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The design of these propshafts and how they are fitted does not compare favourably with common driveshaft / propshaft knowledge.
(Let the lecture begin!)
This system relies on everything being in line - once you've got that idea fixed in your head the planets start to align and problems can be solved!
Think of an imaginary line that runs from the front of the engine at the crankshaft pulley that runs along the centre line of the crank through the centre of the flywheel - through the centre of the transmission - through the transmission yoke - through the flex discs - through the centre propshaft bearing - through the input yoke on the differential and out through the differential pinion...
...this imaginary line needs to be a straight line - it needs to be constant and unwavering in the vertical (y-axis) and the horizontal (x-axis) => this line needs to exist only in the z-axis (one dimensional)...
...the existence of a single universal joint is misleading. This needs to be set in the straight - zero degree - no bend position to stop any inherent induced vibrations. This configuration is less than ideal for a universal joint as it encourages "flattening" or Brinelling of the joint. All Mercedes UJs in this set up will end up being notchy.
The effects of a notchy UJ are amplified when this imaginary line - the alignment between each part of the driveline - is not just quite right.
The message is:
Consider the relative heights and positions of each resilient component of the driveline. Motor mounts at the front - transmission mount at the back - centre propshaft bearing - differential / subframe mounts at the rear. If one (or more) of these heights is not aligned with the others then you get a bend in the propshaft <= And in this system it should not happen!
(in addition to the resilient mounts flexdisc health is important)
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