Having watched Crazy Frog's tutorial about why our final drives fail, I went to my workshop to look at options with the swing arm, bevel box and drive shaft.

This is what I came up with, just conjecture at the moment.

If we fitted an oil seal with 28mm id, in the end of the swinging arm, which would seal on the drive shaft, and a threaded filler and drain hole drilled in the front of the bevel box, say 10mm filler and 8mm drain, we would create a cavity of about 300cc around the final drive splines. Then 150cc of oil should be adequate to keep the joint lubricated in oil as per CF's conclusions.

I can see that the drive shaft would need to be fitted before the swing arm, against recommendations, but I've assembled it that way before so it can be done. So what have I missed?....... Would it work?....... Over to you.

Paul

Don`t know how oil resistant the rubber in the driveshaft is.
Could be that it don`t appreciate to be soaked in oil?

Inge K.

Inge K, the seal would be on the narrow end of the shaft so the rubber wouldn't come into contact with the oil.

Paul.

Reading your first post all over again.....things clear up.
Seems like a good idea....but is it worth the hassle...my oldest one have passed 200K km....
the swing arm has never been dismantled.

Inge K.

I don't know if you could run a seal at the upper part of the shaft. It would depend on how much the shaft deflects after the uni joint.

A short grease nipple into the cavity above the shaft and a threaded bung (sump plug) so a grease gun can get to the nipple and pump it each time you do an oil change

It would seem to me to be a solution to a not so real problem - with some potential drawbacks. The lube for the splines really only need to handle a very small axial movement, therefore not so difficult a lubrication problem, more a question of the lube staying where it is needed.

If you add an oil bath, the you will also add some heat generation from splashing the oil around, and have a lower film viscocity than the joint was intended for.

Well, when you've got an idea lurking in the little grey cells you have to do something about it don't you?
I've recently been painting an 'e-bay' bevel box and swing arm to swap the items on the outfit, so it was a good opportunity to make the bits and see what happens.



I made the seal carrier with a flange so that it will be easy to take out for access to the drive shaft without removing the swing arm.

The next problem I found is that the drive shaft is hollow and has an 8mm hole behind the universal joint. After faffing around with various ideas,
I decided to fill the shaft with silicon sealant !!!



The 10mm filler plug incorporates a breather cap and the drain plug is 6mm.



My original guesstimate of the oil volume was way out, there is a nominal 50cc total, so about 30cc will be the starting point.
Now, all that remains for me to do is strip out the swing arm and put my shiny black painted bits in place.
I'll keep you posted with progress as it happens, but if nothing else, if my bike survives, it will confuse some restorer in 50 years time.
Cheers,
Paul.

Good luck with the experiment Paul! If you've got an itch you've just gotta scratch it sometimes!

Best
Dave

I've been doing a some work on the outfit this week, just tidying things up a bit, and after giving the RHS gearbox housing a coat of paint, I thought I might as well put the newly repainted swinging arm and bevel box in (with the oil bath mod). Well, there it is, all assembled and nearly ready to try.



You can see the filler/breather cap just in front of the caliper mounting.

Fitted my new floating rear disc at the same time, so it will be interesting to see how that performs.

Hmm....Must remember to put the back wheel in before I go for a run.

Paul.

Lookin tidy Paul

88

Very interesting. Although some K riders don't see it as a problem, I've had to replace the final drive bearing on mine and I suspect that pulling a sidecar adds a new dimesnion to the whole scenario. A guy who used to race K bike outfits once told me to expect way less life out of the final drive when using a sidecar. What's your experience with this? Since I put in new bearings, I change the final drive oil before virtually every long run. I may be paranoid, but that doesn't mean they're not out to get me. Great work, Paul.
Sean.

Actually, Sean, my 16 tooth final drive splines that I've (temporarily) replaced with a worn 20 set, are perfect, with no sign of wear. It's only been in the last couple of days that I've really looked at them properly and I was quite suprised. When I've painted my original bevel box black I'll be refitting it.

This is the original 1986 spline after 96K miles.


In 1992 I had a universal joint catastrophic failure and bought a new shaft. Thinking that this would be a common problem with an outfit, I bought another brand new shaft as a spare. That seems to be a guarentee that I would never need it! It's still in it's BMW brown paper wrapping.

