My local HD Dealer claims harley is now making and selling and recommending 80 weight transmission gear oil instead of 20/50 oil like the motor.
What are any of your thoughts?

 

I've been using it for 2,000 miles. I feel it's no better than the Formula+ it replaced. I won't buy it again!

 

80w90 (75w90, or whatever) was used by default until relatively recently. If you read on forum some even espouse 85w140 or whatever the super heavy gear oil is, though I personally wouldn't go that far.

 

I have it in one of mine now also. Will probably go back to Red Line.

 

OWNERS, not engineers, have believed for a long time that a lube designed for a given purpose was best for each application. Engine oil in the engine, gear oil in the transmission, and primary lube in the primary. Harley seems to be coming around to agree with the owners. After that, the choice is yours. I don't understand the Harley recommendation for a straight weight oil, that seems to disregard 80 years of progress with multi-weight oils. Why start with something as thick as honey when it is cold that thins out to a water consistency when hot, when oils that remain more viscosity stable are available. The guy who believes that 85w140 is "super thick may not understand how this stuff works. When cold, it gets no THICKER than Harley's straight 80 weight but when hot it gets no thinner than a 140 weight lube while the straight 80 becomes quite thin. At room temperature, pouring a 75w90 out of a bottle would look no different than pouring an 85w140 out of its bottle. At high temperature the 75w90 would be only slightly thicker than the straight 80 but considerably thinner than the 85w140. They all get thinner as temp goes up, the multi-viscosity, not to the same degree as the single weight oil. The LOWER NUMBER says they will all be about the same before you start the engine, but the multi-viscosity oils won't thin as much at operating temperature,

 

I changed out all my fluids last Saturday, including HD’s 85/140 hypoid oil for the tranny. So far it seems to work just fine, though I can’t really tell any difference from what was in there before. I used their primary oil with the same result, so all I can do at this point is shrug.

 

So, unless I'm missing something, there should be no reason to manufacture or ever use 80w90 gear oil and it should be completely replaced by 85w140--call me skeptical or cynical, or both, but I don't have that much faith in the purported qualities of multigrade oil.

Incidentally, there are clearly some cases where lube designed for a given purpose is better or necessary for that application. According to above assertions a person should be able to run 5w40 oil in an automatic transmission but I'd bet you wouldn't get very far. Admittedly the additives are different, but that alone shouldn't cause a failure for some time, and regardless is further proof that application is important.

In a related example, full time 4wd New Process transfer cases in domestic pickups in the 1970s had a chain driven component, and lube specified was 10w40 motor oil instead of gear oil. At that time most people were used to using gear oil for manual trans and transfer cases and when they ran it in the NP203 it stretched the chain and wrecked the sprockets requiring an expensive repair. Yes the difference in viscosity rating is significant in this case, but again application is obviously important and OP was asking about running dedicated gear oil in trans as opposed to 20w50 engine oil so we're talking significant differences at both lower and higher temps. I'm told the viscosity ratings aren't exactly comparable between engine and gear oils but the gear oils are supposed to have additives designed for that application...

Re Harley primary I'd been given to understand 10w40 motor oil was the standard for years and see no reason to change to dedicated primary lube, but given the insistence by some of its superiority I'd guess the specialty lube might have additives that work better with clutch. Lots of bikes with wet clutches seem to be fine in oil shared with engine though.

 

Way I see it, Harley sells an oil that's marketed as engine oil and one that's marketed as a clutch and trans oil. Manuals also call for that differentiation. Common sense also matches. However, they do list that their engine oil is compatible with the trans and clutch...so. YMMV. Furthermore, Harley's are the exception in the motorcycle world where most use the same sump to lube the engine, trans and clutch.

Clear as mud? Thought so.

Do what you like. I run Formula+ in my primary, will be going to a 75w90 gear oil in the trans next time and will be using whatever 20w50 synthetic I feel like in the engine.

 

Gear oils and engine oils are measured differently. So while the numbers sound different, they are actually very close to each other in viscosity.

 

Yuuup! 75w90 gear oil is nearly identical in viscosity to 20w50 engine oil