I have a few quarts of Mobil 1 LS synthetic gear lubricant 75w-90. I live in the So Cal desert, were it get HOT, Is there a GOOD REASON NOT to use this 75w-90 oil in the Transmission & Primary of my 97 Fatboy? Thanks

 

tranny = yes, primary not so much, it wiill work but ATF is cheaper, all you need is chain lube

 

Mobil 1 Gear Lube is an excellent choice for the gearbox.

Don`t use it in the primary. The designation LS is for limited slip differentials, meaning the lube has a friction modifier added to it. It may allow the clutch to slip.

I second the motion for Automatic Transmission Fluid in the primary. Which type? Simple, I use the same ATF as my car and truck use to avoid mixups (Mercon V).