Apparently, there is a cyclic difference in speed between the input and output of a universally jointed shaft which is magnified as the angle of the shaft is increased. I believe that this causes the spline wear.

On the outfit I have a shortened rear shock and quite hard suspension, so the angle of my drive shaft doesn't move a great deal. A friend followed me on his 1300 Yam outfit last November and said "Does your rear suspension move at all?" Perhaps that's why my splines haven't worn.

I have replaced the big bearing twice though, that gets a raw deal on an outfit.

Paul.

I've got two spare final drives. Am going to put new bearings in them to have them ready for immediate replacement. The time the big bearing went was 400 km from home, but now I think I'll recognise the symptoms well enough, not to head off on that sort of ride!
Good news about the splines.
Sean.

Those final drive were not designed to have that lateral load that a bike with sidecar gives they were only ever designed to take a vertical load which under normal circumstances is all they get.
The bike may lean over but the load is still a vertical load at 90 deg to the axle axis.
They are noted for giving up uhe ghost with a chair attached.

Another thing the guy who raced the outfits told me was that a double sided swingarm is also necessary to reduce this lateral load effect. I think this ties in with Sidecar Paul's shortened rear shock with limited travel. I guess BMW stropped making bikes that were directly suitable for sidecar use when they stopped making those swing arms.
Sean.

I like that you have taken something that is inherently a weak point, partially due to the laziness of owners (lack of maintenance) and partially because BMW coulda done it better, and come up with a potential fix that is ingenious!

I'd like to see how the drive splines fare after several years and a coupla hunnerd thousand kilometres.

Did a test ride today.
Of course you can't feel anything different to a greased spline, but I fitted my clutch arm with the PTFE bearing (see thread 'stubborn clutch arm bearings') while I had the swing arm off and that's made a big difference.......it suprised me. So smooooth.

One problem is my breather cap, after a stretch at 80 mph, it leaked oil, so that's back to the drawing board.

Sean, I don't think the standard swing arm is allowed for use on sidecars in Germany, they have to have double sided steel arms. They gain in some areas, speed limits; but lose out in others, ie build restrictions.
Here's EML's version:-



GITH, yes that's the problem, I can't see me doing enough miles to prove the system. Perhaps I should ride overland to Oz so you guys can inspect it first hand.
Paul.

My recently aquired 1980 R45 runabout has oil lubrication of both the rear hypoid gear and the spline in separate compartments of the rear axle housing.

Paul. I heard a rumour someone is building a bridge to Australia. That will make it easier.

I hope we'll be riding on the left.

I was just having another read of your efforts and it occured to me when I saw the picture that the oil would come out the breather, then of corse I read that it had. my guess is that by now you have added a tube and relocated the breather up near the pivot point on the gearbox, to eliminate that issue????? I would have been more interested in the tailshaft than the final drive in your picture as for me that is where the trouble starts. Anyone agree????

K75cster wrote: my guess is that by now you have added a tube and relocated the breather up near the pivot point on the gearbox, to eliminate that issue?????

My drive system has an oil filled bearing block, driven at engine speed, which always meant taking off the awkwardly placed level plug to check the level. Its now modified by adding a tube to a higher level topped off with a reservoir. This results in no pressure on the seals due to heat build up and the level is confirmed by a glance at the reservoir which can be easily topped up if required.
I did have a problem with the main fan sucking the oil out the vent hole but thats a post for a different forum

A twin sided swing arm a hovercraft and here I am thinking it abit radical to be considering turning the K100 engine into a trike by buying an old auto front wheel drive 850 or 1000cc car front end and using it at the back, amazing this forum dead set amazing

K75cster wrote:A twin sided swing arm a hovercraft and here I am thinking it abit radical to be considering turning the K100 engine into a trike by buying an old auto front wheel drive 850 or 1000cc car front end and using it at the back, amazing this forum dead set amazing

Somebody else with a hovercraft also has one of these, sorry for going off topic.
http://www.grinnallcars.com/scorpion-III-sports-car.html

K75ster,
Yes I'm contemplating a different breather arrangement (but I'm using a solo for this w/e's camping, so there's no panic).
What do you mean by 'tailshaft'? Not a term I am familiar with.

