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Old 10-03-2007, 11:10 AM   #1
chiefrider OP
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Airhead Paralever driveshaft phasing

My 1993 R100GSPD, Rocinante, has taken me to school on this issue.

About 20 months ago, while preparing to ride to Alaska and Prudhoe Bay with my brother & my nephew (my greatest ride EVER), I swapped the driveshaft with one that had fresh u-joints. I pulled the still seemingly good driveshaft out of bike when I installed the rebuilt unit. The bearings on the old shaft's u-joint felt nice and tight.

I made it through the last two summers and one winter without problems on the rebuilt shaft.

A few weeks ago, the bike had that "clunk," and I pulled the driveshaft out. The front u-joint had shed it's bearings.

I inspected my old driveshaft and the one I had just taken out of the bike. I put them each in a vise and checked to see if the the front and rear u-joints were "in phase," meaning that the u-joint's "U's" that are fastened to the shaft body/rubber damper assembly, are parallel. I put small straight-edged rulers on these pieces and a visual inspection showed BOTH shafts had their u-joints about 7 degrees out of phase.

CONSTANT VELOCITY (CV) joints have their input & output sides running at a constant velocity with each other regardless of angle (thus the name). Airheads tech guru Oak Okleshen, was working on a CV joint retrofit for the early paralevers, but development costs (and perhaps projected product liability costs?) have indefinately stalled this. Understandable, considering how small of a market for such a conversion would be.

U-JOINTS, with constant-speed inputs, have small accelerations/deaccelerations when you run them anywhere except at zero angle, and those accelerations/deaccelerations increase as you increase the angle of the bend. Unlike the driveline u-joints you find on rear wheel drive cars, the Airhead Paralever u-joints run at a rather extreme angle, thus greater accelerations/deaccelerations.

Having the u-joints in phase, or in alignment, minimizes the affects of these accelerations/deaccelerations. Likewise, an out-of-phase shaft has the u-joints "fighting" each other, and beating that poor rubber damper like a red-headed stepchild with each rotation.

The natural rubber damper in the driveshaft between the out-of-phase u-joints breaks down from the added stress and the shaft twists even more, pulling it more out of phase, which adds more of the hammering stress, which then pulls it even more out of phase...a cascade effect, mind you.

I am now of the belief that simply replacing the u-joint bearings and not addressing the phase issue is throwing good money after bad.

OPTIONS:

ANOTHER BIKE--and lose the otherwise owner-friendly panache of this wonderful airhead. An giving up Barley Therapy.

NEW BMW DRIVESHAFT--expensive, but will give you a servicable life for, what, 20,000 to 40,000 miles? At this point, a chain drive begins to sound real good, validating the first option.

SOLID SHAFT--but if the miserly BMW bean counters at the time were willing to risk catastrophic transmission failure by leaving out that lousy $.85 circlip, how could they justify the expensive, rubber-dampened driveshaft assemblage if a simple piece of metal rod would work in its place? That rubber damper has a purpose, perhaps to protect the final drive or transmission. Heck, my Honda CL90 has a rubber "cush hub" between the rear sprocket and the hub to protect the driveline from the titanic forces that wee thumper, no doubt, unleashes. We're dealing with about 10 times the power with the Airhead driveline from the 90. I am skeptical of the long range utility of the solid-shaft solution. Anybody have any real information, data or experience on this?

REPLACE THE DAMPER--this is the solution I am pursuing. Guy Henderson (209-962-7500 guy@hendersenprecision.com) pulls out the worn natural rubber piece and replaces it with one made of urethane rubber of the same durometer, which, according to Guy, should stay in phase about 3 times longer than the stock, perhaps 90,000 miles? Cost, currently, is $175, for this urethane piece installed. He has more info in the advrider vendor forum.

Link: http://www.advrider.com/forums/showt...haft+confusion

It doesn't hurt that Guy is an Airhead GSPD AND an Indian rider (a fellow after my own heart!).

Thoughts, fellow Airhead GS'ers?
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Old 10-03-2007, 12:07 PM   #2
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I think that up till the recent shafts they were all solid, and were better known for longevity.
I think you make pretty valid points to ponder, though.

I was taking a long look at my shaft the other day (no jokes, please )

and it almost seems like not only is it not a straight line horizontaly/longitudinally from the output shaft to the rear diff, but transversely, as well. that is: I think the shaft is further outboard at the rear than at the transmission. Is this true, or am I sniffing too much fork oil?
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Old 10-03-2007, 01:45 PM   #3
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Hi, Stagehand,

I believe all Airhead Paralever shafts have the rubber damper assembly.

