R1100RS driveshaft twist - Impending failure or to be expected?

[Christo]

Recently when I was swapping out the transmission on a '95 R1100RS, I noticed painted lines along the driveshaft that weren't in alignment anymore. I can't recall the angle of twist but let's say 40 degrees. And like others have mentioned, this could be the final position after multiple 360 degree twists for all I know.

 

I never felt any vibration from an out-of-phase shaft, or slip (other than when the clutch gave out last year, which was replaced). There was one time I did a mild 'launch' at a light to get a jump on a car before a turn, and I thought the rear tire spun a bit. Perhaps that was the shaft?? That was months ago with nothing like it since.

 

When reassembling, I was careful to phase the u-joints correctly, but I'm now worried about the twist as I plan for a very long trip (SaddleSore 1000)

 

I know the general consensus is to replace, but does anyone have some experience using obviously twisted driveshafts for miles and miles with no trouble? (aside from possible vibration)

 

(I guess I don't fully understand the purpose of the rubber, or the mechanism of connection between the rubber and metal, or why there isn't a more fixed connection.)

 

[dirtrider]

Evening SnakePliskin

 

That rubber shaft isolator is to provide torsional dampening. It works & lots of vehicles use rubber isolated drive shafts.

 

If you are SURE that your shaft has migrated on the rubber isolator then you are looking at total failure in your future.

 

That rubber is bonded & once it slips there is no re-bonding it.

 

If the rubber is just twisted then no problems but that is usually WAY under 40°.

 

As far as U joint phasing, on the BMW boxer it is not all that important as both ends of the shaft don't operate at the same working angles so even out of phase results in very little shaft disturbance or vibration.

[Christo]

Thanks D.R.

 

Let's say that those painted lines indicate twist. What's going to happen next, more and more twist at lower throttle? And I wonder how long that will take.

 

Also, if I buy a second-hand shaft online, is there any way to determine if a shaft has twisted? (aside from painted lines)

[dirtrider]

Evening SnakePliskin

 

Let's say that those painted lines indicate twist. What's going to happen next, more and more twist at lower throttle? And I wonder how long that will take.--- If it IS twisting (very far) that means the bond between the rubber isolator & the shaft is slipping so next thing that happens is total slippage & a walk home. Once it lets go you are done riding the bike.

 

Also, if I buy a second-hand shaft online, is there any way to determine if a shaft has twisted? (aside from painted lines)--- Not really unless it was marked, or the U joints were phased at one time & now they are not even close.

 

That 40° twist you seem to have bothers me-- they seldom twist that far without total failure so I don't know what is going on there. Can you see the rubber bonding coming loose at all? (looks like a poor bond)

 

 

[Stan Walker]

For what it's worth. I have a brand spanking new driveshaft for an R1150RT in my possession and there are no white lines on it. Now I know it's a different model so it may not mean anything.

[Christo]

Thanks for the tips!

 

I looked through all my photos and could only find one photo of the side of the shaft, and can only see one of the painted lines. The other presumably is at least 90 degrees around. (I recall there being two lines)

 

I looked closely up inside the shaft to see where the failure occurred, and could not discern any visible tearing, crumbling, or looseness with the rubber to metal connection. It looked tight. At the time I reasoned that it was simply a tight fit and the rubber twisted under heavy load or a 'launch'.

 

Sadly, I don't recall the phase of the shaft before removal.

 

And I did a 10 mile test drive after replacing the tranny and it rode great. No slipping. (Not to mention all the miles I put on before replacing the tranny). In fact, I've put about 5000 miles on the bike since doing that launch start last summer. But some hard 2nd gear shifts since then.

 

[AndyS]

I guess for peace of mind, you will have to do a bit more aggresive riding and eyeball those datum lines again to see if there is any change.

But, as DR has pointed out, if it has moved that far already it is of great concern.

Now you have made yourself aware of this, it may be prudent to be pro active and make the change.

