FD/Driveshaft Spline rebuild options in 2024

[JanekW]

I'm currently working on someone else's abandoned project '89 K100RS, and was saddened to see the state of my driveshaft and FD splines.

After some digging, it seems that getting FD/Shaft splines rebuilt is quite difficult in 2024, especially for us Canadians.

My understanding of the FD/shaft spline rebuild situation in 2024:

• Hansen's in OR burnt down in 2020. I see no updates on any social media, and their website is down - I assume they haven't rebuilt yet and are not open for business.
  
• Bruno's in Canada is out of business since 2017 or 2018.
• K Parts Holland has rebuilt driveshafts available, but no FD splines/rebuild service
• The state of ebay final drives is far from good. Many sellers are deliberately avoiding close-up pictures of splines, and others are severely rusted or in otherwise poor visual state.
• Beemershop.com offers a rebuildable driveshaft here:https://www.beemershop.com/product/ei-k75k100-driveshaft-20-tooth.html, but also no FD splines or rebuild service as far as I can see.

While a couple of options remain for the driveshafts, it seems we may be running out of options for final drives: either find new parts from BMW or chance a used final drive on ebay. I'm hoping someone knows of another option that I may not be aware of?

I'll take the shaft and final drive to a few driveline places in town, maybe someone would be willing to weld on new splines. I'll report back if any driveline/machine shops here in Calgary, AB are willing to work on BMW final drives.

State of my splines:




Let me know what you guys think!

[milq]

Both  Kparts and Motobins (UK I think) offer the replacement splines for the driveshaft, as you likely already know. Around $88 USD plus shipping isn't bad if you have someone who can reliably do the repair for a reasonable price.

The following is from the BMWMOA forums in 2018:

"Bombers Beemers in Durham, NC (Bombars is correct spelling)
They offer a full rebuild of the final drive with new pinion shaft spline, new drive shaft, clean and reseal. ($989.95 with 1yr/12k warranty - it is noted that the metal in the new drive shaft splines are supposedly better quality than original)"
ME: Heck of a deal for a new shaft and a FD rebuild...if it's still available.

Edit:  I just looked up Bombars Beemers and the website says they are in Wilmington NC and "spline repair" is listed  under machine shop services.

https://www.bombarsbeemers.com/copy-of-head-rebuilding


To my knowledge the Final drive spline repair is full replacement of the pinion gear with a new BMW part, apparently there are several special tools required to disassemble and reassemble the FD properly...but I don't  have first hand knowledge of that. Setting up ring and pinion in cars/trucks is pretty easy though, worth noting that both (automotive) ring and pinion are replaced as a set typically, not sure if that's required here. If I could get hands on the FD tools and procedures I'd offer the service myself. I have a full machine shop at my fingertips and 30 years of machining and industrial maintenance under my belt but no specific experience with manufacturing new splines so can't offer to make the actual parts myself.

[Laitch]

. . . worth noting that both (automotive) ring and pinion are replaced as a set typically, not sure if that's required here. If I could get hands on the FD tools and procedures I'd offer the service myself. . .

The crown gear and pinion are only sold as a set, hence this guidance from BMW's K100/K75 2V shop manual.

[JanekW]

Thanks for brining my attention to Bombers Beemers. I went through their site earlier but couldn't find anything about FD rebuilds, so I appreciate you linking me.  1330 Canadian Pesos is not bad at all considering a driveshaft is included, as well as the peace of mind that the FD will be like-new and likely outlast the rest of the bike with proper spline lubrication. I'll shoot them an email and ask whether or not the price is still accurate in 2024.

I also took a closer look at kpartsholland, and they offer a refurbished driveshaft for 230 usd +shipping. A steal of a deal, and probably cheaper than buying the stub + finding a local machine shop to do the work, makes for a really good alternative if Bombers doesn't work out. https://kpartsholland.com/products/rebuilt-driveshaft-20t-26111454063

I spoked with my local BMW today and according to their computers, BMW is no longer producing the crown and pinion gear, and you're correct about them being sold as a matched pair. They pointed me towards looking for a local machine shop that might take the project on, or buying a used low-mileage final drive.

Also found a couple of potential used FD candidates on ebay for cheap, but I'll have to ask the sellers for up-close pictures of the splines before I consider it.

[milq]

I'll shoot them an email and ask whether or not the price is still accurate in 2024.
 

If you scroll down the page far enough they do show pricing for the rebuild at roughly that same price.

 

BMW is no longer producing the crown and pinion gear

THAT is a big problem for the future, I guess we knew it had to end at some point. Maybe we'll learn that Bombars bought out 10,000 of them! Or have a procedure to repair the  existing splines on the pinion  shaft...I'm certain that's possible I've just never done it. 
 

Also found a couple of potential used FD candidates on ebay for cheap, but I'll have to ask the sellers for up-close pictures of the splines before I consider it.

I did that when I bought my K75, even though its FD and splines seem ok and are relatively low mileage (34k). The unit I bought is in pretty good shape but isn't perfect either.

[frankenduck]

Note: Most Ebay sellers have free returns where they pay return shipping.

It's not great for sellers but if there's a dispute over an item then Ebay almost always sides with the buyer.

I bought an Audiovox cruise control on Ebay a few years ago. The scumbag seller shipped me an empty box so there would be tracking and it looked like I actually got something. Ebay sided with me and I got a full refund.

