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Thread: juddering

  1. #1
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    juddering

    Hi All, a question please, when I pull away in a hurry I get a juddering shaking the dash board, I can feel each cylinder firing but smooths out when the revs have picked up a bit, this does not happen with a gentle pull away bearing in mind I am always two up, is this normal or should it be smooth even with a hand full of throttle from the start off ?
    Keith
    Oh p.s. a new belt was fitted 500 miles ago.
    Last edited by oslin; 11-08-2017 at 09:16 AM.

  2. #2
    apriliaforum Junkie AndyT's Avatar
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    Hi Keith. The transmission should be smooth even with a big handful of throttle. My GT is, even when pushing it in sport mode. So the question is, what was done at belt change. Juddering could be down to belt slip or possibly clutch slip or maybe a sticking variator. Was the belt done by a dealer with all the right gear to do the retraining? If it was, I would be inclined to take it back and get them to look at what they did. You didn't say how many miles the bike has done. If it is higher mileage, I would tend to look at the clutch rather than the belt. Worn shoes, a glazed housing or just a lot of dust loosened during the belt change (and not cleaned out) could all be potential causes. Have you pulled the cover off and cleaned out the filters? You could also try using an airline through the fan intake to blow any dust out before resorting to a strip down again.
    2009 Mana GT ABS; Andreani fork cartridges with uprated springs; Dorsoduro hand guards and heated grips; 30mm handlebar risers; Digital tachograph: Modified woodcraft folding brake pedal; R&G frame sliders

  3. #3
    apriliaforum Junkie AndyT's Avatar
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    Check out this thread and see what Pete says. He's far more experienced with this than I am. Clutch noise on acceleration.
    2009 Mana GT ABS; Andreani fork cartridges with uprated springs; Dorsoduro hand guards and heated grips; 30mm handlebar risers; Digital tachograph: Modified woodcraft folding brake pedal; R&G frame sliders

  4. #4
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    Hi Andy, thanks for the reply,
    The belt was fitted by Robinsons Foundry, I am sure the clutch is not slipping, if it was re trained or not I do not know, I will try and blow the dust out before taking it to my local dealer who used to be an Aprilia dealer but is no longer, but tells me he still has all the tools etc to service it including the belt, the bike has done 12000 miles with a full service history and it was first registered in 2010, it is the only bike I have ever bought unseen but with good photos and a chat from a dealer in Kent and living in Kings Lynn I do not want to go all the way down there with it, this is the first auto bike I have ever owned out of 31 bikes so far so I appreciate the help Andy.
    Keith

  5. #5
    apriliaforum Junkie AndyT's Avatar
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    Just to discount it - did you check the front sprocket? I've heard of them being so worn that they slip in the chain under heavy load. At 12000 miles it should be fine, but always worth checking the easy things first. Can you feel the gear changes in any of the auto modes? It should be smooth so any feeling of 'steps' or jerkiness might indicate a bike that has been run in manual mode and has worn CVT cones. In the absence of anything obvious it looks like your dealer will have to check it out. I guess repeating the retraining might be worth a try, I know Pete swears at the PADS system due to its failings, but it could just be that the various steps mentioned in my linked thread have not all been done during the belt change and it needs to be checked over thoroughly. Unfortunately that will be an expensive option if you don't go back to the original dealer.
    2009 Mana GT ABS; Andreani fork cartridges with uprated springs; Dorsoduro hand guards and heated grips; 30mm handlebar risers; Digital tachograph: Modified woodcraft folding brake pedal; R&G frame sliders

  6. #6
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    Hi Alan,
    No I can not feel the changes it is smooth both up and down I only get the juddering from the start off and only if I give it the beans, on a gentle pull away it is fine or to put it another way I can hardly feel it, to explain it another way it feels as if the clutch is engaging at too lower engine revs so you get the sensation of each cylinder firing under load but goes when the revs pick up slightly, there is no slip from the chain and the sprockets look fine,
    I had a chat with the bike shop and they could not shed any light on it, but did ask if the belt was wearing more one side than the other, I was going to have a look today but I note the rear footrest mount has to come off and possibly the starter motor etc etc so I think I will leave it for another day when I have plenty of time as it is not going to be quick to check it out.
    Keith

  7. #7
    apriliaforum Junkie AndyT's Avatar
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    Does the clutch drop out at about 12-15mph when coming to a stop and allow you to free wheel?
    2009 Mana GT ABS; Andreani fork cartridges with uprated springs; Dorsoduro hand guards and heated grips; 30mm handlebar risers; Digital tachograph: Modified woodcraft folding brake pedal; R&G frame sliders

  8. #8
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    Yes it does Alan, I ran it up in the garage today on the stand with the back brake on and the juddering is at the same timing as each cylinder firing

  9. #9
    apriliaforum expert pete roper's Avatar
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    So the belt was replaced but did they perform the re-training operations for the wear potentiometer and TCU?
    Professional Goat Burster.

