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Thread: Frog Legs ?UNI-TINE? Wheelchair Forks pivot bearing tightening

  1. #1

    Frog Legs ?UNI-TINE? Wheelchair Forks pivot bearing tightening

    I think this has been discussed but I can't find it. I want to tighten the pivot bearing to provide some damping to reduce wheel flutter at higher rolling speeds. I have done this in the past (with good success) with the same model Uni-tine Forks. I recently replaced my Uni-tines after having mine damaged by the airline and they furnished me a new pair. We did not change the caster angle.They flutter horribly at as little as 8mph.
    Now I can't figure out how to tighten them. We took the wheel off and put a socket wrench on the exposed nut which would not budge at all. I don't recall the fork having to come off the chair to do this but perhaps it does. My mechanic friend is out of the country for a couple weeks and I'd rather not try to do this using my wife for working hands unless we have a pretty good likelihood of success. Does anyone have first hand experience doing this? My chair is a ZRa in case that matters.

  2. #2
    I couldn't find the answer, but it should be in the ZRa manual. See chapter 11 if you haven't gone through it already. Isn't what was discussed before is to tighten the wheel spin and not the steering axle (pivot bearing)?
    http://www.wickedwheelchairs.com.au/..._zra_aeroz.pdf
    I have had periodic paralysis all my life. I lost my ability to walk in 2011 beginning with a spinal block, which was used for a hip fracture caused by periodic paralysis.

  3. #3
    I found some old 2009 threads confirming that the problem and solution are exactly what I recalled--just need more dampening. Now I just need to figure out why on my current Uni-tine the adjustment nut doesn't seem to turn. What I didn't try was loosening it first just to make sure that the nut moved and then try to tighten.

    http://sci.rutgers.edu/forum/showthr...ghlight=caster (thread)

    https://www.rehab.research.va.gov/jo...37/3/kauzl.htm (technical paper)
    Last edited by endo_aftermath; 11-05-2019 at 09:49 PM. Reason: fixed link to old post

  4. #4
    I would try that, if it's bottomed out add a washer

  5. #5
    Success! We took the stem out and a spacer was visible between the inner races of the two ball bearings. Obviously, with the spacer in there tightening the shaft wasn't going to accomplish much. I figured we could get the bearings out and just remove that spacer and tighten the bearings carefully to add damping, but wanted to confirm with Frog Legs that that would be OK and that there was not a more elegant solution. I sent an email to Frog Legs customer service and pretty much immediately got a phone call back from Chris. I didn't ask but I assume he's in some engineering/technical role there. He was extremely accommodating and confirmed that my approach was OK, going as far as that if I screwed it up (my words not his) that I could get back with them and they would make it right. We took it apart and removed the inner race spacer and preloaded the bearings enough so that we could not spin the fork a full revolution by snapping it with my hand. The trip down the neighborhood hill confirmed that as fast as I could go created no fluttering. I can feel some added resistance when turning my wheelchair on flat and smooth ground but it's not enough to be an issue. I will gladly trade that to eliminate the fluttering.

  6. #6
    Junior Member
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    Aug 2019
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    Hyattsville, Maryland
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    Quickie Q7.. clueless owner lol my caster will tighten on turns. Becomes very hard and make turning difficult. When completing the turn it starts to flutter.. any ideas on what it might be or where I should start ?

  7. #7
    I have no first hand experience with Quickie forks and casters. Sorry. But if what you are describing is your fork becomes harder to turn when you rotate it one direction, and that would be clockwise looking from the bottom, and easier to turn, even loose, when you rotate it the opposite direction, then it sounds like the stem bolt is self-tightening as the fork rotates. It could do that if the lower bearing has failed and no longer does what a bearing is supposed to do. But take my advice with caution. I may be misreading both your problem description and the part function shown in the Quickie assembly drawings.

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