Propshaft White Dots and Phase

[LGK6D]

Hi All,

So last year I bought a very low milage car which had been fitted with a replacement fuel tank. The car in itself is mint, but it had a vibration which started at 60/65 and couldn't be driven through. I checked all of the straight forward stuff and worked my way around to the prop shaft. I found that the factory white dots were mis-aligned by one spline. No drama, I've set the proshaft up with the dots perfectly aligned on my work bench, but I've noticed that the universal joints are very slightly out of phase, I've measured it at 5 degrees. According the the Bentley manual it should be perfectly aligned. If I rotate the rear half so the white dots are 180 degrees out of alignment it's only 1 degree out. What's the story here?

Many thanks
David

[Brianmoooore]

Two halves from two different prop shafts?

[LGK6D]

Hi Brian,

No, I can’t see it. The car is very very original and the condition of both halves match. It looks like they dropped the rear half just to get the tank out. The Guibo bolts were untouched and the exhaust front pipe had never been off.

[Brianmoooore]

The plane of the joints lining up should take preference over the white dots.
There's only two ways a prop. can go back together correctly, and that's the right one, and 180 degrees out. The white dots are really only to ensure the right one of the two is chosen, although they do normally line up fairly well.
Bit from two different props would explain both the imbalance and the misaligned dots.

[LGK6D]

Okay, so I’ve measured it up again, 180 degrees out seems perfect and does actually measure 0 degrees difference, but with the paint dots aligned it’s out by 5 degrees. Am I to suspect that the paint is not from BMW?

Did BMW balance both halves of the shafts independently or together as a unit?

[paultv]

My "dots" were round indents stamped into the metal, but not white or painted - hard to see - look for these- just a thought.

Paul

[Brianmoooore]

Always been white painted dots on every BMW prop. I've been involved with, not just those on E30s. I suspect any stamped marks have been put there by a mechanic at some time.
Prop. shaft was balanced as a whole assembly by BMW - that's why you can't mix and match.

[LGK6D]

It’s looking quite likely that at least one of these painted marks is in question. I’ve counted the splines out at 27, so divided by 360 degrees gives us 13.333 degree change per spline. Looking at the prop shaft as a unit, there is only one way it can go together and if that’s the case, would it not have been marked at all?