I've got a 2002 Fat Boy that I'm getting ready to change the tranny fluid on. After much research on the topic I've purchased some Mobil 1 synthic 75W90 gear oil, but now I'm begining to wonder if I should have gotten one of the 75W140 gear oils. I was a bit concerned about the 140 weight and that's why I opted for the 75W90. What are you using and what would you recommend.

 

I was running red line shockproof heavy, but now the local HD stopped carrying it so I went to pick up some Lucas 85/140, but all the auto stores were out so I went with Royal Purple 75/140

 

you will be fine with 75w90. running amsoil 75w90 in mine since 500 miles.

 

You are fine, that is what I run.

 

I run Spectro 75W140 gear oil and it's the best oil in a Harley trans I've ever used...

 

I use Mobil 1 75w90 in the tranny.

 

I run the mobil 1 75/90 as well

 

One more vote for Mobil1 75w/90.

 

In all my years of riding, I've never had to "research" anything other than the owner's manual for the recommended lubricants. Any good quality 4- stroke motorcycle oil will give a Harley transmission all the lubication it needs, and a Harley transmission doesn't even have to share its oil with the engine. I run Mobi1 V-Twin 20w50 in mine.

 

Nothing wrong with a factory fill.