BTW, the double sided swing arm is not my bike, it belongs to a friend who lives in France, hence the chair is on the wrong side.

Thanks, Hover, I like the idea of filling the spline cavity with oil and having a remote reservoir. I'll have a think about that.

Cheers,
Paul

75ster,

Thinking about it, I guess you mean the splines at the tail end of the drive shaft, so here's the picture:-



They still look good.
Cheers,
Paul.

Paul, tailshaft is Aussie English for the driveshaft, usually in relation to rear wheel drive cars.
Have a good weekend and get a few miles into ya!
Sean.

Struth Paul those splines do look clean and bearly marked. As I mentioned in another thread i thought the difference in expansion might explain the wear we have experienced between the F/D and the driveshaft splines, yours have been hauling around more weight than Mine and look new mine stripped maybe I used em to hard down shifts etc

Hi I'm back,
The only reason I can sumise for the splines being so good is that with my shortened shock, the driveshaft is almost horizontal and with limited rear suspension movement the 'tailshaft' (see I'm learning) angle doesn't vary a lot. This means that the variation in the rotational speed of the shaft is minimal and comes back to my original suggestion that the main cause of wear is the hammering effect caused by the speed difference.

Sounds reasonable to me.

BTW K75ster, I've also been towing a trailer for thousands of miles,with a rather heavy model traction engine aboard; sickening, isn't it?

Cheers,
Paul.

Struth if I ever buy a new tailshaft (see i'm consistant) and a new F/D I'm gonna send them over to you to bed in for me. You've stumbled on a secret formula for longevity with splines, You may have to ride all over the place towing the trailer and (muttering to the bride sorry dear but you see I have to do this) doing this task for your fellow K series riders. tough job but someones gotta do it

This treat really triggers the grey cells. I wonder if you could just put a paralever shaft in a standard set-up and thus avoid all issues. The fact that the standard (or old) set-up doesn't have the aft most pivot point should not matter. You could have a similar connection as at the gear box, with a fixing ring, at the FD and let the spline transfer between both joints take up whatever forces are there, over a larger surface, so less wear. You probably could close off that spline and part fill it with grease/oil.
Is there a length difference between an old shaft and the newer paralever shafts?

I made a new breather fitting today.



I routed the tube into the tool tray under the seat......don't laugh, there's madness in my method (yes, I think I've phrased that right)
One, there's no chance of water getting into the hose and, two, if any oil does find it's way up there, it will be easier to clean out the tray than have oil splattered over the back end of the bike.

I'll use the outfit for this coming weekend's camping trip to March in Cambrigdeshire, so we'll see how it goes.

Paul.

Today's daft idea!

How about cutting and welding two tailshafts (I'm getting to like that new word) to make a 2UJ shaft?

Of course you would need a 16 spline FD.

Paul.

Where's my medication?

Well,..... I don't want to be a party pooper on this issue, but I feel the need to clarify a couple of things and maybe also stir some more of those grey cells into action.The uni joint is, by definition a means of transmitting torque through an angled arrangement. The problem is, due to its' design the joint does in fact cause the shaft to speed up and slow down twice per revolution. This has been discussed prior in this thread, and while it is a fact, it may not be the sole, or root cause of the rear spline drive failure. Reason - the shafts on both sides of the uni joint are subjected to the same acceleration/deceleration forces per rev, in this case it is just the front yoke which is the "other" half shaft. So the question is: Why doesn't the front spline connection (gearbox output shaft) give trouble ? My reasoning is that it is a fifferent fit, the uni yoke (female part) is of cast or forged steel and it is not required to slide in service. But make no mistake about it, the yoke is still subjected to the same forces during rotation as the rear spline assembly. I believe the oil is an excellent solution, though is is cerainly a challenge to seal, keep in there etc. I'd like to see someone build a complete drive shaft without the rubber damper, and modify the inside of the swing are tube to accomodate a seal and slinger ring arrangement to keep the oil where it's required. Thinking caps on,......

Ignore post 34.

For it to work the splines at both ends would need to remain parallel.....umm, PARAlever.

