The picture posted below is of two different Audi 01E input shafts. The pictures came from
Charlie Smith's 01E web page. The input shaft at the top of the picture is referred to as the "standard" shaft configuration, and the lower piece is referred to as the "necked down" shaft. Charlie Smith explains the differences between the input shafts as follows:
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have recently found that the higher torque engine applications had a necked down mainshaft that would flex a little bit, thus keeping sudden torque impacts from loading the gear surfaces quite as much. Here are pictures of both types of mainshafts . Please note that the description "flexible 1st" is talking about the necked down versions of the mainshaft, which would permit a bit of "wind up" upon sudden torque load. Thus this main shaft was acting like a torsion bar spring in a suspension.
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I disagree with his analysis. It appears to me that the necked-down input shaft was not designed to twist under torsion so much as it was designed to reduce stress raisers. Having devoured Carroll Smith's
Engineer To Win a few times, I would say that the ultimate strength of the input shaft (metallurgical differences aside) is determined by the root diameter of the splines, and that the abrupt diameter increase just to the right of the splines and again a couple inches to the right are classic stress raisers. Accordingly, I would say that the input shaft at the bottom of the picture is stronger even though it is smaller and probably lighter.
My question to those who are more experienced in mechanical engineering is, "how much better?" Is my analysis off the mark? Any feedback is appreciated.
BTW, the reason I ask is that I am considering buying a used 01E transaxle that uses the standard shaft. I expect the price to be good, but I wonder if I should hold off for a box with the improved input shaft.
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