Phasing driveshafts

[Me-109]

So ..... I've had the back-end stripped to replace the gearbox output shaft oil seal and I've rebuilt it ok. Actually I only think I've rebuilt it ok, since I came across some info in amongst the paperwork I got with the bike to do with replacing the paralever bearings. The info was a printed download from http://www.bmw-motorrad.co.za/default.html but the particular item (Final drive R&R) is no longer listed, though there is an interesting Workshop section here now.

Anyway the bit that caught my eye suggested that on rebuilding the driveshafts they should be 'phased', that is that the UJs at the gearbox end and the final drive box end be matched, say with they outermost joints in the horizontal plane and the driveshaft joints in the vertical plane.

Having read it several times it suggests that the driveshaft will only go back together one way, such that getting them out of phase is not possible.

Now I didn't pay that much attention to this when I rebuilt mine, though I sort of set them out like this anyway. A little bit of fiddling on reassembly got the final drive lined up and slotted in ok. Now it's built I can't see the alignment of the rearmost UJs because of the depth of the final box into the swingarm, even if I could see the front UJ by pulling back the gaitor. I don't remember any of the splines looking slightly wider or thinner to ensure single-plane installation.

So my question is - Could I have reassembled the driveshafts incorrectly or do they indeed only go back together one way?

Ok, second question - if there is no single way to assemble them, would incorrect phasing introduce vibration (not felt any) or potentially stress the bearings and UJs?

[adamski49]

Try this thread.

Phasing done to death, not sure of the outcome though. Some say it does matter and others say not. Confused? You will be.

HTH

Adam

[Boxadog 2000]

Take the word of someone who has fu**ed up, they will go back together any way there is no master spline (thank yo very much mr BMW).

They must be phased or in the same plain and not 90 degrees rotational.

IE the uj at the gearbog end MUST be the same as the uj at the bevel end.

I didnt and I shagged my final drive.

Bob

[Jason M]

Take the word of someone who has fu**ed up, they will go back together any way there is no master spline (thank yo very much mr BMW).

They must be phased or in the same plain and not 90 degrees rotational.

IE the uj at the gearbog end MUST be the same as the uj at the bevel end.

I didnt and I shagged my final drive.

Bob

And just to be contraire, I've had mine appart at least 7 or 8 times and never phased it - the bikes now done nearly 135K and the final drive is still OK

But Bob is an engineer, and I fix things like a farmer, with a big f**k off hammer, bailing twine and tape

You pays your money....

Jason

[MG]

I agree with boxerdog, they should be phased correctly. I found this out the hard way after lubricating the paralever bearings, lining it up as best I could, bolted it all together, took it up the road and it didn't feel right. at exactly 49 mph there was a harmonic vibration. harsh enough to be noticable and if left would have wrecked the uj's, bevel box and maybe the transmission as well. Had to do it again with a bit more care. It's basically a crap design, there is no master spline and to make matters worse you can't engage the splines until the shaft is almost out of sight. If you are doing it yourself just take your time, its not difficult, only very fiddly.

Mike

[bigblackfalco]

Take the word of someone who has fu**ed up, they will go back together any way there is no master spline (thank yo very much mr BMW).

They must be phased or in the same plain and not 90 degrees rotational.

IE the uj at the gearbog end MUST be the same as the uj at the bevel end.

I didnt and I shagged my final drive.

Bob

And just to be contraire, I've had mine appart at least 7 or 8 times and never phased it - the bikes now done nearly 135K and the final drive is still OK

But Bob is an engineer, and I fix things like a farmer, with a big f**k off hammer, bailing twine and tape

You pays your money....

Jason

the prase 'twatting device' springs to mind!
Ditto the theory;had mine apart more times than i can remember(in 125'000 miles),never phased at all.If it is so important,why no locating pin/mark etc??
Bailey.

[Me-109]

Well I felt convinced enough from a mechanical sympathy perspective to go back in and have a look. I'd done about ten or fifteen miles after the first rebuild at up to the legal limit ( ) and hadn't noticed any additional vibes, but figuring harmonics could wreck the UJs over time, I thought it worthwhile, especially as no added cost was involved, just time.

As it happened I wasn't far out with the first install, say 25 degrees. At least I got to check for any lost oil whilst I was in there!

Typically it took about twenty minutes of fiddling trying to get the things lined up right to get it to slot home this time round. Those boxes get heavy after a while!

All in all, it took about another two hours, but half of that time was probably spent cleaning, greasing and faffing about getting the shafts back together.

I think the biggest fear with unphased shafts is that when 90 degrees out of phase the articulation could lead to one UJ coming into contact with its opposite part whilst the suspension still moves the other end ever higher. On the S I doubt if the range of movement is ever that large to make that a reality. Perhaps on a half-shaft of a 4WD or tractor, but not in this application.

Thanks for all opinions, whichever side they were on.