I've been using 75-90 full syn gear lube in primary on my 89 FXSTC, is that bad?

 

Barnett says don't use synthetics with their clutch plates but if you aren't having any problems then I wouldn't worry about it.
Personally I think you are overspending for your primary fluid but hey your bike your choice.

 

Not to mention that its incredibly thick.... I run ATF in mine.. 75-140 in the trans..

 

 

just to be nosey Been using the gear oil long?

WP

 

I use HD primary oil its good stuff. Bell ray in the trans, mobile 1 in the crank case.

 

Hate to hijack a thread but I have to replace the primary gasket sometime this weekend because of excessive leaking so I'll be watching this discussion

 

About a thousand miles.

 

I went to a Harley dealership and got formula+ primary and chain case lubricant. Not synthetic. My opinion is that gear lube is made for gears not primaries. If I were you I'd drain yours and replace it with the right stuff at risk of destroying your clutch

 

This atf idea interest me.
I have a home machine shop and use a lot of atf as cutting fluid, it's cheap, plentiful and I can get it anywhere.