When I got the 9 blade, I got the clutch with it, so I just installed the complete unit. Same for the OE 5 blade. I never swapped out any clutch from any other fan. After some research, I found out that the viscous fan clutches do not disengage at high RPMs. I was under the impression that they did, but I was wrong. So the faster I went (higher RPMs) the 9 blade was screaming or roaring big time. The clutch on the 9 blade felt a lot tighter than my old 5 blade, but it still was free spinning. I can not and never could hear my 5 blade fan at all. I guess its no mater anyway as I brought the 9 blade back and got the electric fans anyway. Its just to hot to mess with the install for now. Mid 90s in the afternoon. Not to mention, I need to make brackets,and do the wiring. As for the OE 5 blade, it has always keep the truck engine temp cool. I was just trying to make the AC work better. The 9 blade did help some, but I know the E-fans will work better, and will help engine performance at high RPMs some too.