[JanekW]

It's not great for sellers but if there's a dispute over an item then Ebay almost always sides with the buyer.

That's fairly reassuring, but I would imagine that when it comes to a used final drive that's being sold "as is" you might have trouble pursuing a refund. Many of the ads have numerous pictures which may, to a layman, come across as detailed even if they're hiding damage to the input splines.

Regardless, it remains as the cheapest alternative. I'll wait and see what extra photos I can squeeze out of the sellers before I commit myself to a more expensive full rebuild.

With the gears being out of production, it may be wise to pick up a FD for the gearing, even if the splines are kaput.

[Laitch]

With the gears being out of production  . . .

I buy parts from the MaxBMW branch in N. Hampton, New Hampshire although they aren't often needed.     When looking at the parts list in their fiche, NA at the end of a part's description line means the part is Not Available. If there's a price at the end of a description line, its presence can mean the part could possibly be obtained from inventory, either in the branch being searched or from another branch. It could also mean that it can be shipped from overseas.

Right now in MaxBMW's fiche, RS pinion and crown gear sets are listed as NA but RT 32:11 sets for 2/86 models onward are price listed. You should be able to substitute one for the other. If hunting for a decent used drive goes cold, those sets—plus suitable shims, bearings and seals if needed—could be an option although there will be a change in the performance curve.

If you find an attractive used unit, please share the photos here; however, good splines should be obvious.

Good luck!

[frankenduck]

Another option is to look at used stuff from an 85 K100. Those have 16 splines at the shaft/final drive junction and don't wear like the 20 spline setup. Being early, the FD only comes in silver and not black.

[JanekW]

Received this picture of the splines from a seller letting a 32/11 FD off of an 86' RT with 60K go for super cheap. They look good to me - thoughts? Going from 2.81 to 2.91 will bump my RPM somewhat on the highway, but besides burning a bit more fuel and being more noisy, I don't really see any other downsides.



Pairing this with a rebuilt shaft from kparts gets me on the road for about 500CAD - not bad at all.

[frankenduck]

The majority of the wear occurs on the shaft splines so you should be fine with a 60K FD.

RPMs will go up 3.2% but you also get a whopping 3.2% more torque at the rear wheel.

[JanekW]

Ended up purchasing the used final drive I posted earlier, along with a new (rebuilt) shaft from kpartsholland. All-in cost post shipping is roughly $500CAD, so not bad at all assuming nothing is wrong with the FD. Ill post a couple detailed pictures of the rebuilt shaft, and comment on how the new splines fit the used drive when all of the parts come in. Thanks for all of the advice.

[Arktasian]

Are you aware of  - stuffing/ fashioning a plug into the shaft to keep lube trapped back at the splines where it needs to be (rather than migrating forward)

[frankenduck]

Are you aware of  - stuffing/ fashioning a plug into the shaft to keep lube trapped back at the splines where it needs to be (rather than migrating forward)

Have you ever noticed which way the drives shaft is tilted? Do you think material tends to migrate with gravity or against gravity?

[Laitch]

Have you ever noticed which way the drives shaft is tilted? Do you think material tends to migrate with gravity or against gravity?

I haven't noticed the driveshaft's tilt when a rider is mounted but it could likely be parallel to the pavement—depending upon the tire aspect ratio, the shock absorber's spring rate and how rebound and compression of the shock is tuned—when the Brick is supporting a rider of 180lbs, and if that is the case then the rear of the shaft is tilted upward during moments of deflection from bumps in the road. Of course, whichever direction the shaft is tilted is of no concern if the rear drive's shaft hasn't been lathered up barber-style with moly paste. 
I have observed cookie batter climbing up a kitchen mixer's beater shaft while the beater is facing directly downward but the batter didn't contain molybdenum so that could be an unfair comparison. 

[Arktasian]

Sorry, not intending on re-initiating a consideration of spline lube tech and pitfalls. Off riding season (for many) does tend to afford some extra time with which to debate pretty much anything.
I suspect the kitchen mixer comparison isn't that unfair an observation with batter climbing upwards on spinning blades, much like the centrifugal force created by rotating something easily overcomes gravitational forces (satellites, rockets, flying monkeys with jet packs etc.)
To me, closing off any extra spaces that desired lubricant "might" gravitate (or shall we say anti gravitate) towards especially when it involves something as simple as a plug with a touch of perimeter sealant, seems pretty harmless.

[JanekW]

To me, closing off any extra spaces that desired lubricant "might" gravitate (or shall we say anti gravitate) towards especially when it involves something as simple as a plug with a touch of perimeter sealant, seems pretty harmless.

I agree with this, although I'll admit that I am fairly inexperienced with K-bikes.

Even though the driveshaft is angled down towards the FD, I would imagine that the relative movement of the driveshaft/FD splines is the primary driver of the migration of grease, rather than gravity effects. I say that because spline grease is typically very thick, even at operating temperature. 

In my mind, this would mean that the spread of grease over time would be roughly equal in both directions, with perhaps a 'slight' bias towards the FD due to what (if any) gravity effects may exist.

I might give this technique a try, and report back with pictures of the splines after 5K km.

That or we see if we can convince SpaceX to send a K-bike to space, where we can perform this experiment in zero G.