Hi i have an 88 r100 gs, 80k, original driveshaft. I am repacing the Tranny.

Why does the driveshaft break?
Exactly, what breaks and how can you check for wear?
What can you do to avoid the problem?
Can you over grease u - joints?

Cheers

Why they brake down?

Well excuse me, but welcome to the Real World!

Everything that moves wears. They all brake down sooner or later but how soon mostly depends on the knob who holds the handlebars, how he loves-knows-ridestyles-and-maintains the bike he rides with.

120Ks on two boxers for me and exacly ZERO problems, if you ask from me.

Nevertheless I carry FD bearing repair kit with me, takes very little space and doesn't cost much at all, it's like a separate chain-set for me, but costs a lot less and a hell lot more hasslefree way powering the rear wheel.

Trannys on some airheads are bulky tho, you should always do your homework before heading out for the big trip. I think most of hardcore airhead travellers have their trannys modded (bearings?) before heading out.

Airhead experienced travellers will comment this in detail i hope!

Yes you can overgrease u joints .
I have found that the only type of grease that is any good for universal joints is synthetic , I use Metalon grease .It works very well in the extremes of temps we get in Canada .
Synthetic gear and final drive oil is good idea too .

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Blessed are the cracked, for they let in the light. - Spike Milligan
"When you come to a fork in the road ,take it ! When you come to a spoon in the road ,take that also ."

Hi Radioactiveangel

On the BM's its crap design.
On the paralever models there are 2 UJ's, one at either end.
This shaft on the road bikes (RS/RT) seems to be ok but the gs has much more suspension travel.
This can overwork or try to "block" the action of the UJ. There is also a rubber cush in the shaft that can cause a certain amount of whip.

There are 2 problems with this shaft:
No way to grease it without stripping it.
No circlips holding the bearing caps in place.

Various people re-work the shaft to include a grease nipple at each end and to add circlip grooves to retain the bearing caps.

The standard unit has "chisseled" notches to hold the caps in place. These can wear in time and allow the cap to come out and hit the shaft casing with predictable results.

You can also loose your grease from the uj if your gearbox seal leaks enough that it "washes" the grease away... also with predictable results.

Thats why I'm getting an exchange shaft from Erich Diamant before my big trip. €325 seems to be cheap insurance.

You cant overgrease the original uj. On the aftermarket ones, I suppose its possible, but the grease will just end up in the shaft housing.

If you strip you shaft down every 30k kms, re-grease and re-peen the endcaps, there would not be any problems... in theory.

Bests of luck
Redboots.

PS. Are you still looking for a gearbox? I only know of ones in Europe though.

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Nostradamus Ate My Hamster

80k!! If this shaft is original, and your having this much trouble with your transmition, i would replace the shaft the same time you replace the new tranny. Your shaft may be okay, but the odds are against you at this point. Some people have gone over 100k with the stock shaft, but most haven't. This is a good opertunity to replace your shaft with a re-built shaft with greasable/replaceable u-joints and good rubber dampener. For the price, it's worth getting one of these. My shaft was replaced over 100k miles ago and is still in excellent shape, but i re-grease mine every 10k-15k miles. Maintinence is the key to longevity.
Make sure your rubber boots on either end of your swingarm are in good shape with no cracks. If they also have this mileage on them, they should be replaced, they are also cheap.
Whatever grease you use to lube your splines, make sure it is a moly grease. This prevents corrosion and sticks best to the metal.
Check out these links on grease and driveshafts:
http://www.advrider.com/forums/showt...ghlight=grease
http://www.advrider.com/forums/showt...ghlight=grease
http://www.advrider.com/forums/showt...ghlight=grease

...tons of info here. Also answers to all your questions

Yes thankyou Margus, i am aware of the universal law of gradual decay i wasnt asking 'why' as in 'why does it break' perhaps i should of re phrasaed the question as ' how does it break'.

I now understand thanks for the other posts ADV riders posts very helpful, especially re: shaft drive phase. I am having mine replaced anyway but will look at the original to see if any lateral movement in shaft.

I will be installing the tranny and driveshaft in Pakistan. Could somebody clarify for me exactly what grease to look for and is their some helpful sites to show me exactly where and how much.

Thanks.

Very much in the deep end.

The U-joints fail because eventually, the grease gets out past the seals and they run dry.
My experience with them, mostly street driven GS's, is that the rubber damper twists as a result of a failing U-joint binding up, not the other way around.
I rebuild my own using U-joints from a Toyota Dyna delivery truck stearing shaft. About $40 in parts.
Briefly, I burn out the old U-joints with a cutting torch and then Dremmel out the swedge marks. Then install the new joints and tack-weld washers over the end caps to hold them in place.
Details can be found at www.advriders.com. Search, "Proactive Driveshaft Repair".

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Motomech
Playas del Coco
Costa Rica

"..an attaching bike on which one rolls serenly along."
(Google translation of a French R100GS review)

I found this for you: http://www.airheads.org/content/view/226/98/
Look through the site to answer all your questions

Concur with Redboots opinion ,the design on the older paralever is flawed and it is also evident on the street models. I have experienced three such failures on a 1994 R100R , always the aft u-joint seizing up and destroying itself. The original shaft lasted 163000km and I was willing to allow it as being used up. However its replacement went a few years later at 75000km and then that one lasted barely a year before it crapped out at 27000km. This last one was the worst as it happened half-way down Baja and entailed hitching a ride back to San Diego with the bike to get it repaired .All work was done by factory trained technicians at modern well equiped BMW dealers, so it is not a question of hamfisted installations.
My theory is that one of the causes may be the aging grease . The model has been discontinued since '94 or so, and I assume that all replacement shafts were manufactured before that in one production run, including all its flaws( non- greasable ,too wimpy, too sharp angles of power input) Since then the tiny bit of grease has been decaying, using up its "half lives" so to speak, judging from the decreasing distances between replacements.
It gets very annoying paying $600US for what is basically a grease job.Fortunately at least the last one was covered by BMW's one year waranty on parts.
Here in Otario there is a machine shop in Kitchener who specialise in repairing driveshafts on BMW and all kinds of motorcycles and cars and I hear good reports about their work. See them at www.brunos.us

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93

I have gained a lot of experience with U joints on machinery over the years and have a pet theory regarding greasing .
They never wear out evenly ,usually one side or sometimes both sides of the "spider" will fail before the other , but never all 4 together .
The cups contain roller brearings ,which by their nature ,require very little lubrication , so why does one side fail before the others ?
Very often there will be rust present .

Also Sjeord comments upon the short life expectancy of the replacement units .

I think that it has more to do with the integrity of the grease seal on the bearing cup .When the rubber seal begins to fail it allows moisture to be drawn into the u joint .[It may only be a very small amount of moist air being sucked into a warm u joint as it cools down after a long ride ] But over a period of time there is sufficient water to degrade the grease in the cup and the bearing fails.
Seals can fail through old age and the effects of ozone and UV light .

The out of phase condition I personally believe is due to the u joint failure and not vice versa .

Consequently I would always grease the u joints sparingly at a regular interval [based on the useage of the bike] and always before storing the bike for any length of time .In order to do this a grease nipple is necessary ,which would require a modification .This mod impressed me :


I believe this type of mod ,other than the urethane damper , could be done by a competent machine shop anywhere if you had the correct parts to hand .
If I was going RTW ,I would have my driveshaft modified in this way and lubed with synthetic grease .


Best of luck .
Dodger

__________________
Blessed are the cracked, for they let in the light. - Spike Milligan
"When you come to a fork in the road ,take it ! When you come to a spoon in the road ,take that also ."