Hi all. I purchased a 1991 K100LT a few years ago and it's been sitting for a while. I decided to finally go through it completely. When checking the driveshaft splines I noticed they are completely worn out, real bad... along with the finalshaft splines. There were also rubber bits (look brownish) in the swingarm.

I found a good deal on 1986 driveshaft and complete finaldrive unit; only 7k on them and can see that the splines are in excellent condition. I was wondering if I can just swap these parts out. Does it matter that the 1986 doesn't have ABS? I don't mind losing the ABS. If I can transfer the ABS over from my unit to the replacement unit then I'll do that. 

Also, any idea which seal the brown pieces are from? I'm thinking the whole swingarm will need to be removed... this doesn't seem too complicated.

Any help is appreciated!!

This is how we're looking after removing the swingarm.

Here is the that area cleaned up. This seal looks fine. Are the brown bits from the finaldrive seal? or?

The transmission output shaft splines in your third and fouth post are designed differently than those on the driveshaft rear socket and rear drive. They are clipped to the u-joint coupling splines so are not subject to the sliding wear that has affected the driveshaft and rear drive pinion gear shaft. You could swap the new shaft and rear drive for the old without being concerned about ABS.

An inspection of the transmission input shaft spines and the clutch disc hub splines should be undertaken. Are you in that far?

Where did you find the rubber-looking bits? Moose scat can be ruled out because, generally, it’s spherical.

I haven't gotten to clutch disc hub yet.

The rubber bits were scattered throughout the swingarm... bits were at the driveshaft end as well as toward the transmission end. There was also oil puddled within the swingarm.

Laitch wrote:The transmission output shaft splines in your third and fouth post are designed differently than those on the driveshaft rear socket and rear drive. They are clipped to the u-joint coupling splines so are not subject to the sliding wear that has affected the driveshaft and rear drive pinion gear shaft. You could swap the new shaft and rear drive for the old without being concerned about ABS.

An inspection of the transmission input shaft spines and the clutch disc hub splines should be undertaken. Are you in that far?

Where did you find the rubber-looking bits? Moose scat can be ruled out because, generally, it’s spherical.

Also do I need to worry about the ~1" gap that will be reduced when I use the replacement rear drive? The allen heads are stripped on my current drive from PO... would be nice if I didn't have to worry about swapping the rotor and abs gear.

Here's what I purchased... 

finaldrive: https://www.ebay.com/itm/226410131078

drive shaft: https://www.ebay.com/itm/226410124804

757Brick wrote:
Also do I need to worry about the ~1" gap that will be reduced when I use the replacement rear drive? The allen heads are stripped on my current drive from PO... would be nice if I didn't have to worry about swapping the rotor and abs gear.

Illustrate the "1" gap" and the "stripped heads." The parts you have purchased seem ok. You seemed determined to worry.

Laitch wrote:

757Brick wrote:
Also do I need to worry about the ~1" gap that will be reduced when I use the replacement rear drive? The allen heads are stripped on my current drive from PO... would be nice if I didn't have to worry about swapping the rotor and abs gear.

Illustrate the "1" gap" and the "stripped heads." The parts you have purchased seem ok. You seemed determined to worry.

The ABS gear thickness will not be there on the replacement final drive I purchased. I was just hoping that it won't be an issue.

No it won't. I've got an ABS disc on the back of an '83 mongrel.



*Alright. Okay. It was there until I got fed up with looking at it and removed it during a tyre change.

Dai wrote:No it won't. I've got an ABS disc on the back of an '83 mongrel.



*Alright. Okay. It was there until I got fed up with looking at it and removed it during a tyre change.

Great... all good then, just going to swap out the ebay parts and should be good to go in that section of the bike.

From what I have read up thread, these are my observations.  

The final drive is rooted and can be replaced with a new one and the same with the drive shaft (bolt on/bolt off).  The drive shaft is held on with a circlip at the gearbox (transmission in US speak) and it pulled rearwards to unseat it.  This can be difficult, so I suggest you remove the swingarm to make it easier.  There is a rubber boot at the front end of the swingarm, so be careful with this.  Access may be limited, so don't be afraid of removing things if they restrict access.  The drive shaft needs to be the 20 tooth one and not the earlier 16 tooth one.  

I assume the oil leak in the swingarm is the thicker gearbox or final drive oil (80/90W).  By removing the swingarm you will be able to confirm or not whether the oil is from the output shaft of the gearbox.  The swingarm is dry with no oil unlike a R series BMW, so it has to come from somewhere.  The only lubricant in the swingarm is the paste used on the worn shafts.  

As for the rubber bits inside of the swingarm, I have no idea from the information supplied.  

You can remove the ABS disc on both wheels with no effect (three bolts from memory) and refit the wheels. Your ABS lights are probably flashing anyway indicating a fault.  Removing the ABS modules and brake lines is a job for another day.  If the ABS warning lights that flash in the instrument panel annoy you, then place a small piece of tape over them.  The brakes still work if there is a fault but the brake fluid should be replaced and bled before riding.  

Let us know how you get on as it is all fairly straight forward. 

Also when you have the swingarm out, check the rubber boot over the clutch push rod that is at the rear of the gearbox and connected by the lever to the clutch cable.  Replace it as a matter of course as it is probably cracked and can leak.  Unless it looks new, it will have deteriorated with age and heat.  

If you have a manual (Clymer or Haynes) this will help you.

TacKler wrote:Your ABS lights are probably flashing anyway indicating a fault.  Removing the ABS modules and brake lines is a job for another day.  If the ABS warning lights that flash in the instrument panel annoy you, then place a small piece of tape over them.

Alternatively just pull the blue relay out of the relay box.

Altenatively (2); replace the entire driveshaft and bevel drive with the much tougher 16-spline versions. It'll probably turn out cheaper than getting new bits welded up. Yes, it does affect the speedo reading because it's a different gear ratio, but it's so little that it's never bothered me.

Somebody's gonna shout me down

That video takes me back to the 80's when I was working in Hull (UK) and staying in an hotel. I was in the bar when the Quo came in for a few drinks before going for a radio interview. I was still there when they came back and we ended up drinking tequila sunrise till the early hours.

It was difficult the next day trying to fault find on a new telcomms network!

Mike

Used final drive and driveshaft came in yesterday. All is good, thanks for the help ya'll.

TacKler wrote:
As for the rubber bits inside of the swingarm, I have no idea from the information supplied.  

If I recall correctly the drive shaft has an inner and outer with rubber vulcanised in-between. (as shock absorber) The rubber may be from there, with the inner and outer starting to part and loose pieces.

If someone put an incorrectly-phased driveshaft in there, that would account for the shock absorber rubbers breaking up? Or have I miss-remembered how the later shafts work?