With the shaft out of the bike and in the vise, with the jaws gripping the outer damper body and sitting horizontal, look from the splined end (rear) towards the front. If the shaft were operating in the bike and you were able to view it from this angle, the shaft would be turning in a counter-clockwise fashion.

I'd wager a half a peach that your front u-joint, viewed from this angle, is rotated a little bit counter-clockwise, as if the wheel and rear drive were locked up and the transmission output shaft spun and compressed the rubber a little bit.

Which, in fact, isn't too far off the mark.

When the bike is operating, pushing 700 to 900 lbs. of bike, rider(s) and luggage, there is constant pressure on that rubber, and the rubber just gets tired. And the driveshaft creeps out of phase, which introduces a light hammering on top of that running stress, which accelerates the wear on the rubber, which, puts it more out of phase, and the hammering intensifies, and so on, until the shaft is so out of phase those poor little u-joints can't handle it anymore.

I had the tranny out last July (broken shift spring, but had the box rebuilt with new bearings, seals and circlip by Steve Prokop in Dundee, OR), and both I and our celebrated Oregon Air Marshall, Garry, did the reassembly. We both looked over the driveshat at that time and both of us deemed the bearings to be tight and fit for duty. That just two months prior to the u-joint's failure.
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Old 10-03-2007, 02:30 PM   #4
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Nice write-up.
It a damn wonderful design isn't it.

I like a good O-ring chain more all the time.
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Old 10-03-2007, 02:39 PM   #5
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Tom,

Up until 1981 all beemers had a solid driveshaft. That includes the R90S and the R100RS - two of the most hot-rodded airheads. They didn't have u-joint failures or trans or final drive problems. But then again, the shaft rode in a bath of gear lube so the joints never went dry. But you get my point.

What would be interesting to know is how the GS'd twin shock models fared. Did their lengthened, oil-bathed shafts have u-joint problems? Do they have trans or final drive problems.

Then in 1981 BMW added the cush to the driveshaft. But... mind you, the transmission has always had one on the output shaft, so the trans is protected, and I'd guess it also protects the final drive. So why TWO cushes?

I've removed the cush (because I don't like it) on the 84 I've got and it caused no problems.

One thing you left out was that Eric Dement in Germany has built some shafts for himself and a friend, and they've put something like 20 or 30K Kilometers on them with no problems.

I'm thinking that's the way to go. I'm sure any good driveline shop could modify one of these shafts to eliminate the damper. That's what I plan on doing.

Also of interest is the CV joint project. I'd heard it was shelved after one of the test bikes crashed due to a CV joint failure. Bummer - I was really hoping that one would work out.
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Old 10-03-2007, 03:19 PM   #6
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Hi, Terry,

Yeah, I had been in contact with Erich (erdemant@aol.com) the first go-around a couple years ago. I still have his letter and pictures of his modified drivesahafts. However, with the world currencies leaving pResident Bush's dollar in the dust, I'd be afraid to ask what he's want for the conversion with the euro-dollar exchange rate being what it is.

20K-30K kilometers = 12K-18K miles. Not convinced yet. That's a fairly good year for either you or me, Terry.

I've heard the monolever GSs fare much better. It's supposed to be a better tool for the 'round the world type of travels.

Regarding the addition of the rubber driveshaft damper in 1981, BMW went to a lighter flywheel that year, too. I wonder if there is a connection there. Perhaps it might be prudent to install the heavier flywheel (and old style clutch and transmission splines) if you run a solid driveshaft. I don't know.

As far as I know, NO BMW has had the driveshaft difficulties our beloved Paralever airhead GSs have. I haven't heard of u-joint problems, for instance, of the last R100R's, which is equipt with what looks to me to be the same Paralever assembly. The angle of the R100R u-joints, with the short suspension, is MUCH less pronounced compared to the long-travel suspension equipt bikes. I am fairly certain the angle of the u-joint is a factor here.

However, there were a lot less of these Paralever R100R's sold here compared to the GSs and GSPDs, so anecdotal reports of driveshaft problems are going to be, correspondingly, less frequent. Yeah, I could put on a shorter shock on my bike and lower the suspension in the triple clamps, but then, would it STILL be a GSPD?

My brother Dave gave me another definative solution to this problem: It's called an oilhead.....

Tom
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Old 10-03-2007, 04:24 PM   #7
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Quote:
Originally Posted by chiefrider
My brother Dave gave me another definitive solution to this problem: It's called an oilhead.....
The only driveshaft failure I've had (and this includes 100k miles on a PD) was on my R1100RS.
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Old 10-04-2007, 01:33 AM   #8
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The 1981-on bikes didn't have a rubber cush drive but a sort of copy of the one in the trans - a spring loaded thing that could rotate 180 degrees if enough torque was applied to it suddenly.

