Hello,

I would like to convert dura ace fh-7800 rear hub to fit 8/9 speed cassette, my question is, if I buy a new freehub of different grade(example 105), will its cups fit OK with the dura ace cones?
Paying 100 euros for a 7700 freehub doesn't sound too good...

I know usually 10 speed freehubs fit 8/9 cassette, but it isn't the case with fh-7800.

any advice appreciated, THANKS!

no it will not work. The 7800 uses a different style cassette body than all the other shimano hubs. The 7800 hub body attaches like a campy hub body, not the regular splined body that is attached with a bolt

No other cassette body will fit the 7800 hub.

It is possible to machine the splines down to the same diameter as the 8/9 splines and take 1mm off the flange to get the correct length, but the shallow aluminum splines won't hold up well.

The machining is not hard, but machine shop hourly rates are not cheap, so it might cost more than it's worth. One poster on another forum said he's had several done for $25 each, but I wouldn't expect most shops to do it for that, unless they're not busy and work it in when someone has nothing better to do.

Thanks for info. What is the flange part and is it absolute necessary to take 1mm off that?

is the process necessary to do with machine or is it possible to do by hand with file?

in this topic couple peoples have succesfully machined the freehub, no mention of the flange(?):
https://weightweenies.starbike.com/fo...hp?f=3&t=37860

The 8/9 is about 1 mm longer than the 10 speed... so you 'need' to machine down the flange 1 mm more for the cassette to fit in the 'correct' location.

Assuming you have the space between your smallest cog and the chain/seat stays, and you don't mind monkeying around with your derailler position, and the lockring threads are long enough (i imagine they are), then no, you don't need to machine out the extra 1 mm.

In reality if you're already chucking the thing into the lathe, taking out the 1 mm is trivial.

You will not be able to do it by hand. you will need a lathe

Its probably an easy 15 minutes if you have a lathe.

I'm not very smart, but here is my thinking FWIW:

I get a 7800 RD. Does it take my old 8-9 speed chain? If so, I'm fine. If it demands a 10 speed narrow chain, I can add that, and see if it grabs my cogs and chain ring without giving me skippy s**t..

I can either see 8-9 chain or 10 chain grabs or not. Skips. that is crap.

You bring your bike to my shop, and I''ll tell you you're fine, or you have to spend more money to get this baby to work niice. You don't have to spend it with me, I'm rich enough, I just tell you what you should think about doing.

Time for a new set of wheels??

purchase a 10-spd right shifter (sold separately) a new chain and a cassette...Voala....10 spd

The 7800 hub has about 15% (and more) flange distance than most other hubs due to the fact that it's 10 speed specific. That's noticable

So how many millimeters exactly needs to be machined off from the freehub and is it necessary to make the splines shallower or the freehub shorter(or both)?
That's all that needs to be done to fit 8 speed cassette?

I'm doing this because I got the wheels for good price...

Thanks

The cassette body has a step in it. You will need to turn it down to that step. The cassette body also needs to be widened 1mm on the spokes side.