If you have an 748, 916, or 996 then just want to let you know of my recent problem I have been experiencing with my hub, which was not caused by the cush drives backing out. It started a week back when I decided to take the sprocket carrier off to have a closer investigation, first sign of a problem (after fine metal deposits on back wheel) was finding the nut held on lose, fears were confirmed as I found the back of the carrier had grinded itself against the inner part of the eccentric hub.
In case you don’t know the bearings inside the hub are held on by a large circlip, the danger is if you don’t notice in time and the inner hub is grinded to nothing, then the circlip will come out locking your rear wheel!!
Well after closer investigation by Tony Brancato it appears the lost of clearance can be clause by a few factors all off which could set off the other causing the problem to get progressively worse.
1 The circlip within the sprocket carrier wears the grove during use causing the clearance between the carrier and hub to reduce.
2 The bushs within the sprocket wear during use, or move, causing free play within the sprocket assembly.
3 On aftermarket carriers like the Renthal there appears to be no recess to hold the washer like there is on a std OEM rear sprocket, since the washer is only a few mm thick it can distort as the bushs and circlip wears causing free play.
With all of the factors listed the end results is a grinded hub, and a potentially safety issue. Of course if you want to avoid this happening then check your hub assembly regularly-something easier with std sprocket when you need to dismantle the whole assembly every sprocket change, and make sure your sprocket nut is not lose.
Another thing you can do which Antonye has done is to change to the later designed sprocket assembly. For me I am getting the damaged Renthal carrier machined to incorporate a recess, getting a thicker washer machined to fit it and stop any free play in the circlip grove, and replacing the bushes.
Pic of hub: you can see how the part were the circlip is has been grinded away.
http://i.domaindlx.com/karl999r/Hub.jpg Pic of Renthal carrier
http://i.domaindlx.com/karl999r/renthal.jpg Pic of a std rear sprocket: showing the recess for the washer.
http://i.domaindlx.com/karl999r/stdsprocket.jpg [Edited on 13-8-2004 by Karl]