Clutch release sticking when warm

[Lee]

Hello folks
Newbie to K's - got an R80 and R65 but this is my first time with an air cooled .

Just bought a 1994 K75 , well used (75k miles) , but also well looked after , and I've come across a problem with the clutch .

The cable is quite stiff, and whilst I can get free play at the handlebar lever, the cable is too long at the other end of the cable, and in fact hits the silencer - I have adjusted the locknut adjuster on the release mechanism , and that seemed to adjust OK  according to spec .

However, my major problem is that when warm , the release mechanism gets stuck 'in' and doesnt release , and as a consequence the clutch remains engaged , and the bike cant be driven . After about 10 minutes the release mechanism  releases itself , and all is well again, and the clutch engages well, with no slipping, albeit with a slightly tight cable action as per above  .

I have had a close look, and it doesnt seem as if its the lever pivot sticking , but rather its the mechanism behind the rubber boot .  So I'm thinking that maybe the coil spring has  lost its 'spring', or maybe the thrust piston/bearing (its a combined part now I think?) might be distorted in some way, and so sticking on the pushrod . As far as I can tell, replacing these parts looks very straightforward - I just wondered if any members have come across this before ? (BTW, I understand  that there is meant to  be a little oil from the gearbox behind the rubber boot, and when I prised the edge of the boot off earlier today, it was much more like mayonnaise than oil, so I changed oil and driveshaft oils (the latter looked OK) so that may also help.

What do you think? Any thoughts very welcomed .

[Laitch]

For starters, Lee, work grease into the cable ends where they mount into the handlebar clutch lever and the lower lever. That may make more of a difference than you'd expect. Be sure you have the correct cable measurement at the lower clutch lever—approximate 75mm of exposed cable. Do a complete check of adjustment including free play at the lever.

A torn boot can leak a little. Replacing the boot and spring is often done when input splines are greased. If it's producing mayonnaise, well, you've got yourself a little cottage industry startup.

[rbm]

If the PO had the transmission off and did work to the splines / clutch, it is possible that (s)he has bent the pushrod.  The only way to verify this is to remove the transmission, take out the pushrod and inspect it.  The K75 pushrod only comes out through the front of the transmission unfortunately.

You can eliminate all the other components in the clutch actuation assembly (hand lever, cable, actuator) by testing each one individually. For example, disengage the cable end from the actuator  and test the hand lever motion and check the cable for free motion and no binding.  Pivot the actuator to test its freedom of movement.  If all looks good on the outside, the bent pushrod is the next most likely cause.

[The Mighty Gryphon]

I too had the problem with the clutch cable end hitting the silencer when adjusted for 75mm of exposed length.  I shortened the exposed length with the adjuster about 3-4mm.  This was enough to let me let the clutch lever snap back from being pulled in without getting a clank from the cable end hitting the silencer.  Then do the rest of the adjustment procedure.  I have about 15,000 miles since making this adjustment and so far everything is working as it should, and without the constant clanking as I run down the road.

I would pull the transmission back enough to see the clutch splines to see if they have been lubed.  I have done this to all three of my K's and found that none of them had been done by previous owners.  That spline lube has done wonders to all the bikes I have done it on.  Virtually eliminated hard shifting and the clunking on downshifts these bikes are allegedly known for.  While I doubt it's the source of your problems, I also am pretty sure that a clutch spline lube certainly won't hurt.

[Lee]

Thanks for replies folks - helpful- unfortunately I cant adjust the the cable any more Mighty Gryphon by the adjuster as its already taking up all the slack- I suspect that the cable has  stretched- I'll try greasing it Laitch  , but I think I'll put on a new cable to eliminate this and this may make the cable a little easier . But as I say the biggest problem seems to be a sticking release mechanism behind the boot .I'm currently hoping that a combination of new g/box oil and new spring and thrust piston might do it rather than having to change pushrod  - but I dont understand why the release mechanism would stick in when warm, and then slowly release as it cools down.

I'll keep you posted - thanks for replies- any further ideas very welcome 

Lee

[Laitch]

Thanks for the update, Lee. I'm sure you'll get this sorted.

[Elipten]

Heat causes metal to expand and hence more friction and resistance.  Just an idea.

