Lotus Elan

Drive train weakness and rear vibration

PostPost by: jimj » Thu Aug 04, 2016 9:32 am

There was recently a thread on rear vibration but, as usual, the search function doesn`t. Any road up, as they say in Yorkshire, I, too, had an annoying zzzzzzzzzzzzzzzz last week but when lifting off the accelerator at over 70 mph. A check around the obvious, the diff. and the four bolts attaching the flanges on the diff. and the propshaft weren`t loose, but could be rotated. I`ve nipped them up and all is well.

But, my question is this; we hear about output shafts twisting or even breaking under load but, surely, the weakest point in the drivetrain would be these 4 bolts, wouldn`t it? especially if they`re not really tight and no longer clamping the 2 faces of the flanges really tightly together.
Jim
P.S. I`ll be renewing these high tensile bolts with spring washers, nyloc nuts, and Loctite, with Loctite on the faces of the flanges too.
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PostPost by: rgh0 » Thu Aug 04, 2016 9:50 am

Those bolts are not a problem as long as the bolts are tight and the flanges are clamped firmly together. The flange carries the shear load the bolts carry the tension load that creates the compression to carry the shear load.

You should not need spring washers or loctite just high tensile bolts and good quality nyloc nuts that are correctly tensioned and they should never come loose.

The output shafts are highly stressed compared to the inlet flange due to the gear ratio of the diff and smaller diameter of the output shafts compared to the input flange. The poor steel used in the original Lotus output shafts do twist and fail. The later shafts from around 1970 had a bigger diameter shank but more importantly stronger steel and I have never see one of those fail.

cheers
Rohan
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PostPost by: jimj » Thu Aug 04, 2016 10:38 am

Thanks Rohan, I was hoping you`d reply. You`re my hero, especially as you`ve confirmed what I was thinking.
Jim
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