GotQuestions? Transmissions

Q. What are torsional vibrations?

February 26, 2016

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A. Torsional vibrations occur because of the firing of the engine cylinders and the sudden high pressure forcing the piston down. All engines produce torsional vibrations, and all drivelines have natural frequencies at which they will vibrate. The problem occurs when the vibration the engine produces at the normal cruise RPM consists of the same frequency as the driveline’s natural vibration frequency so the driveline will develop vibration at normal cruise. The clutch damper is the key vibration tuning element for the whole drivetrain. It shifts the natural frequency of the drivetrain to below that produced by the engine.

Comments

  1. 1. Steve Nauer [ March 08, 2016 @ 06:29AM ]

    I have a 2015 Silverado that appears to be doing this, and it is most obvious when traveling between 50-55mph in the four cylinder mode. Is there anything that can be done to resolve this? Could this affect the life of the engine? Could this affect gas mileage as I am getting worse mileage than friends that have the same vehicle. Thanks.

  2. 2. Jim Allen [ June 09, 2016 @ 02:48PM ]

    Hi,
    Have you ruled out tire/wheel/bearing vibrations at the wheel ends ? A bad U-joint, or possible premature bearing failure in a drive train component ?
    Next, have you checked for GM service bulletins, and online, or a mechanic familiar with the vehicle, you trust ?
    The engines balancer, (vibration dampened, can fail. Viscous dampeners are vulnerable to sharp blows, and old age
    The silicone fluid, can harden prematurely. The conventional type balancer can have the outer ring slip, creating an out of balance condition.
    Transmission torque converters, and starter flex plates, can have the fasteners stretch, loosen, etc., and cause vibration.
    The fuel mileage issue may simply be differences in driving practices, (style) or a missing faring. Lift kilt, tire size, and camper shells affect mileage, not always favorably.
    Aftermarket parts can also effect mileage, and performance. Air intake, exhaust, "chips", manifolds, headers, throttle bodies, and internal part changes, (camshaft, rocker arm, etc. modifications, bigger injectors, can also change mileage. Up, or down. The single biggest cause of variations in mileage is the driver. Then GVW, and geography. Heavy loads in mountain terrain vs light to no load, and flat terrain. Vehicle speed contributes, the higher the speed, the higher the fuel consumption. This is where lift kits, tire size matter. Lifting a vehicle exposes the undercarriage to air flow, drag follows. Turbulence is created by the air disrupted by the now exposed drive train. Big fat tires also push a lot of air. Wind resistance is increased by the exposure, to added drag, and the higher the speed, the higher the resistance. The higher the resistance the higher the demand for power to overcome the resistance at the speed traveled.
    Worn injectors affect mileage, add to the torsional vibration, by the excess, and uneven flow each time they hit. This can change the frequency of the vibration, as does, bent driveshafts, worn slip joints, and U-joints.
    I suggest checking GM service bulletins, and as many sources as you can to learn if these particular vehicles, components, and/or combinations of these. It's the simplest thing to check, and you won't get your hands dirty.

 

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Brian Fletcher

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Brian Fletcher is one of over 200 Eaton Roadranger® representatives out in the field making more than 27,000 combined face-to-face visits a year. Like every Roadranger representative, he’s dedicated to providing industry-leading Solutions, Support and Expertise to fleets across North America.

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