Worn and Forgotten

Most trouble free = most neglected in medium duty vehicles.

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.

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