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Whole Lotta Shakin’ Goin’ On

By on May 1, 2019

Are You Feeling Not-So-Good Vibrations?

If you’re into rockin’ out to the round-the-clock sounds of the pop music on SiriusXM 60s on 6, you’re no doubt familiar with two blockbuster hits. The first, Whole Lotta Shakin’ Goin’ On, was recorded by Jerry Lee Lewis in 1964. It was originally recorded by Little Richard in 1957, and later recorded by Elvis Presley in 1971. The second is Good Vibrations recorded by the Beach Boys in 1966. You know the words to the chorus: “I’m pickin’ up good vibrations. She’s giving me excitations.” While these songs, like many other 60s hits can really get your motor runnin’, shaking and vibrating—when it comes to what you’re feeling inside the cab of your late-model truck—are anything but good.

Over the last two years, the number of Class 8 vibration complaints has noticeably increased across the industry. A cursory examination is all that’s needed to begin understanding the root causes. Many Greenhouse Gas 17 (GHG17) engines generate higher levels of torque at 1,050 RPM versus their predecessors at 1,250 RPM. This dynamic alone has moved chassis harmonics to lower RPM, introducing a whole new era of vibrations.

Technology & Techs

Truck manufacturers are working fervently to update their vibration analysis techniques, and the equipment needed by a technician to successfully identify the root causes of these problems. Determining the root causes of a truck shake has always been somewhat challenging, but seasoned technicians already knew that 85 percent or more of the vibrations felt by drivers originate at the wheel ends such as tires and/or brake drums. Although I’ve just started analyzing the scope of these perplexing new problems, I can already tell you that modern vibrations are becoming more common in driveline and front-end components like kingpins.

Some manufacturers are requesting that technicians add steering stabilizers to help reduce steering shake. Some maintenance experts are telling me that this does stop the shaking but only for a limited time. Eventually, kingpin bushings wear out from the frequency working through the frame, and the problem resurfaces. Replacing the kingpin bushings will fix the problem but it’s not cost effective to replace kingpin bushings prematurely or frequently.

Multiple Root Causes

Homer-2To compound these problems, engine manufacturers are using more asymmetrical fuel injection designs. This simply means that they’re shutting off fuel flow to half the injectors and adding fuel flow to the other half. This imbalance helps complicate the situation because it changes the engine harmonics, so a technician may need to hook up a computer to help diagnose a vibration felt by the driver. I know this sounds weird, but it’s the result of very smart engineers being creative to meet the EPA’s fuel efficiency and emission requirements.

Another area to keep an eye on is the suspension system. Some trucks now have electronically controlled air-ride systems. This is a wonderful thing if they’re working properly and if no one tampers with them. If an air-ride system makes an incorrect auto-adjustment or is manually adjusted incorrectly, poor driveline angles could result. According to TMC RP 611, the working angle of a driveline should be one to six degrees. Some truck manufacturers have very unique working angles, so their service literature must be carefully referenced. When the angles are out of spec, very bad vibrations move through the driveline and can destroy transmissions, engines, rear ends and other driveline components.

Finally, keep a close eye on any unusual vibrations and get them checked out as soon as possible. The tremendous torque generated at lower RPM by modern heavy-duty diesel engines can be very destructive to truck parts that historically had no problem managing the same torque at higher RPM. It will take some time for industry engineering and design teams to adjust to these new vibration frequencies, but I’m certain we’re collectively up to the task.

Until then, rock on to the shakin’ and vibratin’ on SiriusXM 6. As always, thanks for reading Maintenance Matters and let me know if you have any questions that you’d like me to address in the pages of RoadKing. 

About Warren Eulgen

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