Those figures for Eric's mileage on his solid shaft were from three or four years ago at least. It would be interesting to contact him for current data.

And it's true we don't hear of problems with the R100R. I've heard of only one - a shaft failed and the bike went down with the rider and his passenger. This was in S CA somewhere a few years ago. Plus, I'm afraid my 100R has a driveshaft issue since it's making a clicking noise when I rotate the rear wheel. It's had some vibration for a while I've been trying to tune out, so I may have my answer. Not what I wanted to hear, though.
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Old 10-04-2007, 06:05 AM   #9
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It might be that the joints in the oil filled drive shafts run a bit cooler too - at the angle the shaft runs on the paralevers the joints must run quite hot.

When folks started racing the Datsun 240 Z lowering the suspension and changeing the angle if the halfshaft UJ s resulted in quick failure of the joints- they were getting too hot and blowing the grease out . The cure was to fit a vaned alloy spacer between the UJ and the flange on the diff/ hub, This cooled the joint enough to make it reliable again.

My local BMW guru reccommends that about 1/2 a cup of oil is put in the
" dry" paralever shafts - one of the things this might achieve is to keep the joints a bit cooler ?

The last urathane joint I had repotted cost $20 - FWD Auto specialists should be able to put you in touch with someone who does it - these big SUVs knock the hell out of their suspension bushes if the ever get offroad.
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Old 10-04-2007, 06:44 AM   #10
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Quote:
Originally Posted by Beemerboff
It might be that the joints in the oil filled drive shafts run a bit cooler too - at the angle the shaft runs on the paralevers the joints must run quite hot.
The oil bath shafts have only one U-Joint, so there's no push/pull from an out-of-phase condition.

But that raises another question - if there's no second UJoint to equalize the speed up/slow down of the Oil bath variety, why don't they go out from the stresses?
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Old 10-04-2007, 07:40 AM   #11
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Quote:
Originally Posted by Beemerboff
My local BMW guru reccommends that about 1/2 a cup of oil is put in the
" dry" paralever shafts - one of the things this might achieve is to keep the joints a bit cooler ?

.

Ha Mine does that all by itself

I still am under the possibly mistaken impression that the rear connection is further outboard than the trans connection, and I think if this is true, then the two faces of the flanges are parallel, but the shaft is at a slight angle to both. This, I believe, might exacerbate the u-joint problems the paralever has. Can anybody confirm the dogleg in the driveline, with me?

My pictures are not clear. I need to take the shock off to see it fully.
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Old 10-04-2007, 08:13 AM   #12
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Before pulling everything apart, I put Rocinante on her centerstand and got the rear wheel off the ground. I rocked the rear wheel back & forth, and heard the "clunk, clunk."

Then I put my thumb & forefinger from my right hand on the rubber boot between the swingarm and transmission, and rotated the wheel slowly with my left hand until I could feel, through the boot, a corner of the tranny/driveshaft junction. I held this firmly as to acertain the transmission wasn't moving, and rocked the wheel again. I could feel and hear that the clunking was from the forward part of the driveshaft and not the transmission (whew!).

At that point wrenches started spinning.........
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Old 10-04-2007, 09:00 AM   #13
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PD driveshafts

Other late model BMW's also have that rubber section. I don't think any of them have the rubber shaft AND the high angles of the GS. My driveshaft issues first manifested as a harmonic "beat", felt in the footpegs. I foolishly started chasing engine vibration phantoms. Shoulda' known better. Both the u-joints were still fine, but the input to output offset was at least 10 degrees. Pheh. Gimme a /5.
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Old 10-04-2007, 09:03 AM   #14
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Quote:
Originally Posted by tvrla
The oil bath shafts have only one U-Joint, so there's no push/pull from an out-of-phase condition.

But that raises another question - if there's no second UJoint to equalize the speed up/slow down of the Oil bath variety, why don't they go out from the stresses?
VERY low angles, and the driveshaft itself is long enough, and small enough diameter to act as a torsional damper. Early Yamaha shaft drive experiments resulted in a lots of carnage, because they overbuilt the shaft and it wouldn't absorb the load peaks (engine power pulses, u-joint stuff, and intentional ham-fisted shifting by the testers).
Steel is wonderful stuff. Very elastic. Makes good springs (and drive shafts too!) If anyone marketed a GS shaft without the rubber section, I'd buy one in a heartbeat.
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Old 10-04-2007, 09:33 AM   #15
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Thanks! That sure sounds right. I'm with you there - I want a solid shaft on mine as well. And like you, I've been chasing vibrations thinking it was the engine when it was most likely the shaft! And here I thought I was nearly immune with the R100R.
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