Heavy-duty: ZF presents new eMobility solutions for commercial vehicles
e until new fresh grease is being purged, indicating a complete change of grease has occurred.
While servicing the the U-joints, use the old grease as a diagnostic tool. “You should pay attention to what’s purging out of the cups,” says Salazar. “If there’s any signs of moisture in there, or the grease is black with a burnt odor or if there is a gray metallic look, those are all signs that something has gone wrong and there is accelerated wear in the U-joint. If you see water, that means the seal is failing and not keeping the contaminants out, so you need to replace the U-joint.”
In addition, it’s important that technicians purge all four cups, says Salazar. “You need to see fresh grease out of all four cups to ensure that you have fresh grease in all of them.”
It’s just as important to pay attention to what goes back in, say our experts. “Historically, we’ve allowed a fairly broad specification of EP2 high temperature grease, says Dana’s Holman. “Now we know a lot more about grease and its impact on U-joint life. With longer lube intervals, grease selection becomes more critical than ever. When you were servicing the truck every 10,000-15,000 miles, your grease didn’t have to be quite as up to the task as it is today when you’re only bringing it in every 100,000 miles. In addition, the emissions equipment now being put between the frame rails is raising the ambient temperatures around the U-joints quite a bit, so there’s more opportunity today for the grease to break.”
A standard universal joint, when lubed regularly at the specified intervals, will provide good life, explains Meritor’s Mayer. Some of the new upgrades are driveline-specific. Choosing a premium brand of universal joint is important to ensure that the design characteristics provide optimal sealing and lubricant distribution.
“The marketplace today has a product for every need. Some fleets or owner-operators prefer to grease U-joints while others choose the economic advantages offered by an extended lubrication interval design or a permanently lubricated design. Buyers (fleets) specify depending on their vocation/application and maintenance practices,” he says.
• Greasable options typically have recommended grease intervals for on-highway applications of 40,000-50,000 miles or corresponding to normal maintenance schedules.
• Extended lubrication options satisfy those who prefer to grease, while providing an economic benefit by reducing the number of required lubrications over the life of the truck.
• Permanently lubricated is the “best” of the good, better, best options. With this design, the manufacturer has assumed the responsibility for adequately lubricating and sealing the U-joint for the life of the truck. The U-joints do not have grease fittings.
Besides the obvious benefit of never having to grease the U-joints, there are several other advantages to permanently lubricated U-joints:
• Eliminate the chance of introducing unacceptable grease;
• Prevent the introduction of debris from a dirty grease tip;
• No danger from mistakenly skipping a scheduled lubrication interval.
Meritor’s Mayer is quick to point out, however, that regardless of manufacturer, a permanently lubricated product does not mean it is a “no-maintenance” product.
“The upgrades available today are focused on maintaining lubricants longer,” he explains. “Industry- or supplier-recommended inspections must take place at the appropriate intervals.”
Agreed, says Dana’s Salazar: “You shouldn’t consider any product ‘inspection-free.’ There are ‘maintenance-free’ products, and our driveline components are available with that option, but that shouldn’t keep you from inspecting them on a periodic basis. And not to belabor the point, but as engine torques continue to increase, it will put more strain on the U-joint. That means a high-quality U-joint from a reputable manufacturer is going to be more critical than ever.”
If a part needs to be replaced, is the best option an upgraded component? Not necessarily. Although the extended lubrication or permanently lubed U-joints are typically made to the same dimensions as other greasable designs, it’s strictly a matter of choice. Certain manufacturer designs may require a change to the corresponding driveshafts and yokes. While permanently lubricated U-joints are increasing in popularity, the older styles are unlikely to disappear entirely, experts say.
“Some fleets like the ability to service the U-joints when their vehicles come in for service,” explains Salazar. “One group of customers will want to continue to look at the driveline, inspect it and make sure they’ve lubed it. Another group of customers won’t want to touch it unless they absolutely have to and they’re already under the truck. The way we position our products is having the capability to service both types of customers.”
SKF’s Kern says that the best defense against sidelined vehicles due to U-joint failure is to inspect the U-joint and driveshaft regularly and lubricate on a specified schedule. Address the issue when the costs are minimal.
Dana’s Holman says this point can’t be stressed enough. “We do everything we can to communicate it through field bulletins, through our road ranger group, through fleet visits…As we talk to the fleet maintenance teams, we see a varied awareness of these recommendations.