment manufacturers (OEM) is the best way for maintenance managers to configure a maintenance schedule for their trucks.

"We use a combination of truck manufacturers' recommendations combined with the manufacturer's recommendations from the mounted equipment we use on our trucks," says Wesley Keller, transportation manager for PPL, an electric and gas utility in Pennsylvania.

"We bring the trucks in on a calendar basis, because some of the components or devices require an inspection every so many days. We tie basic inspections in with that," Keller says.

"Some may say we are crazy for bringing the trucks in every three months instead of by miles, but because of the aerial devices and because the truck is already in the shop, we just inspect everything routinely."

"PM is a way of life for us," Keller says. "We don't really have any issues we can't handle as far as the suspensions are concerned. The springs will arc with fatigue or occasionally break because we utilize the chassis at maximum capacity. We know we load our suspensions, but the breakage isn't premature. We expect that this will happen because of how we are loading them down."

ZF's Wappes wants to remind maintenance managers that some parts are made to wear.

"Tie rod ends, draglink ends and torque rods all have wear take-up built in. Once the wear has exceeded the take-up allowed, the part will develop lash. Lash indicates the end of the part's life, signaling time for replacement," he says.

"If you don't replace them before they wear too much, they could come apart and you could run into major problems," Wappes concludes. "Knowing and understanding this will help prevent major structural problems down the road. Not all parts are meant to last forever."