Rear Splines Worn - What are My Options?

[julian5000]

Hello Everyone

I've just bought a 1988 K75c. I got it for a good price but bought it unseen, flew half way down the country (New Zealand's not that big), and rode it home. It went well, but I did hit a few false neutrals and I had to blip the throttle changing down to get a smooth gear change.

When I got it home and inspected the rear splines I found this:



I'm going to keep going and inspect the clutch splines too (as well as doing a full service), hopefully I don't find too many more gremlins lurking.

I've found lots of information on preventing worn splines, but not so much on what to do to fix them. I don't have a lot of money to spend (new kid, wife, new business, blah blah!  :musicboohoo:), so I was considering getting an exhange drive shaft from here:

http://www.motobins.co.uk/displayfinal.php?s=0&function=show&subs=073b&title=K+20+SPLINE+DRIVESHAFT+EXCHANGE+SERVICE&model=.

They seem a lot cheaper than any other solution I've found, hopefully that doesn't mean I'll regret it?

So, short story long, I have a couple of questions hopefully someone here can help me with.

1/ Do you think I can ride my bike with the splines in that state while I wait for the replacement to arrive? They're pretty in pretty bad shape, right?

2/ Can I just replace the driveshaft, or do I have to replace the final drive too. This is the other end:




Thanks for any help, appreciate it! I'm hoping I can get the bike into tip-top shape - I'm surprised by how much fun it is to ride. I reckon I could keep this bike for a long time.

Cheers
Julian

[johnny]

greetings julian5000...

welcome to motobrick.com...

if it were me i would score some proper moly... massage it onto and into all splines... put it back together and ride and ride and ride...

pull it apart every 10,000 miles and repeat the moly massage...

unless you are burning out or wheeling that motobrick i betts you will be fine... in the mean time you can start looking used parts in your leisure... then swap them out on down the road if you wish...

moly and spline lube link...

j o

[julian5000]

Thanks Johnny - you just became my favourite forum-friend. I've got some moly on the way and I might just do exactly that. So they're not bad enough to lose any sleep over?  Awesome :2thumbup:

[johnny]

some folks would not ride on those splines... im an optimist... i believe in riding it till it wont move... no worries... no regrets... id go getts yourbaddself some yeeehaaaaa and leave the over cerebralization to the posers...

j o 

[cy7878]

While I would agree with Johnny.  If it's already worn might as well keep riding it.  I would still be on the look out on places like ebay for classified ads to score a set of final drive and drive shaft, both actually come up very often and most of the time in great shape.

You will have to replace both, one worn gear will wear out another because the mating surface is uneven.

[healthy]

I have similar looking shaft splines. I'm going to keep riding on it, though only locally. If it shears i'm never far from city bus lines.

I have plans to do longer rides, so I have gone ahead and picked up a replacement shaft already. when I do those rides i'm going to be carrying a few extra pounds in case it decides to chew itself up at some point. best case scenario, I ride for miles and years on this current one and never get around to using the new one. Bike is at 138k and an '86 with rear drum brakes, If i ever decide to upgrade to a newer/less-used K I have a new drive shaft for that one.

[cy7878]

Hi Healthy,

   If you already have replacements, why not just install them?  The problem with riding on worned shaft is poss vibration.  It's probably no big deal, but if you already scored a replacement set and know how to properly take care of them, why not just...

[detbmw]

I had a very similar issue with my K75S that I bought last September. I sent my drive shaft and final drive to Canada to Burno. It cost me about $800, not counting shipping, for the repairs. I was able to send mine through the US Postal Service. It took almost three months.

I have no idea how you would ship it or how much it would cost, but the end result is a better-than-new drive train.

[pallum]

Bruno's is pricey, but was worth it to me.
Shaft before: http://i.imgur.com/kPvpy.jpg
Shaft after: http://i.imgur.com/Jv1IE.jpg
FD before: http://i.imgur.com/iwEFG.jpg
FD after: http://i.imgur.com/IV9wH.jpg

I'm on the same page as Healthy in this situation. The K-bikes aren't yet "vintage," but there's certainly not many of them around any more. As the years pass used parts will be harder to come by, especially hard wearing parts like our drive train shafts (transmission and final drive). Years from now I wouldn't be surprised to see drive shafts and final drive units a rarity with as fast as we're burning them up so we may as well get as much as we can out of what we have now. It's nice to go over to maxBMW or BeemerBoneyard and pick out almost any part you need, but if you've ever tried working on an early 70's Honda and see the "NLA" label on most of the parts in the site inventory over at BikeBandit or what have you-- you are glad that BMW still provides even the simplest screws. Besides, the cost of repairing/replacing a totally busted driveshaft/FD is going to be the same as for one that's still rideable, and the timing all comes down to rider opinion and wallet.

Not saying BMW will stop supporting the classic K's any time soon, but it's something I appreciate from them and try to "help" with.

JMHO

[julian5000]

Thanks heaps for the input. At least I know my options now. I'm about to pull the gear box off to check the clutch splines, hopefully they just need a good lube.

Cheers
Julian

[detbmw]

Bruno also extends the length of the splines by about 30%, uses a harder metal, and adds a grease reservoir into the drive shaft.

[motodude]

1) IMO you can keep riding it for now.  Lube them up before you put it back together though.  Lots of things are better with lube.
2) From what I can see, your final drive splines look okay.  Just replace the drive shaft and you should be good.

Tom

[healthy]

Cy7878, Replacing them is an option, but i just re-lubed the splines late last year, i'll consider swapping the new guy in when i open things up for a rear seal replacement which is one my to-do list.

As long as i am not getting any back downshifting issues (or if they don't just shear off) I'm in no rush. Just glad i have the replacement part that i can take with me to avoid being stranded somewhere far from home.