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Weird rebound on rear shock

Discussion in 'Technical and Troubleshooting Torque' started by Milpool, Sep 20, 2016.

  1. So tonight when riding my GPX250r to a friend's place I hit a pothole. Apart from being really unpleasant everything seemed to be fine though.

    On the way home I did start to notice every little bump a lot more than usual and after getting it home I realised there was almost no rebound in the rear.

    It sinks down like usual but takes ages to return to normal height when I get off the bike where it used to spring right back up again. There is no damper adjustment on the springs so I can't change anything there. Is this time to replace the rear shock? Is there anything else I should be worried about? Also is it dangerous to keep riding it like this?

    Also for what it's worth, the front suspension seems fine.
  2. Look for oil around the shock, sounds like you blew a seal.There is an old joke there somewhere.
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  3. Is it leaking any fluid out of the shock, a large jolt could have blown a seal on it?
    They do wear out and if its compressing all the way in with minimal resistance its time to replace...I need to do the same on my zzr250 which is on its way out and making funny noises.

    It wouldn't be catastrophically dangerous to ride and I'd personally be ok with it for commuting until the part comes in however certainly not for going through the mountains on as it will affect the bikes handling, like anything you be the judge...if you have any hesitations don't ride it.
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  4. Thanks guys. I haven't removed the fairings for a proper look yet but I did notice a bit of fluid/oil in the general area, not heaps though.

    I think while I'm replacing parts anyway, I might order a shock from the newer ninja 250, apparently it's a nice upgrade for not much money.
  5. Maybe you've bent the shaft of the damper and it's sticking.
    It does sound like time for a new one.
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  6. normal compression and slow rebound sounds like it's bottomed out, and the rebound shim stack is not opening, or not opening much.
    doesn't need to leak to be stuffed.
    if big leak or no oil, then there would be no damping of movement (unless rod is bent as above)

    replace shock. chance to upgrade.
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  7. Thanks again for all the help guys. I've been looking into replacement and I'm relieved to see it's such an easy job to do. Now to look around and see what's available.

    If I do replace with the newer Ninja shock I do expect to notice even more how soft the front end is, but will it be so bad that the bike will start to behave dangerously or unpredictably?
  8. Very interesting Oldcorollas, I have seen one shock that did what the OP described which had leaked out all the oil.
    When you sat on the bike it would bottom out and once you got off it would sort of return to normal, I figured the spring around it provided some minimal amount of rebound....either way replacing it was the way to go.
  9. The damper doesn't provide 'rebound', it damps the springs movement and prevents wild oscillation.
    The spring provides the suspension, taking energy to compress and releasing the energy to rebound.

    Gas pressurised dampers do have some 'springiness', but it's not a significant factor in the suspension. The gas pressure is to keep the oil as a liquid and prevent foaming.
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  10. why not change the front fork spring spacers, effectively increasing the pre-load? (step 1)
    this will mainly reduce sag, but will also give you more travel and the spring will increase in rate at the end of travel.
    you really need to set your sag regardless of any other changes. just need a pipe of the right diameter and length

    you can also increase oil weight, to provide more bump damping. (step 2)
    you can also increase the volume of oil in the forks (a bit), which will decrease air volume at the top pf the stroke, and increase the force from the "air spring". (step 3)

    after that, you can change the fork springs for something with a higher rate (step 4, more spendy)

    easy and simple changes
  11. So I've replaced the shock with another stock factory one. I know they aren't great but I don't plan on keeping the bike much longer as I upgrade my license in February. The replacement works great however and has fixed the problem. Thanks for all the help guys!
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