 

[kalali]

I didn't think it was even physically possible for the isolator to rotate that much without complete separation and failure, especially on a 20 year old bike.

[Christo]

Stan, I believe the lines are painted on during some service and not at the factory.

 

Thanks Andy. I was thinking about testing the waters before heading too far from home.

 

Here's a link that shows a failing axle. Mine didn't look like this. Mine look more like new:

http://www.bmwlt.com/forums/k1200lt/70762-clutch-drive-shaft.html

 

DR, I found this great link discussing rubber shaft failure and converting over to solid axles. Something I was thinking about

http://advrider.com/index.php?threads/airhead-paralever-driveshaft-phasing.272481/

 

[Christo]

kalali, I'm still new so I certainly don't know. But my feeling on it is as follows: My R1100 only has 40k and I don't believe it has been abused, except by my hard 2nd gear shifts So I have to wonder how little it takes to twist one of these axles? If you set out on a long trip and apply one N-m of torque too much and cause twist, is the axle going to shortly fail? In that case, everyone should drive around with a tools and spare axles. I know the Iron Butt folks sometimes take extra axles.

 

The link above gets into the reason for axle failure. As DR pointed out, the angle of the shafts and u-joints matter. Some in this thread suggest that when the axle twists, it alters the phase, which in turn increases stress, which then beats up on the rubber more, more twist, more stress,...failure.

 

In any case, I'm looking for hard data on how long a severley twisted axle has lasted. Sounds like it depends on the bike (airhead vs oilhead, monolever vs paralever, reason for twist failure, age of rubber, etc). With the fresh paint lines on my axle, perhaps it was a replacement before I bought the bike, and perhaps I should order another one just in case.

 

I like what one poster did: Have an spare axle in a FedEx box at home ready to overnight. That, or find a place to mount an extra axle on your bike. Hey, how about in place of the charcoal canister??

 

[dirtrider]

 

DR, I found this great link discussing rubber shaft failure and converting over to solid axles. Something I was thinking about

 

 

Morning SnakePliskin

 

The downside of a solid shaft is gear tooth hammering & low RPM shuddering as the torsional dampening in the drive shaft is gone.

 

The real answer is to have the rubber dampening but to also have a wind-up limiter (like a hole on the front shaft & a pin in rear shaft that fits in the hole. Obviously you want the hole much large than the pin so the rubber isolator can work but at full torque or IF the rubber should separate then the shaft can still drive through that pin.

 

OR-- a set of fingers on front shaft that interlock with fingers on the rear shaft with enough clearance in the finger interlock to allow the rubber to work & isolate.

 

 

I'm still having problems with the fact that your shaft twisted 40° but the rubber hasn't let go yet (make darn sure it HAS twisted 40°) -- Is it possible that someone has removed that shaft at one time then marked it but didn't reassemble it back to the marked line??? Remember there is an above average chance that the U joints were not phased at the factory.

 

[Christo]

DR, you and I are thinking alike! I too thought of the pin through the axle, then a larger hole/smaller pin so some damping could occur (I wondered about reduction in torsional strength with drilled holes), then a welded bracket to accept some degree of slip but still let you drive home.

 

I weld, so I thought of trying to fashion something that did not add significant weight or introduce vibration. I then thought about modeling pieces and having them cut in bulk and perhaps doing this for others, like Joe Friday's fabricated parts. Has this been done?? The idea of a 'limp home' system seems like something BMW should have done already.

[dirtrider]

Afternoon SnakePliskin

 

The pin through the holes has been used (a lot) mainly in automotive steering isolated intermediate shaft's & other critical (can't afford to completely fail drive systems)

 

The downside to a pin system in a drive shaft is it would have to be one very hearty pin to not bend or break under drive load.

 

The finger (or notch) system could handle more torque but would be much more difficult to implement.

 

One of the BIG problems is: any welding on the shaft near the rubber isolator is sure to weaken the rubber-to-shaft bond.

