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Hydraulic Clutch Linkage: Keeping in touch with the clutch

Hydraulic clutch linkages are becoming more prevalent in the North American trucking industry. Here’s why your clutch selection is more important than ever when running trucks with hydraulic linkages.

In recent years, heavy-duty truck manufacturers have begun introducing vehicles with hydraulic clutch linkages. Manufacturers say they’re easier to package into today’s complex vehicle chassis and also easier to install during assembly.

Many drivers like them as well, because they require less pedal pressure to disengage the clutch. However, despite the advantages to manufacturers and operators, fleets and owner-operators need to ensure they specify self-adjusting clutches like Eaton’s Solo Advantage series, to ensure they don’t suffer some unintended consequences.

Because a hydraulic linkage places a pressurized fluid between the pedal and the clutch, the free play that a driver can normally feel in the clutch pedal is lost. This means drivers will not be able to identify the reduction in free pedal that normally warns them that a non-self-adjusting clutch requires servicing or an adjustment. Failure to recognize these traditional warning signs can lead to premature wear or failure of the clutch.


“With a mechanical linkage, the driver can feel the reduction in free pedal as the clutch wears,” explained Benjamin Karrer, product strategy manager for clutches with Eaton. “This reduction in free pedal provides an indicator to the driver to bring the truck in to have the clutch manually adjusted. With a hydraulic linkage system, because the free pedal is totally eliminated, he or she doesn’t have the same level of feel. So the driver has to be very, very good about bringing the truck in for service regularly and having that clutch wear checked to see if it needs to be adjusted, which often doesn’t happen.”

Losing touch with the clutch can have some undesired outcomes. A manual-adjust clutch that isn’t re-adjusted as required can suffer a shortened service life.

“As it goes out of adjustment, the clutch yoke can begin to make contact with the clutch cover and do serious damage to the clutch and the release mechanism,” Karrer warned. “Or, the clutch can begin slipping and that heat can damage the clutch so that a new clutch is needed. The flywheel could be damaged as well if it gets too hot.”

Typically, a manual-adjust clutch will need to be re-adjusted a minimum of 13 times through its life-cycle. If just one adjustment is missed, the clutch may have to be taken out of service well before its intended lifespan.

This is why Eaton strongly suggests using self-adjusting clutches such as the Solo Advantage series on trucks with hydraulic and mechanical linkages. The truck OEMs, in most cases, now offer Solo Advantage clutches as standard equipment. However, it’s equally important that the appropriate, self-adjusting clutch is chosen for replacement in the aftermarket, Karrer stressed.

“We really view the Solo Advantage self-adjust clutch as the only reasonable option for someone to install in a truck with hydraulic linkage,” Karrer said. “I think a great deal of education is still required. We’ve been working to promote that message. In the aftermarket, I think we still have a lot of opportunity to improve our messaging about what clutches work best with hydraulic linkages.”

There are benefits to using a self-adjusting clutch, not the least of which are the reduced maintenance requirements and their associated costs. A clutch adjustment can take anywhere from 15 to 30 minutes to perform. Extrapolated over the 13 re-adjustments a manual-adjust clutch will typically require, the maintenance savings alone can be significant.

And that’s assuming an operator is taking the vehicle in for a clutch adjustment whenever it’s needed - something that’s trickier to do when a hydraulic linkage is paired with a manual-adjust clutch.

“If someone is very good about doing their adjustments on their clutch, the savings is really the labor of doing those adjustments,” Karrer explained. “But in many cases the adjustments don’t get done, and that’s an increased risk with hydraulic linkages and that’s why the Solo Advantage has so many benefits. The real success here is making sure the clutch isn’t damaged before everything is actually worn out, and that’s what the Solo Advantage helps you do.”

As far as maintenance is concerned, Solo Advantage clutches, like Eaton’s Easy Pedal manual-adjust counterpart, still require greasing of the bearing and sleeves.

Is there ever a situation or application in which the Solo Advantage series isn’t a better option for fleets?

“Solo Advantage is designed to work in all applications, but for extreme severe-service applications, we encourage people to consult their local Eaton Roadranger representative,” Karrer advised. “They can provide guidance on the best driveline solution.”