“As more aerodynamic improvements are added to trucks and trailers, they are creating a bigger ‘tunnel effect’ under the vehicle, significantly increasing the air temperature and thus the stress on components such as ujoints.” –Jim Holman, chief engineer-drivershaft products for Dana Holding Corp.
Ah, pity the poor universal joint assembly – more commonly known as a “ujoint” within the trucking community. Tucked away out of sight and often out of mind under the belly of today’s trucks, ujoints find themselves dealing with ever increasing stress due to higher under-vehicle air temperatures and greater torque loads.
So it’s no wonder component makers are working up new ujoint designs, to handle the harsher work environments these products now face. For whether you operate heavy- or light-duty trucks, the ujoints remains a critical linchpin between the engine, transmission, and axles – transferring ever-greater amounts of engine power to the wheels with no relaxation in standards for durability, reliability, and longevity.
[Here’s just one example of a ujoint in action; a light-duty model that’s developed a nasty knock due to the rigors of its job requirement.]
Now, though, Dana Holding Corp. is rolling out a new ujoint design for heavy-duty trucks – one designed to handle the increasing amounts of punishment increasingly being dealt out on a daily basis underneath the chassis.
The company’s new Spicer Life Series (SPL) Model 250 for Class 8 tractors is designed to offer a 40% improvement in dynamic bearing capacity to create a driveline with 70% more power density compared – all within the same-sized package as previous versions, according to Jim Holman, Dana’s chief engineer for driveshaft products.
Some of the new features of Dana’s SPL-250 ujoint include a new bearing package with larger needle bearings for increased capacity, a special Viton synthetic seal for improved grease retention and serviceability, and a thermoplastic seal guard to exclude contaminants. In addition, the company is “factory filling” the new SPL-250 with synthetic lubricant to help boost bearing life past its initial three-year/350,000-mile lubrication interval.
So, why all the hubbub in this space over this new component? Actually, it’s actually in response to how the environment under today’s Class 8 truck chassis is radically changing, requiring a shift in thinking about how fleets take care of components living “down under” so to speak.
“As more aerodynamic improvements are added to trucks and trailers, they are creating a bigger ‘tunnel effect’ under the vehicle, significantly increasing the air temperature and thus the stress on components such as ujoints,” Dana’s Holman told me. “That’s happening due in part to the higher amounts of heat being generated by low-emission engines.”
It’s a vexing issue, because in the past, the free flow of air underneath a truck helped cool down components to a degree, he explained.
Now, with aerodynamic changes “walling off” the undercarriage, the only air flowing underneath a vehicle is coming out of the engine compartment – air already fiery in nature due to exhaust gas reciriculation (EGR) and other emission-control systems, Holman said. As a result, it’s not uncommon for under-chassis temperatures to reach 200 degrees Fahrenheit, he told me.
That’s but one reason Dana did what he calls a “360 degree” evaluation of the SPL-250 – and one outcome of that effortwas the development of a new synthetic grease specifically designed to operate in those extremely hot under-carriage conditions now being found under trucks.
Then there’s increased engine power to handle, as well. “Even though customers are slowing down to improve fuel efficiency, thus lowering the number of driveshaft rotations, more torque is being transmitted through each rotation,” Holman noted. “That’s increasing the force being applied through the ujoint in addition to the hotter air temperatures it’s being exposed to.
[You can see clearly in this shot how hard as ujoint works – and this is on a light-duty truck!]
Tom DeHaven, Dana’s senior manager for driveshaft products, added that there are typically five ujoints on a Class 8 truck – three “main” driveline ujoints and two on the inner axle. The SPL 250 is a main driveline joint, whereas the company’s SPL 170 – which underwent design improvements not long ago – are inner axle models.
The key with both, however, is regular preventive maintenance (PM) – checking them every time a truck comes in for service. “You need to check for looseness at every PM; you want your drivers and technicians to look at them regularly, just to make sure everything is OK,” he said.
The thing is, with fleets looking to extend service intervals on everything from engine coolant and oil changes, those PM checks are getting fewer and farther in between – adding to the need for design improvements, DeHaven said.
“In Europe, for example, they’ve largely gone to a maintenance-free ujoint design,” he said. “The problem is, truck operating conditions in Europe are very different from ones in North America – they don’t experience the true long-haul stresses on trucks we see in the U.S. That’s why we still encourage fleets to make regular checks on ujoints part of their PM practices.”