  10. #10
    apriliaforum Junkie AndyT's Avatar
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    I don't know Robinsons Foundry so can't comment on their work, but this is beginning to sound like the CVT isn't opening up enough to get low gear initially so the bike is trying to pull away in too high a gear. Its OK on low load as the clutch slips and masks the problem. Looks like you might need to get the retraining done.
    2009 Mana GT ABS; Andreani fork cartridges with uprated springs; Dorsoduro hand guards and heated grips; 30mm handlebar risers; Digital tachograph: Modified woodcraft folding brake pedal; R&G frame sliders

  11. #11
    apriliaforum Junkie AndyT's Avatar
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    Hi Keith, I was out on a run today and tried to replicate your problem at low speed. And failed. I could feel the engine firing and there was some vibration when holding down the speed with the brakes while keeping the clutch spun up enough to engage, but never got it to translate into a judder. So I think doing the retraining might be what is needed.
    2009 Mana GT ABS; Andreani fork cartridges with uprated springs; Dorsoduro hand guards and heated grips; 30mm handlebar risers; Digital tachograph: Modified woodcraft folding brake pedal; R&G frame sliders

  12. #12
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    Thanks Andy, It only happens on pull away with a hand full of throttle if I take off gently it is fine and all the gear changes are smooth both up and down, it feels just like I have dropped the clutch out at too lower revs on a normal bike, I am beginning to wonder if it is me or as you say the belt need re training what ever that is and I suppose the dealer will have to do that ? how do they do that ?
    also I suppose it could be dust in the clutch which I feel is a real possibility as you have said, its a pity the whole thing has to be taken down just to blow it out, I did check the filters as you suggested and they are clean and there is no dust to be seen in the outer casting at all, I also note it is a lot better solo that two up, less weight I suppose, no comments please :-) but neither of us are heavy people.
    when I mentioned belt re training to my local dealer he looked a funny way and made no comment, bearing in mind he used to be an Aprilia dealer and still has all the tools and has two Mana's in the showroom all be not GT's I thought that was odd ?
    Thanks for all you help so far Andy.
    Keith

  13. #13
    apriliaforum Junkie AndyT's Avatar
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    Unfortunately the Mana's electronic CVT is a mystery to a lot of mechanics, even those who work on scooters with mechanical versions. Basically it is two pulleys with a belt between. The pulleys each consist of two cones (See Pete's sticky belt change thread) which can be held varying distances apart. So when they are close together they effectively have a large diameter as the belt is forced out to the edge and when they are further apart the belt can settle nearer the centre.

    The variator controls the effective size of the first pulley and a spring controls the second. There are various sensors that measure and control the position of these cones relative to each other. As the belt wears the computer senses it and makes an allowance for the wear, so the effective gear ratios remain constant, and then warns you when the wear has got to the point that it can no longer compensate for.

    If you simply replace the belt without doing the retraining the, computer is still working on the compensated dimensions rather than the new and presumably larger ones of the new belt. This translates in practice into the variator holding the first pulley cones too close together, which forces the new thicker belt further out than intended, resulting in first gear being too high a ratio. Under low load this is masked by the clutch slipping a little as it takes up the drive until it bites fully. At full throttle the engine tries to spin up faster so there is less time for the clutch to slip until full bite, but the gear ratio is off hence the judder. A bit like trying to set off in second gear.

    Aprilia's PADS computer hook up is needed to do the retraining which involves putting the bike on its centre stand (or a paddock stand) and starting it. The computer runs it through its speed range with the rear wheel spinning at road speeds while stationery in the workshop, so it's not surprising that the average mechanic is pretty wary of this process. Add to this the fact that the PADS is complex and seems to be difficult to get set up correctly it is not surprising that it might not be done correctly or even skipped completely (mechanical CVTs don't need retraining so a scooter mech might not realise it needs to be done).

    If your dealer has the PADS system they should be able to do the retraining without needing to dismantle anything as it is simply a computer hook up. It's worth trying it before embarking on a strip down again. Pete's belt change thread shows how involved this is and why it is expensive to do.

    Hopefully I covered the basics here, but happy to be corrected by Pete or anybody if I missed anything or got it wrong anywhere.
    2009 Mana GT ABS; Andreani fork cartridges with uprated springs; Dorsoduro hand guards and heated grips; 30mm handlebar risers; Digital tachograph: Modified woodcraft folding brake pedal; R&G frame sliders

  14. #14
    apriliaforum expert pete roper's Avatar
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    There are two re-training functions one to guage pulley positions and one to zero, or normalise or whatever you want to call it, the refference point of the wear potentiometer. Both have to be done with the belt change or you're pushing shit uphill with a pointy stick!

    Pete
    Professional Goat Burster.

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    Thank you both, I think I will have to have a chat with the dealer and if he gives me a blank look again I will have to take it to a current Aprilia dealer thanks again guys.
    Keith

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