New owner here trying to get educated on oils. My question is this: Why does Harley not recommend running gear oil in the trans? It seems to me that they designed the bikes and must put them through the ringer to see what works. Have we thought of something that they are oblivious to. It concerns me that if I don't run what the manual calls for then if it fails they will come back and say I didn't us the right stuff. But, when I went to get my 1k service the advisor recommended Syn 3 and Bel Ray products in the other two holes, which I did.
I don't know if I have the best in there at this point because I noticed the other day on a long ride in hot weather and some stop and go traffic that my trans had more noise when shifting, almost like the gear oil was breaking down...is this normal in hot temps? I am heading to Vegas next week then turning around for sturgis so I am thinking about dumping everything and going with Mobil or Amsoil.
Thanks for any info or where to look for more on the topic.
Doug-Newbury PArk, CA
09 Ultra Classic/Flame Blue Pearl

 

I went from Syn3 to Mobil 1 20w50, then to redline with shock proof additive. I noticed a significant change for the better (smoother and quieter each step up). In my opinion, gear oil is the better choice, but remember what they say about opinions

 

The motor oils used in the tranny meet GL-1 specs and that is all that is required in these bike trannies. The question is if I put a GL-5 gear lube in, isn't that better? It has more extreme pressure additives in it? Logic says yes and maybe the extra EP is what is helping with reducing some noise, along with the fact that most are using a 140 or higher gear lube. More viscosity=more protection, althought you don't want too much or it induces more drag.
The other thing to think about when choosing a motor oil or a gear lube. One is made for a combustion area and the other is not. In motor oils, they add emulsifiers to blend any moisture that may accumulate from condensation. As the engine runs at operating temps, the water is evaporated off. In gear lubes, they do just the opposite and add demulsifiers. They don't want the water mixing and getting between the gears. Water is compressible. So in this case the water stay separated. With the vents, if it gets to high temps, will hopefully evaporate out.
There's an advantage to both.

 

The gear oil vs motor oil thing comes up alot. First if you do a search here there are hundreds of posts on this. So there's a chart that shows oil weight cross reference's and it surprises people to find out 90 wt gear oil is the same weight as 50 wt motor oil. It's just rated on a different scale. 110 wt is like 60 wt oil and 140wt is like 70 wt. The additives they use in gear oil are not what a motor needs, but by adding them, that allows motor oil to be used in the trans. Amsoil has a gl-1 rating which is what most light duty trans require, so mobil1 and syn3 must be rated the same. There are other ratings up to gl-5 which are for trans and rear end use. They newer Harley 6 speeders trans have gears that are cut that make it have more gear whine then the older trans ,and some say using a gl-5 rated gear oil helps quiet the whine.But it just masks the noise it doesn't repair or fix it. Also the trans runs cooler then the motor does, so the oil doesn't get as hot .So the oil should remain in grade. Alot of guys post that by changing the primary oil to a lighter wt like 10w40, or 15w40 even atf helps shifting. The reason for that could be that 20/50 wt oil creates drag on the clutch plates so the clutch doesn't release completely even when the lever is pulled in. That can cause it to bang into 1st gear or when shifting gears. more of a problem when cold. Another thing you'll notice is no matter whose oil you use in the trans ,it will come out looking like new when compared to the motor or primary. Like I said there have been lots of posts you'll have to read and form your own opinion on what works for you.,,

 

I don't use a "motor oil" in the manual transmissions in my cars or trucks, and I won't use it in the manual transmissions on my bikes either.

Here is a breakdown of the various API Ratings for Gear Lube.

Decide for yourself what means your needs, but I'll stick with a good GL-5 rated fluid in all my Harleys.. I happen to use Mobil 1 75W90 gear lube myself (which is GL-5 rated), but many other fluids will work just as well.


API GL-1, oils for light conditions. They consist of base oils without additives. Sometimes they contain small amounts of antioxidizing additives, corrosion inhibitors, depresants and antifoam additives. API GL-1 oils are designed for spiral-bevel, worm gears and manual transmissions without synchronizers in trucks and farming machines.

API GL-2, oils for moderate conditions. They contain antiwear additives and are designed for worm gears. Recommended for proper lubrication of tractor and farming machine transmissions.

API GL-3, oils for moderate conditions. Contain up to 2.7% antiwear additives. Designed for lubricating bevel and other gears of truck transmissions. Not recommended for hypoid gears.

API GL-4, oils for various conditions - light to heavy. They contain up to 4.0% effective antiscuffing additives. Designed for bevel and hypoid gears which have small displacement of axes, the gearboxes of trucks, and axle units. Recommended for non-synchronized gearboxes of US trucks, tractors and buses and for main and other gears of all vehicles. These oils are basic for synchronized gearboxes, especially in Europe.

API GL-5, oils for severe conditions. They contain up to 6.5% effective antiscuffing additives. The general application of oils in this class are for hypoid gears having significant displacement of axes. They are recommended as universal oils to all other units of mechanical transmission (except gearboxes). Oils in this class, which have special approval of vehicle manufacturers, can be used in synchronized manual gearboxes only. API GL-5 oils can be used in limited slip differentials if they correspond to the requirements of specification MIL-L-2105D or ZF TE-ML-05. In this case the designation of class will be another, for example API GL-5+ or API GL-5 LS.

 

Thanks for all the info....great stuff to know and I appreciate your time.

 

Just a quick add-on....I had my 1k service done and have since put 1100 miles on it in 2 weeks...The syn3 oil ain' lookin too good to me. Already smells and is getting dirty. No way I am taking a trip to Vegas in a week with that in there so I am going to change it before I go...can't hurt right?

 

I changed for the better a couple of times with my '07 in the 45k miles i've put on it.

My current fluids are Amsoil 20-50 in the engine, B&M trickshift (ATF fluid) in the primary, and Redline Heavy shockproof gear oil in the transmission. the bike shifts much better and the clutch works great with this combo. I was next to a crotch rocket at a stop light the other day, when we both shifted into first, I could hear his clunk louder than mine!

 

won't hurt to change it more frequently than recommended, only hurts the wallet (and maybe the environment depending upon how you dispose of your used oil)

It is convenient to use the same stuff in all three holes, but by using three different things, you get three different colors, so if there's ever a spot on the garage floor, you'll know where it came from.

 

Lots of different combinations you can use, but the picture below is what I prefer;