I think it's a case by case basis ( no pun intended ) with each bike having it's own preference and here's why: In clutch of the Harris Scrambler, Type F gives the absolute best results possible, Dexrons not so much and engine oils On the other hand anything other than engine oil really really sucks for use in the clutch of Timex.
So there has been a bit of debate over what type of fluid to use in the primary cover. Several people have claimed that Type F trans fluid is the way to go. Well, I'm here to say that Type F blows in the primary. I was using Type F before and bad clutch problems and didn't think anything of it. After my clutch rebuild I used Castrol Import Multi-Vehicle and my clutch worked great, seldom slipped and overall worked just fine. Well, I decided to pull the primary cover and do a bead of silicone to try and get my leaks under control and filled it back up with Advance Auto Parts Type F. I didn't even get out of my parking lot before I noticed the clutch slipping like freaking crazy. It was bad, REALLY bad. So bad that I basically came straight back home, drained the fluid, put about 10 ounces of lacquer thinner in the primary and sloshed that around for a bit, drained that, went for another ride with the primary empty and the clutch is still slipping.DO NOT USE TYPE F IN YOUR PRIMARY!!!IT WILL CAUSE YOUR CLUTCH TO SLIP!!!Scottie J