Paralever U-joint phasing

[PETDOC]

On another thread an owner of an '04 1150 GS Adventure was told his drive shaft was 60 degrees out of phase and to fix it would require replacement. Apparently at some point the smaller inner shaft rotated within the rubber bushing inside outer portion and then re-set. I've never heard of this. Anyone have experience with this phenomena?

I've subsequently learned the Adventure drive shafts have a flat key in the splines that prevents reassembly out of phase. My non Adventure '04 GS does not.

Seems if this is true that it would happen often to bikes that were wheelied or had the rear brake applied suddenly.

[dirtrider]

Afternoon PETDOC

 

Personally I haven’t seen the rubber dampener twist more than a few degrees on the 1100/1150 BMW but have seen more than few in the automotive world twist 30°-40° or so. Usually on the BMW when they let loose you quit moving and the shaft just spins at the rubber. But if an automobile can twist that rubber so could a motorcycle.

 

I have pulled quite a few apart that were not phased as you would think they should be but the BMW service manual doesn’t even address clocking the phasing at re-assembly. Phasing only works if both ends have close to the same working angles through most of the travel (BMW doesn’t). In fact some automotive applications offset the phasing due to non similar working angles or lateral offset of the shaft ends.

 

[PETDOC]

So D.R. if you owned the GS with a 60 degree out of phase drive shaft and it worked fine (no vibration) would you replace the drive shaft or just ride it?

[dirtrider]

Evening Again PETDOC

 

I would pull the shaft, then look VERY closely at the rubber to metal for signs of previous movement. If I couldn’t see any obvious signs of movement or delamination I would paint a white stripe down the shaft to check for any new movement then go ride the dickens out of the bike.

 

I wouldn’t have any problems using it for most riding but would probably put a new shaft in before riding to parts of the world where help might be days in showing up.

 

[PETDOC]

D.R.

Thank you for your thoughts on this issue. I find the whole concept of the independent rotation of the back portion of the drive shaft interesting. I have a non Adventure '04 GS which does not have a keyed drive shaft. Whenever I remove and reattach the final drive I merely shine a light up the paralever housing and rotate the aft portion of the shaft then reattach the rear in phase. I now assume, therefore, my drive shaft may have rotated in the rubber bushing and I never knew it.

Perhaps ignorance is bliss.

[dirtrider]

Evening Again

 

I don’t even know how close BMW controls the phasing. If you look at some of the later 1150 (keyed) drive shafts that can only go together one way even with the key controlling the phasing the front and rear joints don’t line up in perfect phasing even on brand new unused shafts. .

 

I have pulled some early (non keyed) final drives off and they were not even close to proper phasing from the factory.

 

 

 

 

[Peter Parts]

There are two aspects, the rubber bush (I sure wouldn't use one one once a shift starts, but just my gut feel) and the two u-joint splines.

 

Being a nut for boxer balance, it seems to me to be really decrepit to have drive shafts with misaligned phasing. Yet rumor is that the BMW factory has sometimes paid no attention to it assembling the bikes. Might be a mysterious source of vibration on some bikes.

 

One thing that puzzles me is that BMW has the same Paralever geometry but has different reaction strut lengths on different models (at least for the "below" strut older models). Isn't there a correct angle and hence only one correct reaction strut length?

 

Other than getting a friend to eyeball from 20 feet away, how to tell when Paralever is straight/neutral alignment? But shock absorption isn't symmetrical?

 

Ben

 

 

[Joe Frickin' Friday]

One thing that puzzles me is that BMW has the same Paralever geometry but has different reaction strut lengths on different models (at least for the "below" strut older models). Isn't there a correct angle and hence only one correct reaction strut length?

 

Other than getting a friend to eyeball from 20 feet away, how to tell when Paralever is straight/neutral alignment? But shock absorption isn't symmetrical?

 

The theoretical ideal is to have the gearbox output shaft parallel with the final drive input shaft; this will provide perfectly smooth motion at both ends of the driveshaft. Small deviations from parallel will introduce small deviations from smooth rotation, and this is part of why the rubber coupling is present in the driveshaft. Large deviations from parallel will make a mess of things, but within the range of angles that BMW employs on their bikes, it's not a problem.