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  1. #1
    Disco Infiltrator Darth Lefty's Avatar
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    Freehub swap advice?

    I found a wheel I'd like to use, which has a 7-speed, early 90s vintage Deore XT hub. It's basically unused so far as I can tell. I'd like to use it on my 8-speed, 2002 vintage, high mileage Acera bike. So I want to swap their freehubs. Anything subtle I need to know?

    Any dishing change?

    Any reason I should bin the 8-speed and get a new one? It has a lot more miles on it, but is that a problem?

    Should I keep the left bearings from the Deore and the right from the 8-speed or do anything else clever?

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    Quote Originally Posted by Darth Lefty View Post
    I found a wheel I'd like to use, which has a 7-speed, early 90s vintage Deore XT hub. It's basically unused so far as I can tell. I'd like to use it on my 8-speed, 2002 vintage, high mileage Acera bike. So I want to swap their freehubs. Anything subtle I need to know?

    Any dishing change?

    Any reason I should bin the 8-speed and get a new one? It has a lot more miles on it, but is that a problem?

    Should I keep the left bearings from the Deore and the right from the 8-speed or do anything else clever?
    Shimano has been using the same freehub/shell interface for decades, so just about any Shimano body should fit. If you stick with one that has the same number of speeds, and use the same length axle there's no redishing of the wheel needed. OTOH, if you go with a wider body, or lengthen the axle accommodate a wider frame, then you'll need to redish.
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    swapping to the taller 8spd body will offset the hub towards the non drive side, requiring a redish towards the DS to recenter the rim.
    know that this will produce a weaker wheel, as the disparity of tension between sides increases.

    I'd just use the 7spd hub as is, 7/8 cassette spacing is so similar the 8spd shifter should work on a 7spd cassette just fine,
    and do you really need the14 tooth cog when the upper and lower gears are still the same between 7/8 ?

  4. #4
    Team Water Andy_K's Avatar
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    Quote Originally Posted by FBinNY View Post
    Shimano has been using the same freehub/shell interface for decades, so just about any Shimano body should fit. If you stick with one that has the same number of speeds, and use the same length axle there's no redishing of the wheel needed. OTOH, if you go with a wider body, or lengthen the axle accommodate a wider frame, then you'll need to redish.
    I've never noticed you being wrong on mechanical matters, but I find myself scratching my head over this one. I went the opposite direction last year (put a 9-speed freewheel on a 7-speed hub) and I don't remember having to redish. The original hub used 130 OLD spacing, and it stayed that way with the new hub. It seems to me that as long as the axle spacing doesn't change the number of speed that the freehub can accommodate shouldn't matter. So if the OP puts a 7-speed freehub on an 8-speed hub body, I'd expect just a few extra millimeters of axle showing but no need to redish. Am I making an incorrect assumption somewhere?

    BTW, when I did my hub transplant I think I kept the non-drive side cone and dust cap from the original hub body but used the parts from the new freehub on the drive side.

  5. #5
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    Quote Originally Posted by Andy_K View Post
    I've never noticed you being wrong on mechanical matters, but I find myself scratching my head over this one. I went the opposite direction....
    If you read the post, you'll note that I stayed away from specifics such as freehub body width or axle lengths. I tend to avoid specifics because I'm not inclined to try to remember all the details of every component made, nor to create some kind of database. I couldn't tell you whether an 8s freehub is wider than a 7s one, and I leave that to those who use this stuff daily (I don't own any Shimano equiped bikes).

    This is why most of my posts on this kind of question describe what one should look for and consider, but not provide that actual data.

    In the OPs case IF he uses a wider freehub body he'll need to lengthen the axle, or he might choose to lengthen the axle for his frame, even though the freehub doesn't require it. So IF he does anything that changes the R/L position of the shell on the axle, he'll need to redish. Otherwise, not.

    BTW- I approach mechanics differently than most. Rather than trying to remember tons of details, I try to understand the design principles involved, and know the general lay of the land. Then I apply that theory to decide a practical solution to individual cases as I come to them.

    For example While many buy torque wrenches and look up specs for various bolts, I let my educated fingers tell me when I'm coming to the proper torque.
    Last edited by FBinNY; 12-31-13 at 03:58 PM.
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    Quote Originally Posted by Andy_K View Post
    I've never noticed you being wrong on mechanical matters, but I find myself scratching my head over this one. I went the opposite direction last year (put a 9-speed freewheel on a 7-speed hub) and I don't remember having to redish.
    He's not wrong. An 8/9/10-speed freehub body is wider than a 7-speed and will move the entire wheel toward the non-drive side of the frame. Typically when you make this change, assuming you keep the same OLD, you have to remove a spacer from the nds side of the hub ande recenter the axle and then re-dish the rim toward the drive side to compensate. If you found you didn't have to change the dish after the swap I suspect the dish wasn't right to begin with.

  7. #7
    7-speed doomsday prepper ThermionicScott's Avatar
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    Quote Originally Posted by xenologer View Post
    swapping to the taller 8spd body will offset the hub towards the non drive side, requiring a redish towards the DS to recenter the rim.
    know that this will produce a weaker wheel, as the disparity of tension between sides increases.

