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While driving habits may be to blame for some truck-related issues, clutch damper performance is not among them, according to a drivetrain expert at Eaton.
To put it another way, while automated manual transmissions may take the driver out of the equation when it comes to shifting points, their impact on extending the life of clutch damper over that of a driver-controlled manual is nil.
“There’s really not anything that the driver does wrong that would cause an early wear-out or failure of the clutch damper,” said Eaton applications engineer Mike Garrison. “From that standpoint, I don’t think there’s a big difference between the AMT and the manual.
“The only difference I would say is that a lot the AMTs are really going for fuel economy—not all of them, but they’re going for fuel economy or down-speeding and that just puts you in an operating range where the driver may notice some vibration a little more than he would otherwise because he’s operating at lower RPMs. But as far as the driver doing something to cause an issue I really don’t think so,” Garrison continued.
However, there is one driving habit that can lead to increased driveline vibration but it shouldn’t be confused with a failing clutch damper. Drivers that cruise at low RPMs amid high torque levels may experience increased vibration.
“When you’re doing a pull on a grade, right before you have a downshift, you’re down at this low RPM, your RPMs are kind of steady because you have a 100 percent torque coming of the engine going through the driveline and you may kind of operate at that kind of condition for a while on a long grade and that’s a key point in time where this vibration shows itself to the driver,” Garrison said.
While there are times when a worn clutch damper may be to blame for increased vibration proving that can be a challenge. Thankfully shops can turn to a drivetrain vibration analyzer, or DVA, to help pinpoint an annoying resonance.
“An experienced person can’t often tell if it is coming from a U-joint or something else within the system,” Garrison said.
If the clutch damper is to blame for the annoying resonance, it’s best to replace it with a clutch damper that falls within the original specs. Garrison said an over spec trend rears its head from time to time and it can lead to problems.
“Some people may think, ‘Well, a higher rating, or bigger might be better’ kind of thing. But we usually don’t recommend it because when you over spec the clutch from a torque standpoint you’re not getting as soft a rate as you could otherwise,” Garrison said.
“In other words, it’s probably a stiffer spring to handle some artificial torque level that’s not there so your springs are actually stiffer then they need to be and probably stiffer than the original clutch which can actually change some of the original characteristics and not in a good way,” Garrison continued.
Stiffer spring rates in a clutch damper mean more vibration which can affect driver comfort and lead to durability or wear issues on various components. Softer spring rates help to better absorb engine vibrations that travel down the driveline during the combustion process.
While space restrictions have minimized noteworthy design changes in clutch dampers, materials have evolved allowing for softer spring rates and improved damping performance.
