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'88 750 Sport - Mystery Binding Forks On Replacement Front End

Discussion in 'Supersport (1974-2007)' started by 88Sport, Aug 15, 2020.

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  1. Hey Guys

    My forks are binding at slow speed/stationery, which manifests itself in some pretty crazy handling at slow speed and likely interferes with the working of the forks regardless.

    The forks are replacement 900 SL Showa 41mm upside-down forks and were recently serviced by a reputable suspension specialist, and off the bike testing them they exhibit no issues. So not the forks themselves, although I note they are off different bikes not an original pair as the fork lowers are a slightly different colour.

    I have tried every variation the standard loosen the bottom clamps, loosen pinch bolts/ bounce/spin wheel, and done it with bottom tightened and top loose to make sure its not the alignment there.

    Even when I have the top clamp off altogether it still happens,

    The forks slide in an out of the clamps easily, with no great effort so I really think the alignment is good there.

    So wondering may its axle related but again not sure what it would be other than the wrong axle which was pinching the forks but loosening the axle and the pinch bolts doesn't seem to solve it.

    The only thing I've done to the bike recently was check and tighten very slightly the steering hearing head but can't see how that's related other than I took top clamp off but was careful to re-seat it properly and tighten everything.

    So a mystery but posting here just in case anyone has experienced something similar.
     
    #1 88Sport, Aug 15, 2020
  2. When you say binding, is that on compression only or rebound only or both can you ascertain? Depending on the forks, have you tried both or either of these at the lowest setting? Did the specialist use standard spec oil or go heavier?
     
    #2 Chris, Aug 15, 2020
  3. It’s on compression, although it appears to happen after the rebound stroke. It’s weird but if there’s enough motion and downward pressure it works.

    Not 100% on weight oil but would be spec for the Showa, think it was 5 or 7.5.

    It doesn’t happen with heavier pushes on the top clamp but with lighter ones, which is reflected by the way the bike behaves on the road with slow smooth roads it seems to bind.

    I’ve completely removed the forks, tried both on the lowest settings (fully open). Tried changing the position of the forks in the clamps as well but same deal.
     
    #3 88Sport, Aug 15, 2020
    Last edited: Aug 15, 2020
    • Thanks Thanks x 1
  4. sound like the forks are being pulled inwards when wheel spindle done maybe loosen the spindle and see if free up check if spacers are correct as you say they are replacement forks
    just a thought
     
    #4 johnboy, Aug 15, 2020
    • Agree Agree x 1
  5. Agree - what's it like with the front axle loose?
     
    #5 Keith_P, Aug 15, 2020
  6. Have done a lot of stuff today and one of the things was to loosen the axle a little (not fully just not torqued) and it still did it. I will try loosening more in the morning but why has this just started happening? The only thing I’ve done different is slightly tightened the steering head.
     
    #6 88Sport, Aug 15, 2020
  7. Is it really binding or are the springs too stiff for your weight making them feel as if they're sticking? But, ok, this is only since you've tightened the headstock bearing.... Back to basics maybe - loosen the headstock and check? Wierd.
     
    #7 Keith_P, Aug 15, 2020
  8. Yep tried that. The springs have been specifically set for my weight and were working ok, although not perfect.

    I backed off compression and rebound and tried no preload and full preload.

    I tried it with absolutely no top triple, still binds so likely axle related but fuck knows why that should suddenly become an issue.

    I can’t understand how playing with top triple/steering head would suddenly cause this but that’s the only thing I’ve touched.
    [​IMG]
     
    #8 88Sport, Aug 15, 2020
    Last edited: Aug 15, 2020
    • Like Like x 1
  9. commiserations, this is a strange one. Since you had them back and fitted, they were behaving ok/almost ok at one point? For how many miles/how long roughly. Have you got the opinion of the specialist who rebuilt them yet? The only clue I can think of from tightening the headstock bearing - when you study the "active" part of the fork legs, are they showing consistent finish e.g. v. good chrome or slightly matted chrome for the whole perimeter plus/or does it show more "matt" appearance on fully compressed area? I wonder if one of the legs or fork cases/upper tubes are slightly distorted. To follow this theory, particularly if uneven wear on chrome apparent (if you've just had rechromed etc then hard to see or comment) then it might be worth swivelling each fork assy 90 degrees if desperate just to see if performance changes.
     