Paul.

(couldn't figure out how to delete it)

Dennis wrote:... Why doesn't the front spline connection (gearbox output shaft) give trouble ? My reasoning is that it is a fifferent fit, the uni yoke (female part) is of cast or forged steel and it is not required to slide in service....

Hi Dennis, I think that the answer to your question is that the shaft between the ujoint and the gearbox's spline has a rubber damper, this absorbes most of the torsional speed variations and deformations, relieving the gearbox spline from the associated stresses.

The FD´s side spline has to deal with both the torsional speed variations and the axial displacements. Being the more solicited and not the strongest part of the system, is the first to yield.

Best regards
JAP

Going to March, Sidecar Paul, I'm spitting distance from there. John

Hi John, Call in and say hello.

Scout camp, Gaul Rd. There should be several K outfits, and maybe some K solos.

Cheers,
Paul.

There's nothing wrong with post 34 that a rotary bur wont help. oh and an angle grinder and a welder and some thead tape

will do, paul. John

Oh dear, "the best laid schemes o'mice and men"

After the first 300 miles or so, I checked the oil by draining it, only a few drops came out.
I re-filled the complete cavity and some 400 miles later about 5cc came out.

Today I pulled it apart and found that the oil was migrating into the swing arm. I guess that because the shaft is a loose fit on its spline (it was a s/h bevel box and shaft), it's rotating slightly eccentrically under load and the oilseal has not been able to cope.

I've now re-fitted my original 16 tooth rear drive and shaft, with grease lubrication and I think that a more elaborate seal will be required before I try again.

An interesting point is that the witness mark on the shaft from the oilseal showed no lateral movement.

Ah well, back to the drawing board!

Paul.

Paul I believe it was slartibartfast who reminded us that it was quote"The best laid plans of mice" Apparently we were left out of it. So no lateral movement at all? The witness mark was no wider than the seal contact patch? All in perfect contrast. Maybe we need the splines made from similar tonnage steel (what ever tonnage that is on the F/D) then we should get equaler milage from both. Not that that should worry you, yours look perfect. The trailers for boats use a grease filled void under spring pressure to keep them working for long periods whilst being ignored by their owners, maybe there is something there for thought. regards Keith

sidecar paul wrote: Ah well, back to the drawing board!

Paul.

The little one or the real one?

Here's the picture Keith.



Paul.

Hi all,

I’ve contemplated the spline issue for a bit now and come to a conclusion that the problem is twofold. Yes, we need to lubricate and keep it serviced, but the problem is primarily the design and out riding techniques/conditions.

Let’s not go to design because nothing can be gained there, suffice to say that my 1976 Goldwing and CX500 Honda shaft drives are not plagued with the problem. I am on thin ice here because I don’t really have much experience with other makes.

Let me look at the 1986 and earlier bikes, the bikes with Jetronic engine management.

The clank in the drive we get when we decelerate and accelerate is what destroys the splines. Slight movement back and forward along the splines is of secondary importance, I believe.

So minimising that clank is the key. People who ride/cruise/tour without using the gearbox much may not have any problems with the shaft drive, but people like us who ride in suburban setting with lots of corners, intersections, roundabouts, traffic need to use the box a lot. Each change and deceleration needs to be smooth and without that clank to minimise the problem.

My solution was to initially disconnect the TBS (TPS) which caused a lot of low speed jerking on the shaft due to electronics switching off and on of injectors. It transformed my bike from a beast that was annoying to ride to a very smooth bike almost like my K1200.

If that works for you, it was simple to reconnect the TPS and “tune out” the switch off function and leave the full throttle micro switch functional. To be truthful the TPS on these bikes must have been there to stop slight backfire and maybe as an early attempt for pollution control. I think that it was a very crude system.

This will only work for bikes before Motronic electronic system, ie very early K100s up to 1987(88?). The computerised system is different and CAN NOT BE DISCONNECTED.

