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Author Topic: R1200GS - drive shaft, why universal joints?  (Read 3535 times)

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Offline DeepBass9

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Re: R1200GS - drive shaft, why universal joints?
« Reply #20 on: May 04, 2016, 12:50:45 pm »
Also people with 4x4s who jack up their suspension to dizzying heights also run the risk of buggering up either the drive shaft or gearbox.

Yes. Some of the extra high lift kits come with adjustable trailing arms or offset bushes or whatever is needed to correct angles etc. depending on suspension setup.

And the cheapies just have a few rubbers and longer springs....

Offline TheBear

Re: R1200GS - drive shaft, why universal joints?
« Reply #21 on: May 04, 2016, 07:06:42 pm »
Was chatting the other day and we wondered why they use universal joints on the drive shaft and not CV joints. Probably a cost thing, but would there be any other reason?

I am not sure, but CV Joints are much more expensive and their advantage is they allow more movement than universal joints.  Why use them then, when a universal will manage the movement?

If I can get a CV small enough I'll change/modify  to CV.

Why?
Well, a universal joint does not have constant transfer of power, so a CV is more efficient. Only reason, we were just wondering.

I didn't know that.  Thanks.  Will it make a marked difference?
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Offline eberhard

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Re: R1200GS - drive shaft, why universal joints?
« Reply #22 on: May 04, 2016, 07:30:57 pm »
https://youtu.be/gmV4qwLfOMY


Watch this short clip and see how much the output velocity oscilates even with a relatively small input angle. The relatively small output oscilations gets amplified hugely to the outside of the wheel when the 2 UJ's do not run exactly at the same angles and even then the drive shaft will accelerate and decelerate continiously.

And yes, the two UJ angles on the Paralever are seldom at exactly the same angles so there will always be a velocity difference at the wheel.

A CV will eliminate this. Overkill and unnecessary  maybe according to BMW but it would be nice to have a replaceable CV enstead of a UJ.

Don't know how to post the actual video

Very informative video clip. Thanks for linking it.
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Offline OomD

Re: R1200GS - drive shaft, why universal joints?
« Reply #23 on: May 04, 2016, 09:24:40 pm »
Was chatting the other day and we wondered why they use universal joints on the drive shaft and not CV joints. Probably a cost thing, but would there be any other reason?

I am not sure, but CV Joints are much more expensive and their advantage is they allow more movement than universal joints.  Why use them then, when a universal will manage the movement?

If I can get a CV small enough I'll change/modify  to CV.

Why?
Well, a universal joint does not have constant transfer of power, so a CV is more efficient. Only reason, we were just wondering.

I didn't know that.  Thanks.  Will it make a marked difference?
Well, based on the excellent video clip posted earlier it makes a difference if the 2 universal joints of the shaft are not correctly phased. Which got me wondering about the ever-present vibration (in sync with the rear wheel speed) when the suspension is set any higher than "rider only" mode. But then, I don't suppose the phasing must be exactly 90 degrees, so even if one opens the shaft assembly and inspects the shaft it would probably be impossible to tell if it is correct or not just by looking.

It is strange though that my previous GS (2008 model) didn't have this vibration that I could remember, when setting the suspension higher. If it did have it it is certainly not as pronounced as on the LC. And, both my LC and my current LC GSA both have the vibration. Which Bavarian say is normal.
 

Offline Sláinte Mhaith

Re: R1200GS - drive shaft, why universal joints?
« Reply #24 on: May 04, 2016, 09:52:54 pm »
Which Bavarian say is normal.

Get them to put that in writing.  ;)

Don't put too much trust in them saying it is normal.  They also told me something is normal but then I asked him how can it be normal if the play is almost three times more than what their manual say is allowable. Got met with a blank stare.