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Thread: Gearbox problem.

  1. #1
    We've had a major gearbox problem this year that involves 2nd gear just jumping (slipping) into neutral by itself, we even disconnected the solemnoids of the pneumatic shifting system we run (since 2009) to see if the solemnoid was activating by itself but still slips out of 2nd gear to neutral.
    I looked around and found out that this problem usually occurs on CBR600 (thats the engine we use) when the 2nd gear cogs are old. So we open up the engine and found out that actually the edges of the internal gear, or counter-shaft gear were badly beveled.
    So we change up the gear shafts for another one we had in other engine and this time it started to slip 2nd after only 2 day usage.
    So we obviously decided its nothing related to the gearbox, but something external that wears the gears up to the point that it makes 2nd gear slip.
    We have some things in mind about the cause of the problem, one of the things that looks most convincing its that the pneumatic system does not have enough power to fully engage the gears, so after time it wears them out. So the only difference between 09,10 and 11 car its the lever arm length, and the 11 lever was lot smaller than previous.
    Thanks for your time

  2. #2
    Have you looked at everything in the gearbox?

    On the end of the shifter drum is the star gear thingy (gear shifter drum guide?), that a roller operates in, which also centralises the drum.
    When you wear the peaks of this, or the spring pressure drops this can also cause the box to jump out of gear.

    Start thingy clearly visible below

    Also, how old is the oil?
    I assume since you changed the gear set that it is fresh oil.
    Nothing is impossible. Improbable yes. But not impossible.

    Swinburne University of Technology

  3. #3
    Yes we checked pretty much everything in the gearbox, including the drum. We pretty much changed everything from a engine that was shifting great, thats why we believe it might be something external to the engine. Thanks for reply

  4. #4
    The problem is only in 2nd? Or is it the 1st - nuetral - 2nd shift that is the problem? Any problems when shifting from 3rd to second?

    Does it slip or jump - theres a big difference. If its alright when the engine is cold but begins to slip more with heat, it might be clutch related.

    I'd take the entire pnuematic system off to eliminate it from the problem.

  5. #5
    I dont think its a clutch related problem because 2nd gear cog its actually pretty bad after problem, so it must be something related with something else. Yes its only 2nd gear that slips , and when it does it couple times if you disconnnect the pneumatic shifting system it will slip 2nd even though (although we know that is because the 2nd gear cog its way to damage) what it is difficult for us to find for know the what causes the 2nd gear cog to wear that fast. I dont think it might be clutch related cuz weve tried 2 different engines know that worked before on other cars, so it must be something on the car causing the problem.

  6. #6
    Look into the barrel and shifter forks as well.
    The second gear fork may have been previously damaged from the pneumatics, and such doesn't fully engage the dogs on second.

    Or spark erode a dove tail onto the dogs to stop them from jumping out.
    Nothing is impossible. Improbable yes. But not impossible.

    Swinburne University of Technology

  7. #7
    Is the semi-circular clip that axially secures the large bearing on the output shaft in place?

    If it is missing the clamping from the block halves is enough to keep everything in place for a short time - after some running you will get results similar to what you are experiencing.

  8. #8
    As Boffin said, definitely check the barrel and related parts of the gearbox.

    But, if that checks out OK, you need to consider that you pneumatic shifting system may be causing the issue. Check on the "Gear Shifting Advice" article on Hewland Engineering website. Has some good tips on how to best shift a sequential gearbox. Do you use ignition cut, and/or clutch, while shifting?

    Dog clutches need to be engaged very rapidly to prevent damage, if they grind at all they will wear out quickly. Once they are worn and rounded off, that can cause it to pop out of gear.

    To that end, you might want to consider that your pneumatic system is not shifting quickly enough, or with enough force. It may seem counter intuitive, but increasing the force may reduce the damage to the dogs. The fact that you are having a problem with second gear indicates to me that it is likely that your shifting system is having trouble making it through the 1-N-2 transition.
    Damon Pipenberg
    gt motorsports 2006-2010

  9. #9
    The forks are wear but they start wearing after the problem starts, and that we think its because the gear its trying to slip and the fork its keeping in place so the cog grinds the fork.
    We do think it might be something related to the the force we are implementing into the system, one test we are going to do its to increase the force of the system by increasing the lenght of the lever that its connected to the shifting shaft that moves the butterfly (or weavy wheel) that regulates drum position.
    We dont use clutch for shifting but we've never have used them, and pneumatic shifting have just caused problems in 2010 and 2011, but in 2008 and 2009 it ran fine.
    The thing that actually its different between its rear track, and lever leght. Rear track might be inducing the axles to go into a elastic mode that induces vibrations into the cogs when down shifting on heavy brakes, these vibrations always existed but they got worse after we increase dramatically the rear track between 2009 and 2010, which amplified the vibrations.
    The other difference as I said before was the lever length that connects the pneumatic actuator with the shifting shaft, in 2010 it was lot smaller (the lever length) and in 2011 it is the same length as 2010.
    Sorry if it gets a little confusing on the explanations, as we are from South America English its not our first language.
    Thanks for all reply so far!

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