The L-Jetronic system was used on all the 8v bikes right up to them being discontinued in 1992 but was not used on the 16v engines from inception in 1988. They all used the Motronic 2.1 for early and 2.2 for the later units and all the 16v bikes also had the paralever rear drive which isn't prone to these problems.
I can see where you are comming from and agree that the problem is more pronounced on bikes that do city and commuting rather than long distance touring.
The other factor is that the early K100s with 16 spline drives wern't anywhere near as prone to the problems.
From my experience in drive shaft technology the problem lies in the hammering the speed differences between the two parts of the uni joint causes and not having the right grease.
Whereas the paralever drive has 2 uni joints which if phased correctly will eliminate that hammering.
My Z1300 Kawasaki has a similar setup with one very distinct difference and that is instead of a internal/external spline at the rear of the shaft it has a coupler which is a similar style but 3 times the diameter of the splines and so reduces the hammering by a factor of 3 and increases the load area on the splines by a factor of 4 (deeper splines) so that is a reduction of more than 90% of the hammering effect. I have in 279,000Ks never had a problem or had to service the coupler and only twice greased it and that was only when I had it apart for other work and renewed the grease.
From my days in drag racing (bikes and cars) a single uni joint was an expensive disaster waiting to happen regardless of the size of the uni but a coupler which was barely half as big again as the one on my Kawasaki would not break even under the stress a 2000hp blown top alcohol engine would exert on it.

Rick G wrote:The L-Jetronic system was used on all the 8v bikes right up to them being discontinued in 1992 but was not used on the 16v engines from inception in 1988. They all used the Motronic 2.1 for early and 2.2 for the later units and all the 16v bikes also had the paralever rear drive which isn't prone to these problems.
I can see where you are comming from and agree that the problem is more pronounced on bikes that do city and commuting rather than long distance touring.

....The other factor is that the early K100s with 16 spline drives wern't anywhere near as prone to the problems.
From my experience in drive shaft technology the problem lies in the hammering the speed differences between the two parts of the uni joint causes and not having the right grease.
...
....barely half as big again as the one on my Kawasaki would not break even under the stress a 2000hp blown top alcohol engine would exert on it.

Hi Rick,

Thank you for clarifying the Motronic/Jetronic dates, I simply forgot the years.

I've posted before on the TPS problem and I can assure the people that disconnecting the thing to try does nor harm no does it increase/decrease the fuel consumption. It is perfectly safe to try; the results may surprise you . It is a one minute job.

It is the design problem. I was converted to shaft drives because of superb CX500 set-up. Even the 1976GW is great. From memory the Honda setup has a loaded spring coupling. I must say that K100 was a little disappointing in that area because it all looked a little agricultural (sorry, but not all things BMW are great:) ).

My band-aid solution is just that, a band-aid but it has an added advantage that it makes the bike very nice to ride when it comes to technical riding, i.e. twisties and slow tight corners and traffic.

Yeah it's a design problem all the way and how BMW managed such a monumental cock up is amazing when many of the Japaneese bikes before them were quite good and apparently did their homework.
And thinking back on it the 16 spline units can't have been that good or why did they change.

And as for the TPS just feed it to the dumpster they'll eat anything, although not having the full throttle rich could cause problems with sustained high speed work which was where the L-Jetronic was at it's worst and does lean out.

Rick G wrote:Yeah it's a design problem all the way and how BMW managed such a monumental cock up is amazing when many of the Japaneese bikes before them were quite good and apparently did their homework.
And thinking back on it the 16 spline units can't have been that good or why did they change.

And as for the TPS just feed it to the dumpster they'll eat anything, although not having the full throttle rich could cause problems with sustained high speed work which was where the L-Jetronic was at it's worst and does lean out.

Yep, CX500 production stopped in 1983. Shaft drive was a superb, most precise bit of engineering ... I just loved it.

I left it on the bike but "tuned" it out. Simply adjust the throttle off position never to activate the micro-switch. Done by simply rotating the TPS until the "off" position micro-switch never activates. That way you can keep your full throttle function.

BTW for people who are not familiar with this... The TPS contains two micro switches, one for full throttle to inject about 10% more fuel into the engine (enrich function) and the other is the "throttle off" position that shuts off power to injectors. This one causes problems because it is a simple on/off thing. Effectively it stops/starts the engine thus inducing the twisting forces onto the spline each time in both directions. A pest in my opinion that has very little practical value.