Sharkey has it right.

The transmission is full of gears.

Shouldn't one use a -gear oil- in it?

 

And why is it necessary to change the transmission lube as often as the engine? I can understand changing it especially the first time to flush "break in bits", but every 5 K??

 

Change it every 10K is fine....hell I do mine at 20K!!

 

in my 2008 Dyna low Factory Service Manual it states trans and primary change every 10k. Check your maintenance schedule.

 

I use Red Line Shockproof too for the tranny.

 

Red Line worked great in my 5 speed. I just use HD oil's now; much easier on the road miles from home. I know I'd probably never need trans oil when touring, but I also know the HD dealer network is my best bet for service on the road 3000 miles from home. (We have shipped our bikes, then flown to ride our own; a seperate thread)

 

I run Amsoil in my 2014 FXDF and will not go back to anything else. My bike runs better and cooler. Best oil as far as I am concerned. The 4 products I use are
20/50 v twin syn
V-Twin primary fluid syn
V-Twin trans fluid syn

 

Wow, I do mine every year...lol. I ride a lot but the New England weather permits for a short season, (5000+ miles) I work at night and get out very late, the ride is peaceful but one must be on high alert, the large 4 legged critters hop out of nowhere.

 

Just ordered the full Amsoil trio for my 1K service.

I went with Amsoil Severe Gear 75w110 for the trans.

 

This is what I run. Made specifically for 6-speed tranny. Expensive, but I really like it: