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Minimum Freehub Body Spline Engagement

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Minimum Freehub Body Spline Engagement

Old 02-18-21, 12:04 PM
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70sSanO
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Minimum Freehub Body Spline Engagement

I have an '88 Cannondale and ever since MiamiJim posted a thread about fitting a 10 speed cassette into 126mm dropouts it has been my goal to accomplish a similar project. I'm able to easily run an XT732 7 speed freehub body on a FH-7700 hub. Note: I realize that many here have just shoved a 130mm freehub into a Cannondale with no issues, I really don't want to go that route. Even if the Pope posts and says that is what he does, I'll pass.

I imagine no one has done the following, but for the sake of argument is, here goes.

The depth of a typical spline on a freehub is around 5mm and the body is around 5.5mm. There are deep and shallow freehubs with corresponding bodies. Using a shallow body on a deep cut freehub results in the cassette stops being too close to the flange and therefore the spokes. While MiamiJim primarily used thinner spacers/washers and locknuts, it might be possible to add a .5mm or so shim washer between the freehub and the freehub body and use a shallow freehub body. This will help with a potential first cog to dropout problem, but it does reduce the effective spline length that engages the freehub body and the freehub. I'm wondering about the minimum spline engagement.

Below is a pic. The freehub on the left is an XT732 with the 7 speed freehub body. The one on the right is an XT732 with a 760 body and a .5mm shim washer.



John
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Old 02-18-21, 01:06 PM
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If I understand your question correctly, you are wondering if adding a .5mm washer under the freehub would cause any problems.
In my experience, it has not.
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Old 02-18-21, 01:39 PM
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Originally Posted by rccardr View Post
If I understand your question correctly, you are wondering if adding a .5mm washer under the freehub would cause any problems.
In my experience, it has not.
Thank you!

That is pretty much the gist of the question. It “might” end up closer to 1mm, which reduces the spline engagement from 5mm to 4mm. It all depends on the low cog spoke clearance at the flange. I’ll probably want a minimum 1mm clearance.

I’m retired or I would run this by the engineers where I worked. The XT freehub in the pic has steel splines and the DA-7700 I’m planning on using are aluminum. If they were steel I wouldn’t bother asking.

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Old 03-01-21, 04:07 PM
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This past weekend I decided to convert my DA FH-7700 to an 8/9 speed and fit it into my 126mm dropouts on my Cannondale. About a year ago I removed the 9 speed titanium freehub body and installed a 7 speed freehub body from an M732 freehub. In the first post the freehub body on the left is the 7 speed from the M732 and the one on the right is the 9 speed from an M760. In the end it ended up at 127.2mm since I needed to place a spacer behind the cassette and needed a bit more chain clearance on the DS.

I added 2 shim washers totaling .8mm between the 7700 freehub and the M760 freehub body.


I built everything back up and the distance from the spoke flange to the end of the freehub body is about 1mm to 2mm less than the distance for a correct freehub body. The downside from using a shallow flange freehub body was the clearance from the spokes at the flange to the large cog. It was less than 1mm.


I temporarily installed a 7 speed 14-34 cassette with a 1.3mm spacer behind the cassette for more spoke clearance and everything shifts fine. One of my concerns was being able to move the FD cage inward enough to not get chain rub with the more inward large cog location, and not drop the chain. I'm going to try and install a 13-36 8 speed cassette with 8 speed shifters in the next week or so.



John

Last edited by 70sSanO; 03-01-21 at 04:13 PM.
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