Flex disc driveline angle and phasing. Similar to U-joints?

[777funk]

See here:


https://www.youtube.com/watch?v=Idk3BVDVHq4


I wonder how flex discs are dealt with in this regard.

[Mxfrank]

A Mercedes driveshaft has no phasing issue, because the crankshaft, transmission shafts and the differential pinion are exactly in line. A small angular mismatch can occur during acceleration, due to compression of the mounts. This is taken up by the flex disks.

However, the center u-joint can pose a problem if a mount was crushed. As the engine, transmission and differential mounts deteriorate, the drivetrain alignment suffers. Since there is only one U, the irregularity can't be cancelled out, and the joint wears, as do the flex disks. For this reason, all the rubber mounts should be replaced as a set.

[777funk]

Originally Posted by Mxfrank

A Mercedes driveshaft has no phasing issue, because the crankshaft, transmission shafts and the differential pinion are exactly in line. A small angular mismatch can occur during acceleration, due to compression of the mounts. This is taken up by the flex disks.

However, the center u-joint can pose a problem if a mount was crushed. As the engine, transmission and differential mounts deteriorate, the drivetrain alignment suffers. Since there is only one U, the irregularity can't be cancelled out, and the joint wears, as do the flex disks. For this reason, all the rubber mounts should be replaced as a set.

Interesting. Thanks. That makes obvious the need to replace these wear parts for the reason you mention... So the flex discs should concentric to one another and the flat faces should be perfectly parallel.


What caused me to wonder is that I'd heard that any time you remove the flex discs, the driveshaft should be marked in its relation to the output yoke on the transmission tailshaft as well as the input yoke on the differential. I figured it was for timing of the phase angles. I guess it's for balance that this becomes important?

[Mxfrank]

I'd not heard that, and there was certainly no attempt to balance the entire system end-to-end at the factory. But if you separate the sections of the driveshaft, they should be restored in the correct orientation to maintain balance.