1977 r80 clutch slip

Discussion in 'Airheads' started by madoc, Apr 16, 2021.

  1. madoc

    madoc Adventurer

    Joined:
    Jan 3, 2009
    Oddometer:
    26
    Location:
    Herefordshire
    I bought a 77 r80 at the end of last year. It has been standing for around 15 years, but has some history before that but nothing clutch that I can see.
    I sorted out a fair few electrical issues, completely stripped/cleaned/rebuilt the carbs, complete refurb of the calipers and M/S, replaced some perished rubbers on the forks and final drive etc. etc etc

    It starts, runs, sounds and handles fine BUT the clutch slips something awful when cold. Give it a few miles and then she's fine. I've adjusted the clutch cable/arm according to a couple of sets of instructions (which are pretty similar to be fair) and also backed the arm adjuster, on the transmission, a fair bit out but no real effect. The clutch disengages fine and is light in use.
    There aren't any oil traces externally to indicate leakage inside.

    I don't know why the bike came off the road originally. Mileage is very much unknown, but it's ex-plod. It's been stored somewhere nice and dry tho, as there was no aluminium, chrome or paint damage.

    Is there anything else I can look at externally, before pulling the gearbox ? Could this be the throwout bearing ?
    I'm tempted to ride it and see if it sorts itself, after all it's been stood a while with the plates glued together. I've had british stuff, in a similar state which sorted themselves after some use.
    #1
  2. oldgsbob

    oldgsbob Been here awhile Supporter

    Joined:
    Jul 20, 2011
    Oddometer:
    147
    Location:
    Surrey, England
    I'm wondering if the clutch arm on the back of the gearbox is sticking in but slowly releases. You could check the free play there before you use the clutch then again after one opreration of it, of course when it is cold.
    #2
  3. Disston

    Disston ShadeTreeExpert Supporter

    Joined:
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    Oddometer:
    18,820
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    Silver Spring, Md
    Seeing if it sorts itself out sounds like a good idea at this point. When cold and in it's slipping mode I'd say avoid higher revs where it's going to slip.

    It does sound like even if you can avoid an expensive new clutch now it will need one eventually.

    EDIT: Removing the transmission is not as bad a deal as most think. You may find the input splines were over greased or the rear engine seal is the culprit in which case all that's needing is a good cleaning, new seal and less spline lube. So just thinking this period of letting it sort itself out maybe best not being too long. 10 shorter rides, 1 or 2 hundred miles.
    #3
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  4. Dreossi

    Dreossi Been here awhile

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    Apr 21, 2013
    Oddometer:
    567
    Location:
    London, Ontario, Canada
    It’s possible that the push rod is hanging up in its travel. You can draw it out, clean and lubricate it, and check the condition of the felt ‘seal’ that’s in there. You can check the thrust bearing etc while you are in there.

    I’m not sure if your bike has the older felt arrangement or the ‘newer’ plastic bushing- someone will chime in- but if either are dry/dirty the clutch pushrod can hang up. The bore on some of the plastic bushings need to be slightly enlarged in some cases...best done on a lathe.

    I use the grey anti seize lube for these components during assembly.
    #4
  5. Disston

    Disston ShadeTreeExpert Supporter

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    Oddometer:
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    Should be a felt seal push rod, '77 bike, not easy to remove and sometimes impossible to replace from the rear with the trans in the bike. The thrust pieces and tiny roller bearing of the push rod arraignment are easily removed.
    #5
  6. Pokie

    Pokie Just plain Pokie.

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    Don't pull the pushrod unless you are prepared to pull the transmission as well. As Disston says, it's nearly impossible to get the pushrod back in from the rear. Seeing as the clutch acts funny while the engine/ transmission is cold, I would figure the difference is either oil related or expansion related. Is the clutch arm well lubricated? Does the clutch arm move freely with the cable removed? How about the throw out bearing, sometimes the seal lip will double over, making the throw out move reluctantly. Doesn't sound like the clutch plates, they usually show slippage when hot.

    If everything seems good, as a last resort, you could go ahead and pull the clutch pushrod from the rear, remove the felt, slip the pushrod back in and try that. If the problem either goes away or stays, at least you now know it's not the pushrod. Course, putting the felt back on and reinserting the pushrod will require pulling the transmission. While the transmission is out, inspect the clutch drive splines, if they are dry and worn looking, that alone may have been the problem.
    #6
  7. Plaka

    Plaka Brevis illi vita est

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    you need to do the clutch splines anyway. this does not demand pulling the tranny but you will get to do other good stuff, like put in a better neutral switch, grease and torque swing arm bearings, inspect and grease shock eyes, etc. so may as well go at it.
    #7
  8. madoc

    madoc Adventurer

    Joined:
    Jan 3, 2009
    Oddometer:
    26
    Location:
    Herefordshire
    Don't you just hate it when there is no solution posted, to help those in future.

    I gave up and got the clutch out. Done it before and a few times with urals/dneprs/changs.

    The friction plate was 3.8mm, which is well below the service limit of 4.5mm (new one was, I think, over 6mm)
    There was friction plate dust caked everywhere. No trace of oil. Splines good, pushrod felt seal pretty worn too.

    After a good clean up, I replaced the friction disk and also the diaphram plate (although it was useable). New clutch bolts, new drive shaft bolts and pushrod seals. @ £140 in bits, but that should see me out.

    I guess around 4 hours all up, with a significant amount of that remembering how to get the gearbox in/out with the limited clearance and faffing with the drive shaft bolts and boot.

    You will need a clutch centre-ing tool and a reduced socket for the swingarm.

    Normal service has been resumed.
    #8
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