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Thread: Stuck Clutch

  1. #1

    Stuck Clutch

    Hi all,

    New here - just bought my first bike, a 1980 R100 RT !
    The bike looks and sounds great, but I noticed right away that the bite-point on the clutch was very high, with almost no room left on the handle lever.
    After my first ride (once the bike was in full operating temp) the clutch wouldn't disengage, and I couldn't shift into 1st without lurching forward, or killing the bike.

    I did lots of digging through the forums, but I still have questions, so please bear with me. Here is what I did:

    1) Adjusted the clutch mechanism to the correct specs. The only difference was that now the whole bike vibrated heavily once the clutch lever was pulled. Oh, and the shift linkage broke because of my attempts at shifting without a clutch.

    2) Replaced shift linkage.

    3) Lubed the splines (no rust detected), the push-rod piston, and bearings. Both seemed to slide off of the back of the transmission fairly easily, thought they were a little harder to slide back in. While cleaning the splines, I also tested the push-rod for stickiness, and it moved back and forth from the back of the transmission through the end of the spline shaft with ease, so I assume that the rod isn't bent or broken (please correct me if my assumption is wrong).

    After the lube job, the vibration seems to be mostly gone, though the engine revs still go down a little bit when I pull the clutch lever. The lever now feels harder that to pull, and the clutch still won't disengage.

    Questions:

    – Sounds like the pushrod piston and bearings need to be replaced (or lathed)... But like I said before, I was able to remove them easily. I can see the piston moving back and forth, but it doesn't look like much, maybe 2-3mm. How far does the piston normally travel? How would one sand down the piston without a lathe?
    – The clutch cable looks healthy, but could it need replacement? If so, can someone explain why? Stretched cable?
    – How stiff is too stiff for a clutch lever on an airhead?
    – Do I need to replace the whole clutch kit (pressure plate, clutch, springs, etc.)? From what I could see, it was pretty clean in there - no shards, grime, gunk, or rust.
    – Any other suggestions or ideas?

    I was a little discouraged that this happened on my first bike - on my first ride - but it's apparent that the airhead community is strong, so I'm hoping you guys can help me !
    Thank you in advance!

  2. #2
    Liaison 20774's Avatar
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    Welcome to the forum and to your first Airhead! The '80 model is the last of the heavy clutches but prior to the early '80s issues with bad valve seats, etc. Enjoy it!

    When you get some time, you might want to browse Snowbum's webpage which has lots of discussions about Airheads. He's verbose and likes lots of different fonts and colors, but it's well worth the read. He has a search tool, so use it to find things. On this page are some discussions about stiff clutches:

    http://bmwmotorcycletech.info/clutch.htm

    As for adjusting the clutch, did you do it like this post? This is from Tom Cutter, independent mechanic BMW trained:

    https://forums.bmwmoa.org/showthread...945#post499945

    I've really only ridden BMWs so I have no comparison for clutch pull, but I don't have any issues with my /7, which should be essentially the same as yours. If you were able to move things easily on the bench, seems like it would work OK in the bike. I do seem to recall hearing about some interference when things get hot, so maybe that is what's going on. Not sure how to tell it might be doing that. Look on the same Snowbum webpage for issues with stiff clutches and hot transmissions...for the '80/81 bikes.

    Certainly a new cable might be a good place to start. BTW...how many miles on the bike? If you have the clutch parts out, you could measure things to see if you're close to spec. But if you get to say 100K miles, might be a good investment to replace it all and give yourself fewer headaches.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Thanks for the response, Kurt!

    I made the clutch adjustments following the same procedure (with the exception of replacing the cable itself)
    I've also been doing lots of reading through Snowbum's site already, which is where I landed where I am.

    I looked into the drum on the pushrod once more to see if it was the culprit, as I think the movement that I saw (of 2-3mm) is probably not enough to disengage the diaphragm spring (just a wild guess). I can't find any information on how much the whole mechanism should travel.

    With that said, the diameter of the drum is okay - 25mm to be exact - under the allowable 28.7m, per Snowbum's instructions.

    I decided to pull out the push-rod this time, and noticed that it was slightly bent right around the thin part where the felt ring sits.
    There is also some scoring along where the bearing and drums sit on the rod.
    However, the rod itself does move and rotate freely...

    I'm thinking of replacing the cable, and push-rod, but I'm not convinced on either as a solution to my problem
    Why would the clutch lever feel so heavy, despite all the parts moving freely?

    Also, what could cause the RPMs on the engine to drop (as much as 750rpm at one point) when the clutch lever is pulled?
    My theory is that the clutch fused with the pressure plate (or flywheel?) during my first ride... thoughts?