[Christo]

This is fascinating stuff. Yes the pin would have to be pretty stout. Good point about the heat of welding.

[Stan Walker]

It seems to me you have two choices:

 

1) Gamble with the one you currently have. Who knows what the white lines really mean! It's pretty low mileage for a failure. Maybe add some RED lines and check it later to see if it really is slipping.

 

2) Replace it with a new one. A used one doesn't cut it as it may be worse than the one you have!. It's just money, it grows on tress, so I hear.

 

I'm going with option two. My '02 RT drive shaft has 134,000 miles on it and MAY be perfectly good (don't know, it's still in the bike). I'm replacing it anyway, that's why I have a brand new one sitting on my work bench. The old one will be inspected and kept for a spare if still OK.

 

I think I will mark the new one with white lines. Might even check it a few years from now.

 

Stan

[Christo]

Hello Stan, thanks for the comments. That's great mileage with your original part. And it sounds like you're covered in case of a problem. I probably would have done the same thing if I had gotten that many miles out of the original one.

 

As of your posting, I had already ordered a used drive shaft on eBay. It was advertised as low miles. I plan to thoroughly inspect it, and return it if it looks to be a problem. So I guess I'm splitting the difference between your two suggestions.

 

Logic would dictate that the donor bike was not salvaged because of the driveshaft, so the driveshaft was probably OK. If my drive shaft has a 50% probability for failure and the used one does as well, does that mean that I have the equivalent of a new one?

 

I'm now trying to decide whether to carry the extra drive shaft and certain tools with me when I head out for my long trip, or leave it in a place that it can be overnighted. About tools, and thinking I could probably find an Advance Auto wherever I am and get tools. I need to read up on what others have done on long trips

 

[Dadrider]

There is no one in the BMW world that overhauls or zero times these driveshafts? New replacement or finding used are the only R&R alternatives?

[eddd]

There is no one in the BMW world that overhauls or zero times these driveshafts? New replacement or finding used are the only R&R alternatives?

 

There are companies that will install new and serviceable u-joints, but there is no way to address/renew/replace the rubber dampener. That being said, a rubber dampener failure is pretty rare.

[Christo]

Hello all.

 

I wanted to provide an update on this discussion. To summarize I had indications that my drive shaft had twisted by at least 40 degrees according to some paint marker lines that were now out of alignment by that much. I was having no slipping issues, but I wanted to know what the likelihood was of a failure if I kept riding on it. I purchased a backup but have not installed it yet.

 

2000 miles later and still no slipping. And I ride normally with hard second gear shifts an occasional hard acceleration. No launching.

 

I'm now planning a multi-hour trip with my wife for the first time on the back and I'm worried about it again. I would replace it now, but don't have the time. I'll be within towing distance if the worst happens.

 

My question:

Is there anyone on the forum that has experienced a drive shaft twist while on a trip ( and it was drive shaft twist for sure, not a clutch) and still been able to ride home?

[dirtrider]

 

My question:

Is there anyone on the forum that has experienced a drive shaft twist while on a trip ( and it was drive shaft twist for sure, not a clutch) and still been able to ride home?

 

 

Morning SnakePlisskin

 

Those drive shaft rubber dampeners can twist a bit & the shaft will still live a normal life BUT once the bond between the shaft & the rubber dampener breaks you will not ride it home with that shaft in the bike. It will not repair itself or rebound, once it starts actually sipping you are done.

[Christo]

Thanks again DR!

 

I trust your opinion so I'm now thinking that perhaps my drive shaft was not as damaged as I suspected. I can't explain the misaligned markings on it, but that was 2000 miles ago, so I'm thinking if it were in a failed state, it would have exhibited some signs by now, according to what I'm hearing.

 

I won't venture more than 200 miles from home before swapping out this drive shaft, just to be safe. The one I bought online looks perfect with no signs of the rubber being molested.