Section III Corrective Actions

Following these six recommendations below will either greatly reduce or eliminate potentially destructive torsional resonances:

1. Specify Soft Damped Clutches for Manual Transmissions  All major clutch manufacturers offer certain design features in some model 14-inch and larger clutches that significantly reduce the risk of destructive and discomforting drive train vibrations.

   One of these features is stiffness (or compliance). These clutches offer torsional spring rates that are less than half of the rates of other clutch models. This helps to lower the engine speeds at which torsional resonances occur, and minimizes the risk of incurring engine firing excited torsional within the operating range. Another feature is damping. Controlled hysteresis or friction damping reduces the amplitudes of torsional resonances excited in the speed range by engine pulsation (firing or half firing frequency) driveline-induced acceleration. Specifying this type of clutch at purchase will substantially reduce all of the risks outlined in Section I, except for extreme driveline angularity problems.

2. Ensure Proper Driveline Angularity -  If a soft damped clutch is used in the drive train, the guidelines and diagrams shown in RP 610A are appropriate. Generally speaking, for a two-joint driveshaft at 2500 RPM or less, a maximum working angle of six degrees with cancellation of not more than two degrees will meet this criterion. If the joint working angles are not cancelled properly, component corrective action will be necessary. Some axles offer top mounted carriers/differentials that enhance driveline geometry particularly, in short wheelbase vehicles. For automatic transmission driveline design requirements access your automatic transmission supplier's website. Most transmission and axle suppliers have websites for driveline angularity. See manufacturer's website, or contact your OEM representative for example.
3. Do Not Vary Air Ride Suspension Ride Height From Factory Specifications -  Because the driveline angularity is so sensitive to ride height, no adjustments should be made to ride height factory specification. Fleet managers and vehicle operators should be made aware of the factory specification. Maintaining proper ride height is required and should be listed as a maintenance item. If proper ride height is not within factory specifications failures may occur.
4. Consider Drive train Components With Internal Damping Features When Purchasing New Vehicles Or Replacement Components -  Some transmissions and axles currently offer or may develop internal damping. These components will effectively reduce resonant amplification of engine or driveline pulsations and their ill effects.
5. <Avoid Sustained Operation at Extremely Low Engine Speeds -  Even in vehicles with soft damped clutches, sustained engine operation, particularly at wide open throttle, should be avoided below 1200 RPM. Operation at extremely low speeds presents high risk to component life.
6. Consider Installing Viscous Driveline Dampers on Units Already In-Service -  These bolt-in devices may be a cost effective way of dealing with noise, vibration, and durability issues resulting from torsional resonances being excited, particularly for vehicles already in service. Manufacturers of these devices should be consulted along with the manufacturers of the components to which they attach - prior to their use. Some automatic transmissions have clutch dampers that isolate the transmission and the rest of the drive train from most of the engine excited torsional vibration. Contact your automatic transmission supplier for more details.
7. If purchasing tandem axle configurations consider the addition of a lubrication pump.  By providing added lubrication to the moving components in the Inter - axle differential area, damage due to torsional vibrations can be minimized.
8. Routine maintenance is required of all drive system components  such as universal joints; slip yokes, carrier bearings etc.