    #9 Chris, Aug 15, 2020
  10. Shock Treatment in NSW first asked me to check the top clamps weren’t over tightened, and to check that the forks were ‘floating’ something about inserting a flat blade screw driver somewhere. Not really sure what to do there. Will likely just trailer the bike up there next week.
     
    #10 88Sport, Aug 15, 2020
  11. They probably meant you to open up the fork-top clamps a bit using flat screwdrivers to give some 'float'...
     
    #11 Keith_P, Aug 15, 2020
  12. [​IMG]
    the forks are the type where the axle threads into the fork.
     
    #12 88Sport, Aug 15, 2020
  13. The forks seem to be exhibiting normal wear. It feels like it could even be some form of hydraulic lock. It’s only done about 1000km since servicing. This hasn’t happened quite this bad before but from memory now there has always been a slow speed turn issue that I thought I’d sorted just with reducing compression.

    Here’s a video to explain it slightly better
     
    #13 88Sport, Aug 16, 2020
  14. Good & clear video. Simple action would be to remove the dampers if, as you say, you suspect a possible hydraulic problem. A little radical, but not too hard if I remember (I dismantled my '98 900SS forks)...
    That would remove all doubt about it being a mechanical alignment issue, which it looks like it's not.
    Weird.
     
    #14 Keith_P, Aug 16, 2020
  15. The only thing that stops me doing that is that I’ve had the forks off the bike and they seem to work fine when compressed manually. So in retrospect it would seem unlikely it was hydraulic and even if it is I don’t have the time or knowledge right now to pull them apart and know what I’m looking at. I will take it back to shock treatment who charged me handsomely to service them the first time around. Frankly I’d love to fit a new set but finding a decent second hand pair will be tricky.
     
    #15 88Sport, Aug 16, 2020
  16. They'll respond differently off the bike, as the mass of the system is so much less. Seems like a good plan to get them (on the bike) back to the servicer. You can demonstrate the (repeatable) problem as per your video. Have you any idea if the problem goes away or reduces when they've warmed up? Could be an issue if you ride the bike to them & there's no problem anymore.
    As they did the service, there should be no reason for them not to get involved.

    You're kind-of not saying clearly whether this problem was 100% there before the service. Was this the reason for the service originally? Could be that they've always been bad - perhaps with erroneously-fitted damper internals (discs?) - and have simply been rebuilt the same...?
    Urgh - a pain...
     
    #16 Keith_P, Aug 16, 2020
  17. Needed new springs, too hard before. They weren’t great but not this exact problem.
     
    #17 88Sport, Aug 16, 2020
  18. If they definitely don’t show the fault separately / off the bike.
    - Slightly bent axle or one of the fork tubes is not quite straight (roll on a known flat surface to see rise / fall) ?
    Possibly before you correctly torqued up the steering head, there was enough give between upper and lower triple to move to allow both forks move slightly relative to each other and to compress under light load but now that is tighter, it is magnifying the misalignment and binding.
    - clip ons or yoke pinch bolts too tight - Relatively soft alloy outers compressing onto the moving inners
     
    #18 Jon Wright, Aug 16, 2020
  19. I tried with top clamps only tight to eliminate the outer potentially interfering with innards (bottom loose) and pinch bolts loose, axle not torqued, and the same thing happens. The forks slide neatly in through both clamps. Already tried top loose.
     
    #19 88Sport, Aug 16, 2020
  20. As already suggested, I think it could be the axle pulling the forks in when tightened. I’ve seen it before when a front end was a mix of parts. The earlier speedo drives were different and in the case I had, the original drive was too narrow. The new forks may have a narrower foot than your originals meaning that the drive would need to be thicker to make up the difference. Can also cause brake binding?
    Do the axle up and then slacken the pinch bolts off on the left leg, the one with the threaded insert. Give the front end a good bounce and see if the insert pulls into the leg?
     
    #20 nelly, Aug 16, 2020
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