Some time ago I was able to remove the 688 drop-out bearings (8mm inner race) in my 2006 Stumpjumper, and in some days I will remove the ones in my Ghost ebike and I am posting below the process I am following.
The 688 drop-out bearings will need to be pulled out from each side of the frame’s forged drop-out with a 8mm sleeve anchor:
* Push the 8mm sleeve anchor into the 688's 8mm inner race.
* Place a tube or socket, which is slightly larger than the outer diameter of the 688 shell.
* Screw a 6mm bolt, flat washer and nut into the sleeve anchor.
* Tighten the bolt while holding the sleeve anchor with pliers so the inner race is not allowed to rotate. The sleeve anchor will wedge into the inner race of the bearing so it can be extracted.
* UPDATE 20230420: The biggest issue with this method is to screw the bolt that opens the anchor and tightens it inside the bearing inner race. The inner race rotates so to tighten the bolt you have to grip the anchor with a plier, but it is quite difficult to grip it. So I just soldered a 10mm NUT to the Sleeve anchor and now I can easily grip it with a hex wrench. See pictures below
* Now tighten the nut slowly against the washer and it will pull the sleeve anchor with the bearing attached to it.
* For the opposite bearing you can repeate this process or push it out from "inside" because now there is no other bearing.
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