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slipping clutch

Discussion in 'Technical and Troubleshooting Torque' started by kik, Apr 22, 2008.

  1. has anyone had problems with clutch slip developing after an oil change.

    this relates to wet clutches only and im told happens becouse the oil has been changed from a synthetic to a mineral oil, or vice versa, after the clutch was bedded in on the initial type of oil.

    apparently the clutch fibres become contaminated with the oil type that they were bedded in on and dont gel with the other type cousing slippage after the oil type is changed.

    if anyone can confirm or deny this it would be appreciated.

  2. Interesting theory but the problem is they're both still oils and so there should not be any problems with them mixing.
    What could cause problems is incompatibility between the additives used in the oils (though this is rare), or because you're using something not designed for motorcycles that contains friction modifiers (which can cling to the friction plates of the clutch and remain there even after an oil change).
    I've switched between mineral and full synthetic (and vice-versa), even mixed the two in the same engine, never had a problem with clutch slip as a result.
  3. "Car" mineral oils contain friction modifiers that can make a wet clutch slip.

    synthetics generally don't.

    You may be able to clear it by draining and flushing with diesel.
  4. [off topic]

    Oy Ibast, when did you get a 955i???! How you liking it??


    Oh, what they said.
  5. Rob,

    I've had it a few weeks. I'm waiting for the rain to clear in Sydney so I can give it a wash and post a few photos and a review.

    Still got the old girl for the time being too.
  6. Sweet ride. I've always like the look of that bike. Congrats. :)

    I look forward to your observations... a nice relatively modern sports bike with modern suspension... will you still need rear brake to steady the ship so to speak.... :-k

  7. The way I ride anything is on the cards. :p
  8. A friend of mine has a 955i and only puts in the Motul Synthetic specifically designed for bike use with wet clutches, problem is it's about $65 to replace every service.

    If money is no object fair enough however, most wet clutch's are designed for good old mineral oil or semi-synthetic. Basically down to the fact most synthetic oils have friction modifiers and cleaning detergents in the mix and can/will cause clutch slip.

    I hope this next bit helps to understand a little more:-

    The most basic type of synthetic is really a special mineral oil. Known as 'hydrocracked' bases, these are made in oil refineries by
    putting certain types of mineral fraction through special processing, so
    they cost more than the usual mineral types but not much more. They are
    useful because they resist evaporation at high temperatures. Although
    used for years for genuine technical reasons, they are now popular with
    marketing men because the magic sexy word 'synthetic' can legitimately
    be printed on the label without spending much on the oil inside the can!

    Yes, all low-cost 'synthetics' contain anything from a few percent to 20
    percent (i.e. 'semi-synthetic') of special mineral oil.

    Using fairly simple chemical compounds or gases from oil refineries
    or other sources, it is possible to 'synthesise' or build up tailor-made
    lubricant molecules which have very desirable characteristics, such as
    great resistance to cold, heat, evaporation losses or excessive thinning
    as they get hot. These are the true synthetics, and the two that are
    used in engine oils are PAOs (poly alpha olefins) and esters. Neither is
    cheap! PAOs are related to mineral oils, and are the ideal carriers for
    all the chemical compounds used in mineral oils. Because they do not gel
    at very low temperatures, all genuine 0W-something oils have to be based
    on PAOs to pass the 0W test at a sub-arctic -35C. Esters were originally
    made for jet engine lubricants, and to this day all jet oils are
    ester-based. Although similar in performance to PAOs, they have a
    valuable extra trick: they are good lubricants and help to protect metal

    As 0W- and 5W- grades are not usually recommended for motorcycles,
    perhaps the best all-round oil is a 10W/40 shear-stable semi-synthetic
    with some ester content. Esters help with transmission and valve train
    lubrication. 100% fully-synthetic oils are actually quite rare, probably
    because they are very expensive to make, and even more expensive to buy.

    Even so, an ester/PAO with a very shear stable multigrade polymer is the
    ultimate oil for high output engines that are worked hard, which means

    Hope it helps explain oils aint oils
  9. Hi Guys. New poster so plz be gentle with me.

    I have a 10 year old 955i with the same problem. But it only happens at high revs (7000+). Intermittent at first but becoming more regular.

    It has had a recent full service and i noticed the prob a couple of days later.

    I was thinkin i needed a new clutch but this thing about mineral or synthetic oil has given me something to think about.

    Does this sound right? (only happenin at high revs)

    Any help and advise on this matter would be much appreciated.
  10. whoa, nice segue here; the OP is not about clutch slip in a 955i; no bike is specified!!!

    I have always been told what ibast has said; car oils, which do not have to lubricate clutches (and shouldn't) contain additives specifically for engines, and shouldn't be used in wet-clutch bikes.
  11. Sorry. I'll try to be more specific.

    I'ts a Triumph Daytona 955i (t595) with a clutch that has started slipping above 7000 revs.
  12. That's when they start to slip if they are going to...

    You will need to repair or replace:

    1) Clutch plates - metal ones should be flat, no sign of warpage. They can warp through excessive heat through poor adjustment (lack of lever free play, but I think yours is hydraulic and I don't know the exact adjsutment, if any)

    2) Friction plates should be grooved - if worn smooth they need to be replaced and the metal plates, if not warped, should be roughened on the surface. That's not always easy to do...

    3) Check the free length of the springs. This is a critical measurement, since only a mm or 2 will severely reduce the tension on the clutch plates. New springs would be a good idea.

    4) Make sure you haven't used any friction-modified, car-type oils.

    Once a clutch starts to slip, unless it is a case of incorrect free play (which shows by allowing slip to develop with just the slightest movement of the clutch lever) you will have to rebuild the blighter.

    Contaminated oil can not be flushed out of the system to "repair" a slipping clutch, if that was the reason for the problem. Well, it didn't work for me.


    Trevor G
  13. Hi Trev. Thanks for the reply.

    It does sound like the it's on it's way doesn't it.

    Guess i'm gonna have to resign myself to the fact that i've got to shell out fot a new clutch.

    What's confusing me though is there's no sign of it happening at lower revs. Even when you let the clutch out with the brakes full on.

    Again. Many thanks for the reply. Guzgog.
  14. The higher the revs, the more horsepower is generated by the engine and consequently must be transmitted by the clutch. Sooner or later it starts to slip under load.

    It's also not a coincidence that the bigger the load (such as by going uphill, carrying a passenger or just going faster) the sooner the clutch slips.

    Try letting the clutch out with 7k rpm on the clock to see what happens - there is definitley more power the more you rev it! (Better again, don't try it...) ;-)


  15. Cheers Trev. Thanks for the invauable advise.

    No.I dont think i'll try that particular little test though i did actually consider it for a split second :roll:.

    I'll just take your word for it. Don't really fancy a re-build of both bike and garage wall.

    Cheers again. Guzgog.
  16. I should also add that my initial clutch/brake test was carried out at around 2000 rpm not tickover.