    I'd just use the 7spd hub as is, 7/8 cassette spacing is so similar the 8spd shifter should work on a 7spd cassette just fine,
    and do you really need the14 tooth cog when the upper and lower gears are still the same between 7/8 ?
    +1 (of course )
    Quote Originally Posted by chandltp View Post
    There's no such thing as too far.. just lack of time
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  8. #8
    Team Water Andy_K's Avatar
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    Quote Originally Posted by HillRider View Post
    An 8/9/10-speed freehub body is wider than a 7-speed and will move the entire wheel toward the non-drive side of the frame. Typically when you make this change, assuming you keep the same OLD, you have to remove a spacer from the nds side of the hub and recenter the axle and then re-dish the rim toward the drive side to compensate.
    I could easily be remembering this wrong, or something might have been screwed up to begin with, but I would think that the freehub body width doesn't matter at all provided (a) you don't move the left-side nuts, (b) the axle is long enough that the lock nut clears the freehub in either configuration, and (c) you don't change the OLD spacing. I think these things were all true in my case, but I'm not certain.

    Anyway, I don't mean to lead the discussion down a rabbit trail of speculation. I was just trying to understand things a bit better.

  9. #9
    Disco Infiltrator Darth Lefty's Avatar
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    I'd report back but it turns out I can't find all my cone wrenches. Later this week maybe... To be clear this is all 135mm MTB stuff, there is no re-spacing or cold setting or any other extreme efforts.

  10. #10
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    Quote Originally Posted by Andy_K View Post
    I could easily be remembering this wrong, or something might have been screwed up to begin with, but I would think that the freehub body width doesn't matter at all provided (a) you don't move the left-side nuts, (b) the axle is long enough that the lock nut clears the freehub in either configuration, and (c) you don't change the OLD spacing. I think these things were all true in my case, but I'm not certain.
    You forgot something. The width of the freehub sets the distance from the right side of the shell to the right locknut. A wider freehub would push the shell to the left so one of your constants would have to give. Either some spacing would need to be removed form the left, or the axle would need to be longer.
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  11. #11
    Disco Infiltrator Darth Lefty's Avatar
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    Quote Originally Posted by FBinNY View Post
    You forgot something. The width of the freehub sets the distance from the right side of the shell to the right locknut. A wider freehub would push the shell to the left so one of your constants would have to give. Either some spacing would need to be removed form the left, or the axle would need to be longer.
    That's why I asked about dishing in the first place, but it looks like Andy_K might be right. Looking at my 8-speed bike and my BIL's 7-speed bike, the 8-speed has very little clearance to the right of top gear, only enough for the chain, but the 7s bike has a lot, as though the extra length in the 8s hub is hanging off to the right rather than dished out to the left. Will report back when I have a chance to actually try it.

  12. #12
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    Quote Originally Posted by Darth Lefty View Post
    That's why I asked about dishing in the first place, but it looks like Andy_K might be right. Looking at my 8-speed bike and my BIL's 7-speed bike, the 8-speed has very little clearance to the right of top gear, only enough for the chain, but the 7s bike has a lot, as though the extra length in the 8s hub is hanging off to the right rather than dished out to the left. Will report back when I have a chance to actually try it.
    It sounds like someone switched freehubs or otherwise modified spacing in the past. Normally hubs are made with minimum clearance between the 1st sprocket and the frame (or locknut face). That's because the objective is to minimize dish, and any wasted space on the right increases dish.
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  13. #13
    Disco Infiltrator Darth Lefty's Avatar
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    Quote Originally Posted by FBinNY View Post
    It sounds like someone switched freehubs or otherwise modified spacing in the past. Normally hubs are made with minimum clearance between the 1st sprocket and the frame (or locknut face). That's because the objective is to minimize dish, and any wasted space on the right increases dish.
    Straight from the Trek factory.

  14. #14
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    Quote Originally Posted by Darth Lefty View Post
    Straight from the Trek factory.
    Something doesn't add up.

    IME all hubs are set with the smallest sprocket as close to the dropout as possible. Typically the distance from the outside face of the 1st sprocket to the locknut face is just about 4mm, leaving room for the chain and a small air gap.

    This has been true ever since the sprocket clusters were wide enough to need dished wheels.
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  15. #15
    Senior Member Bill Kapaun's Avatar
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    Quote Originally Posted by Darth Lefty View Post
    That's why I asked about dishing in the first place, but it looks like Andy_K might be right. Looking at my 8-speed bike and my BIL's 7-speed bike, the 8-speed has very little clearance to the right of top gear, only enough for the chain, but the 7s bike has a lot, as though the extra length in the 8s hub is hanging off to the right rather than dished out to the left. Will report back when I have a chance to actually try it.
    Are they both using the same size top cog?
    Different tooth counts will provide different clearance.
    Different bikes can also provide different clearance.
    Try swapping wheels and see if you have same/mixed results.

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    The DS bearing race is in the freehub body. Your 7s XT body's race is most likely nicer than your 8/9/10s Acera body's, and would be even if both wheels had the same mileage. (I say this also from experience of swapping a 600 Ultegra triciolor UG body for an STX HG body.) Consider running a 7 of 8 setup with the nicer 7s freehub body. Also if you switch bodies, keep the 7s body clean so you can give or sell it to someone else. (I would have loved a clean XT body for my old tricolor UG wheel.) Watch the cone/seal fit -- you might want or need to match the DS cones to the freehub bodies (IIRC the tricolor cone seal fit the STX body rather loosely and an STX cone would almost certainly not fit a tricolor body well.)

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