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      10-12-2019, 07:14 AM   #51
M Fifty
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Drives: M2 & 330CI
Join Date: May 2018
Location: The Interweb

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GM have a Patent on how to:

"Problematically, axle shafts frequently exhibit “powerhop” when a large amount of torque is applied thereto. Powerhop typically occurs when tire friction with respect to a road surface is periodically exceeded by low frequency (i.e., below about 20 Hz) oscillations in torsional windup of the axle shafts. Powerhop produces oscillatory feedback to suspension and driveline components and can be felt by the vehicle occupants, who may describe the sensation as “bucking,” “banging,” “kicking” or “hopping.”

An independently suspended, driven axle shaft set in which the axle shafts are asymmetric with respect to each other, wherein the asymmetry provides mitigation of powerhop. The axle shafts are asymmetrically selected such that the relative torsional stiffness therebetween is different by a ratio substantially between about 1.4 to 1 and about 2.0 to 1. The asymmetry may be provided by any known modality that alters torsional stiffness and is compliant with operational load demands of the axle shafts, as for example the axle shafts having the same length, but differing cross-sectional diameters; or by the axle shafts having the same cross-sectional diameters, but differing lengths; or a combination thereof."

May explain why the part numbers are different for each driveshaft on the M2...