I would stick with the 20w-50 that is widely recommended. I use Amsoil 20w-50 that is specifically meant for HD transmission. No, I do not sell Amsoil. Just been a mech for 30 years.

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The MoCo has finally caught up with decades of conventional wisdom and started recommending 80w140 synthetic gear oil.

Proper oil for the proper application.

 

It’s a synthetic gear oil. It will be just fine in the trans. I would recommend using gear oil in there over motor oil. I run amsoil v-twin transmission oil in my bike. Either way, the oil you mentioned will be just fine.


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Red line has a special primary and tranny oil, for what it cost I can pay for the best.

 

Use Belray for tranny, Redline elsewhere.....

 

I have been using 80-140 gear oil. Just purchased Redline V twin gear oil with shock proof to try - it's supposed to quiet the gear noise and help with clunking when shifting. I'll find out soon.

 

Run lighter oil in primary, helps shifting and 1st. gear clunk. 10-40 Castrol Motorcycle oil good for clutches.

 

I use ATF in the primary. Just like NP207/208 transfer cases.

And not that I've ever had any leaks on this bike, but if I did, I would be able to tell straight away where the leak is coming from.

Red = primary.
Sulphur smell from gear oil = transmission
Normal oil = engine.

 

I use ATF in the primary. Just like NP207/208 transfer cases.

And not that I've ever had any leaks on this bike, but if I did, I would be able to tell straight away where the leak is coming from.

Considering change to ATF. Should I pull clutch apart clean the oil off the plates and friction plates. With a cloth? Don't know if its compatible with ATF ??

 

I didnt bother.

Although I have replaced the clutch with a Barnett extra plate clutch since I've started using ATF.

 

I've used the Valvoline Syn Gear Oil since 2006, Go For It!

 

Sportsters are kind of unique in that the "transmission" oil is also the primary oil. So it needs to be safe for clutches, no friction modifiers. Big Twins don't have to worry about that.

 

While it was not synthetic.
I have used gear oil/grease since 1984 in my 4spd Shovel.

Old school Biker taught me.
Never understood why the MoCo originally used an "oil".