I figure this is aimed at me... They're slipping. As in no drive in the upper gears. The noise level was the same, just the thing was slipping. The Barnett clutch went in more to change the noise, and improve the response than because the OEM basket was worn - which it was, a bit, but not enough to be a 'have to' job. I never considered that 20,000kms between sets of plates was that unusual for a 900?Punch
Yes Brad had you covered I will agree with him that outside of breaking a post hubs do NOT wear out. I change them about never unless there is tip over/crash damage or it is an move to a slipper clutch, other than that I have not seen a reason to change one. Outer basket is another story in that the grooves can get so deep the plates hang up and the pack does not separate enough, this too can be remedied with a file to make the basket continue but as you gain space between the plate tab and the basket you increase the wear rate and noise level.
As to aluminum vs steel.
steel hubs do exist but they are probably 1980's and earlier so I doubt you will have one anyway. The aluminum hubs have a large steel washer that is under the "cup" this washer can wear into the hub on early models but all you do is add another of the same washer if you have this issue. Later models have a insert so it no longer wears into the aluminum hub.
Steel baskets can run any type of plate, aluminum or steel.
Aluminum baskets SHOULD run aluminum plates but sintered plates will be steel, as far as I know all slippers running sintered plates run steel plates in aluminum baskets. I did a 848 dry clutch conversion last year and the "kit" came with non-sintered plates on aluminum, clearly street focused which will lead to shorter friction material life.
Steel baskets ring, Aluminum baskets thud. Pick your sound and enjoy, though remember us mechanics are running your bike on a bench with that open dry clutch at ear level ......What......what did you say?
The 749/999 kit should bring your bike up to latest spec for a dry clutch it should last a good long time. At that price it should be a bargain and just a drop in. make sure to Loctite those outer basket bolts or oil will weep through the threads and cause a leak.
When you said you are only getting 20,000km out of a oem clutch what was wrong with it? I have oem clutches going 50,000 miles that are only changed due to noise. Seriously 20,000km is probably jut time for a bit of clean up, you may be doing the same as selling a bike instead of giving it a tune up. Yes noise will grow with age but the clutch should be fully functional well past the time you want to listen to it, I have a 50,000 mile plate on the wall that has about 1/2 tab worn off but friction material is about 80% and I know it would run fine.