[Lee]

Hi Elipten.
Thanks for this - I was wondering the same thing. If that were the case , this may well be a warped pushrod being exagerated by heat expansion , which rbm felt was likely . I have had a look at the pivot mechanism and that seems to move freely, and the cable and lever move freely when not connected to the pivot so I definitely think the issue is behind the rubber boot . This weekend I plan to replace the stuff I can replace easily ie spring and thrust bearing , and see what happens .........Lee 

[Elipten]

Best of luck

[Lee]

Hi everyone
Thanks for suggestions on this
I changed the oil in the gearbox , and it wasn't even mayonnaise , more like milk, and I also very carefully adjusted the clutch , and hey presto , it seems to have cured the problem . I took it out on the same run as last week , and whereas last week the clutch was slipping after 3 miles, this time no slippage at all.

The clutch didnt need too much adjustment , and I think it was the gearbox oil which was the key  , given that this  seems to feed the clutch release bearing , and I suspect the bearing was expanding once  warm, and without effective lubrication , was getting stuck on the pushrod, and not releasing  .

I dont know if thats the explanation, but it makes sense to me.

I changed the engine oil and driveshaft, fully expecting milk there also, but they werent at all bad , so maybe some water got into the gearbox through a cable opening .

I have used the bike a few times now, and I must say it's growing on me vs my air cooled twins- I am a steady rider in my mid 50's , and I like the fact that it is very predictable on the road  , it seems to be well put together and overall it inspires confidence when riding it . The fairing is great, and useful given how much it has rained in the UK recently ,although I also have a fully faired R80 so I already knew about the effectiveness of the BMW fairing .  I had read about the smoothness of the triple and I am indeed very impressed  at just how smooth it is .

Anyway, thanks again for your suggestions - and I hope I dont raise this particular one again !

Lee   

[The Mighty Gryphon]

Thanks for the feedback, Lee.  Good to hear you have it resolved.

[Lee]

H all

I thought I had the clutch problem resolved , and it had seemed better , but at the weekend I took the bike for a 10 mile ride and when I got home the clutch release again failed to release .

So, trying to stick to the principle of do the simplest things first , I replaced the release bearing and spring - the bearing was quite hard to get out , and seemed very tight on the pushrod , which  I was pleased about because it suggested that perhaps it had become missshaped or the bearings worn (the new one slipped on like a dream which I hope means it was the bearing and not a bent pushrod) .

The old  release spring was also shorter than the new one, which suggested that perhaps it was worn, which again I took as a positive indicator as another possible cause of my problem.

I took the silencer and rear wheel off to gain easier access , which was all really easy to do .

So far , this seems to have worked - no problems at all, and I took the bike for a long run yesterday.

Fingers crossed , because if it doesnt fix the problem , I guess the next thing to do is to get the pushrod out, which looks like a bigger job .

Fingers crossed

Lee     

[W P Kelpfroth]

Sounds like a problem I had a while back.  The clutch surface doesn't release from the flywheel because of the lack of lube on the clutch splines/transmission input shaft. 

Get a couple M8x125 bolts and cut off the heads.  These will support the transmission during the lube.
Support the bike, disconnect the shock at the swing arm.  Support swing arm.  Loosen bolts on final drive. 
Remove any two transmission/engine bolts and replace with your headless bolts. 
Remove the other transmission bolts and slide the transmission back 5-8 cm.  this is enough to get a small brush with lubriplate or other really sticky lube onto the shaft.  It doesn't take much.  Your guide bolts keep the weight off the transmission shaft during the lube. 
Reassemble and check out.

[Martin]

When I replaced my rear main seal, and did the spline lube I also took the opportunity to drill and fit a grease nipple to the clutch arm. Older vehicles had multitude of grease nipples which has now been eliminated on newer vehicles and that seems to work. But the pivot arm is not sealed at both ends, and is open to the ingress of water and road debris. With a grease nipple you can keep out the water and force out any crap.  It wont solve your problem which I believe is lack of lube on the splines.
Regards Martin

[Lee]

Thank you martin and WP- your thoughts much appreciated .

I havent lubed splines yet - previous owner told me that he had done it not many miles ago , although I am thinking of doing it soon to check that they are OK, and also just to learn how to do it .

In terms of the slipping clutch , I havent had a problem since changing release bearing and spring - the old spring was noticably more compressed that the replacement , and I suspect this may have been the problem .

Thanks again for your suggestions 

Lee