K75c drive shaft replacement

[Mishb93]

Greetings all, long time lurker, first time poster here.


I bought a '85 K75c with 62000km on the clock. I've put 10k on it since. I recently took off the final drive to lube the splines and found them worn to knife edges.
I live in South Africa and used parts are like hen's teeth here. A new drive shaft from BMW costs more than I earn in a month, that is about a quarter of what I paid for the bike, so I'm hesitant to go that route.
I've considered the possibility of taking the drive shaft and the final drive to an engineering shop and asking them to fabricate something for me, or perhaps recondition them. Has anyone experience with such a thing? Is this recommended against for some reason?


Worst case scenario, if I have to buy a drive shaft from BMW, how bad of an idea is it to use it with the old pinion? The wear on the pinion doesn't look too bad, and there seems to be some disagreement about this on the forums.


I love the bike, and I've no reason to believe there's anything else wrong with it, so I'd like to keep it on the road.


Any help will be greatly appreciated

[Motorhobo]

Worst case scenario, if I have to buy a drive shaft from BMW, how bad of an idea is it to use it with the old pinion? The wear on the pinion doesn't look too bad, and there seems to be some disagreement about this on the forums.

I love the bike, and I've no reason to believe there's anything else wrong with it, so I'd like to keep it on the road.

You'd be smart not to put the FD back on with those splines -- someday soon you're going to give throttle and have 0 power, and that's a very dangerous situation. Go here today:

http://kbikeparts.com/

and get Drake to send you one of the driveshafts he's got on his site -- search the page for 'drive shaft' -- he spells it there as two words. He's got three available when I just checked, assuming the ones he's got will work with your K75C. Ask him -- he knows. As to whether the DS and FD should be a match, or whether you should put a new DS on a FD with worn splines, isn't that point moot? In an ideal world, everything would be ideal but it's not and you have a 30 year old bike. If it were me, I'd get a decent looking drive shaft from Drake, lube the splines properly, and stick it in there and proceed to motobricking for the next 6k miles, then lube again and repeat until the thing dies. The world will probably end before you need another driveshaft or FD splines.

I bought a new DS from BMW for $350+ bucks -- in retrospect I probably should have gotten one from Drake and followed my own good advice. He ships internationally on orders over $40, according to his site.

[Filmcamera]

If Drake cant help you let me know.  I just purchased a new transmission for my bike and it came with a driveshaft.  It arrives this week so I am not sure what the splines are like but I can ship it to you if needed.


Do the research though, it is from a 1993 K1100 RS so I am not sure if it fits.

[Dennis de Vries]

Film that's a great offer but it will not fit the OP's bikes. A K75 has a monolever, a K1100 paralever. Would need more than just a DS to make that work...

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[Mishb93]

Thanks for the replies. I appreciate the offer, Film.
I may be missing something, but when I search kbikeparts.com I find one block advertising a K75 DS and final drive, but it says it's sold.
Is there a fairly quick turnover of these parts? Is it a good bet to just keep my eye on the site for a new DS to pop up?

[Motorhobo]

I see 2 Z20 drive shafts and 1 Z16. Search for 'drive shaft' or Z20 or Z16...

They were there 2 minutes ago.

[The Mighty Gryphon]

Some options to investigate:

There is an aftermarket BMW parts place in the U.K. (Motobins?) that has a repair spline for the end of the drive shaft.  You take the part to an engineering firm and the cut of the old spline and weld on the new. 

Price as I recall is something less than $100US. 

There is also a firm in Japan that makes replacement drive shafts.  I believe Mlytle has one of their drive shafts on his K75.  It has a longer spline section and the u-joint is repairable and has a grease fitting so it can be lubed.

[K1300S]

yup.  highly recommend the IE driveshafts from ted's beemershop.  he is just one of the retailers for IE stuff. 

i would caution though...if the FD end of the DS is that bad, then the FD input splines are near as bad.  you put a new DS on crappy FD splines and the new DS will quickly be trashed.  I know.  i did it.  in only about 200 miles, it was already evident that the DS was getting chewed up.

it sucks, but that is the nature of these bikes.  we don't have cheap chains.  it costs a lot of money to fix FD splines and DS's.

[Motorhobo]

https://www.james-sherlock.co.uk

I just checked out the above link under 'Swinging Arms and Driveshafts' -- ain't nuthin' there!


Anyway, the operative phrase for this issue is 'How much money do you have today'? I just checked out the two final drives I have lying around that ran paired with worn driveshaft splines, and sure, they have wear that would probably transfer to any driveshaft they're paired with. But if you have $100, you get what you can, accept that it's a temporary solution, lube the shit out of it and commence to motobricking as long as you can. That philosophy worked for me for over 20k miles. When I got a little money I replaced both worn parts with new or new-condition.


My point being -- $100 gets you a lot of motobricking whilst you save for the Big Fix.

[Mishb93]

Motorhobo: my apologies, I didn't realize Z20 and Z16 fitted a K75. I count 20 teeth on mine, that makes it a Z20?


Thanks for the info all, most kind, much obliged.


Working with a quickly wearing DS on my old final drive might have to be the answer. I'm pretty happy to pull off the final drive every other week to lube it up if that's what it takes to stay on the road.


The Jap DS from Ted's Beermer Shop is more costly than the one from BMW.
Moto-bins has a weld-on replacement spline for around $90. Engineer shop charge? Who knows. Seems like a sweet option to me.
Kbikeparts.com has the two shafts with fairly worn splines for $80 and $90.