    Edit: the bike has 15k on it at the moment. Though who knows, with the 5 digit counter, it could be 115K I was really hoping to avoid replacing the clutch, but Unless any new ideas pop up here, I'm afraid i'll just have to open it up.
    Last edited by penter; 09-01-2018 at 11:52 PM.

  4. #4
    Registered User ebeeby's Avatar
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    Oak had a procedure for stuck clutches but I can't find it and thus can't confirm it applies to your symptoms. Anyone else have it?
    1973 R75/5

  5. #5
    Liaison 20774's Avatar
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    I get that the OPs clutch is stiff to actuate, no really stuck. At any rate, Oak's response to un-sticking a clutch is here:

    https://forums.bmwmoa.org/showthread...=1#post1096500
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  6. #6
    I'd start with a new cable. If the clutch itself is ok, then the only thing that explains this is a stretched cable -- yeah, sounds unlikely but it's low hanging fruit. IIRC, you can take a tire iron and lever the actuating arm towards the transmission. At that point, the rear wheel should turn freely with the bike in first gear. These are dry clutches and there should be no drag when the clutch is disengaged. The only other possibilities that I know of are sticking plates and a badly adjusted EZ clutch but I presume you do not have the latter.
    '61 Clubman's Gold Star, '13 690 Duke, '13 Daytona 675R, '17 1290 GT, '18 Street Triple RS (gone but not forgotten: '76 R75/6, '84 R100, '76 R90S)

  7. #7
    Thanks again y'all.
    There's also Snowbum's method here:
    http://bmwmotorcycletech.info/clutch.htm

    I'll give it another go, with more agression (per Oak's suggestion) this time.
    Getting a new cable as well, to see if that how that helps

    Another question: Assuming that the cable is properly adjusted, if I remove the spring from the actuating arm, does the push-rod push against the arm with enough force to make the cable taught?

  8. #8
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    I had a very hard clutch pull a few months back, slowly feeling harder as time rolled on. I checked everything down low and moved to the cable and found it frayed in the cable adjuster. The felt was also gone and the nylon bushing for the lever pivot was all but gone. Replaced the cable, felt, and bushing with a touch of silicone grease and it is easy and smooth once again. Go to the fiche at Max and look at Diagram #32_0751 for the left handle unit to see the parts for your bike. Hope this helps.
    Dave Hutton '78 R100S (mfg 7/77)

  9. #9
    Registered User AntonLargiader's Avatar
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    With an '80 model, the lathe thing doesn't apply to you. And you have already seen that it's not sticking. And FYI you have a finger spring rather than a diaphragm spring. The diaphragm spring and the larger piston that can stick started in 1981; the entire flywheel and clutch was completely redesigned.

    I have seen the symptoms you describe when the pushrod is broken. Maybe it is and you just don't realize it. Can you post pics of the parts that you can extract? The forward bearing race should be a tight fit around the narrow end part, which is continuous with the rest of the pushrod all the way to the pointed tip that seats against the pressure plate. I have seen them break at the narrow section where the felt goes, and also at the thin end where the bearing race is pressed on.

    The clutch lever effort on the pre-'81 models can be pretty high, and there is very little movement of the pushrod. This is because of the simple spring design; the 1981 setup is a huge improvement. That said there should still be relatively little friction if the cable is good. When you pull the lever in, the force shouldn't be a lot higher than what you feel as you release it. A new clutch cable can really transform the way a bike feels, by reducing the friction.

    The clutch spring will be plenty strong to return the mechanism to 'engaged' up to the point that it can't move any more. The purpose of the rear spring is to keep a bit of tension on the cable when it is fully released. The 2mm of free play at the lever means that the clutch spring force ends before the lever goes all the way out, and BMW doesn't want the cable to be completely slack during normal riding or the cable could come off the clutch arm.
    Anton Largiader 72724
    Tech articles - YouTube
    Virginia Motorrad Werkstatt BMW motorcycle service and repair in central Virginia

  10. #10
    Thanks for the breakdown, Anton - super helpful.

    I think I found the issue, however:

    One of the flywheel bolts wasn't screwed in, and was sticking out.
    This was probably interfering with the spring action. , which explains the heavy vibration when the clutch was depressed.

    Also, not sure how problematic this is, but I found that the conical hole on the pressure plate was much deeper than the one found in the new clutch, probably from so much pressure/friction against the push-rod when the clutch lever was pulled, which is likely what caused the rod to bend, as well.

    Going to be replacing the flywheel bolts, clutch (all parts) and push-rod.
    Also doing the clutch cable, just because.
    Fingers crossed!
    Last edited by penter; 09-23-2018 at 04:02 AM.

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