How is the toothed part of the DS removed? The parts diagrams I've seen have shown them as one piece. Would it need to be cut off to weld a replacement on?


If one was to do the Big Fix, would it be best to replace the whole final drive? I've not seen replacement pinions anywhere, and my Haynes manual says dismantling the final drive is a no go.

[Motorhobo]

I'm running now with a FD with good splines I got off eBay for $200 and change in one K75 and a rebuilt FD and DS I got when I bought a high-mileage runner in 2015 for parts (I ended up parting out a different bike and now am riding that high-mileage runner with the other one's engine). I have three other FDs lying around in various states of wear. I also have 3 driveshafts lying around that are somewhere between what Drake's selling and what you've got. I bought my first spare back in 2009 and didn't have cause to use it until 2013...so you kind of have to plan ahead.

Basically, if you're going to do the cheap and dirty way, just keep your eyes out for used final drives and snatch one up when it becomes available and run with what you have till you find something better. Check with bike breakers in your country. Like I said, it ain't the ideal case but a FD rebuild will cost min $600 and now you know what new DSs cost...welcome to the wonderful world of motobricks.

Seriously, I think you'd be surprised how long a moderately worn FD and DS will last if you keep them lubed. Many thousands of miles.

[Laitch]

greetings...
pick up the tele and call... they gotts stuff that aints on the site... as all bike breakers do...
https://www.james-sherlock.co.uk

I just checked out the above link under 'Swinging Arms and Driveshafts' -- ain't nuthin' there!

I think j o's point is that Mishb93 should call Sherlock because they might have one that isn't listed—the presumption being that Mishb93 would use the link to obtain Sherlock's phone number. Sometimes parts are being received but the update of the website is behind in reflecting that.

[Motorhobo]

Motorhobo: my apologies, I didn't realize Z20 and Z16 fitted a K75. I count 20 teeth on mine, that makes it a Z20?

Guess so, -- check with Drake about your specific model and year.

If one was to do the Big Fix, would it be best to replace the whole final drive? I've not seen replacement pinions anywhere, and my Haynes manual says dismantling the final drive is a no go.

Getting new gears from BMW is much more expensive than getting a used FD and comes close to the cost of a rebuild by an experienced BMW mechanic. Maybe you should be looking for a parts bike :-)

[Motorhobo]

I think j o's point is that Mishb93 should call Sherlock because they might have one that isn't listed—the presumption being that Mishb93 would use the link to obtain Sherlock's phone number. Sometimes parts are being received but the update of the website is behind in reflecting that.

Missed that.

[The Mighty Gryphon]

There is an outfit in California called Safari Cycle that at any point in time has at least 4 or 5 brick engines for sale on eBay.  I never see them selling a DS.  Might be worth contacting them.

[Motorhobo]

How is the toothed part of the DS removed? The parts diagrams I've seen have shown them as one piece. Would it need to be cut off to weld a replacement on?

BTW about this -- if driveshaft splines are really bad then the condition of the u-joint might also be in question. Welding on a new spline piece does nothing to address that. So you might get new splines but the u-joint could fail next week. IMO a used driveshaft with decent splines and a good u-joint is a better option -- at least you know it has either been well maintained or has relatively low mileage, and neither of these could be true if you try to salvage an old DS by replacing the spline head.

[Mishb93]

Hi all, thanks to the kind help of those who posted on here I got and fitted a good used drive shaft, from Drake. While I was at it I decided to pull of the swing arm and grease the splines up there. The rubber gaiter which seals off the drive shaft between the gear box and the swing arm was cracked, and hadn't been seated in the swing arm. As far as I understood from my Haynes manual I was to push the swing arm against that seal so it pops into place, then attach the swing arm. I couldn't get it to stay seated, it'd just pull out again. I don't know if there was some part missing, I just wasn't doing it correctly, or the gaiter was just finished.
My question is, how important is that gaiter? I saw no signs of much dust or any water getting into the swing arm. Is it best to try and get my hands on one (tricky in my country), or should the bike be okay without one?

[Filmcamera]

I had a similar issue, when I took my swing arm off the boot wasn't connected at the transmission end.

You have the method of installing it the wrong way round.  The boot is connected to the swing arm first and held in place by a snap ring.  Then you push it into place on the gearbox end. 

It might take a few tries for it so seat correctly but if it is badly seated you will know because it will be hard to get the pivot pins installed.  It took me a couple of tires but eventually it seated great.  It is better to have it installed if possible.  Running without is going to allow dirt etc get into the swing arm and is bound to increase wear on the driveshaft.

[Motorhobo]

I got a fully intact used swingarm boot off US eBay for $10 with shipping -- came with the snap ring. I think Filmcamera is right -- you can run the bike without it but it's advisable to get one, clean up and re-lube the driveshaft/trans splines at the output shaft end and install the boot and snap ring as soon as you get a chance.

[Al]

Does Bruno's in Ontario still do spline fixes? I haven't heard anything about him in recent years. Seems it would be a good business to be in if one was experienced and had the machine tools already. One would need to be able to cut splines so an old shaper would likely be required.


Bruno's also put a plug in the DS splines so grease would not be forced up the drive shaft and away from the FD splines. Not sure how this was done.  My bike was so modified by the PO. Bruno's also had an extended FD spline so that there was more surface area on the splines to take the load. My bike was not so modified : (


So far no wear that I can detect. I use the Guard Dog Moly lube.