Just curious what people are using. Right now I have HD syn in engine and primary but that will change soon. It just seems like I should be using a higher viscosity in the primary (like gear oil).

 

Changing to a Gear Oil in the primary/tranny is a good idea, but not for the reason you think. Gear Oil and Motor Oil viscosities are measured on 2 different scales. 20w50 Motor Oil and 75w-90 Gear Oil are basically the same viscosity. The difference is that Gear Oil has an additive package that's designed to cope with "molecular shearing" that occurs in a gearbox. Motor Oils have additives that deal with the nasty byproducts of the combustion process.

There's tons of oil info on the forum HERE.

Just an FYI: I run Mobil-1 15w-50 syn automotive oil (yep that's right, see the link) in the engine and Mobil-1 75w-90 Gear Oil in the Primary/Tranny.

 

The main benefits of using gear lube is the additional additive package which helps to reduce shearing/scuffing.

As far as the 'viscosity' of gear lube, many people fail to realize that a 75W90 gear lube has about the same 'thickness' as a 20W50 motor oil. The below chart will give you a better idea when dealing with motor oil and gear lube;



Also, I wouldn't use a motor oil in the manual transmissions of my cars or trucks, and I won't use it in the manual transmission of my bikes either.

There are different API rating for gear lube, ranging from lower protection GL-1 to GL-5 which is rated for 'severe conditions'.. Any GL-5 rated gear lube would work in the manual transmissions on Harley's, but with the Sportsters you need to be a little more selective as the same fluid is used for the transmission and the clutch pack. Because of that you want to use a fluid with a low enough moly content that it won't cause an issues with the clutch. Too high of a moly count might cause issues with the clutch plates.

A good synthetic GL-5 rated gear lube is Mobil 1 75W90 gear lube, and it is used by many that own Sportsters. UOA's show that the moly content is only around 60 ppm, which is less than many 'motorcycle specific' motor oils.

Here is a little more information dealing with gear lube API ratings;

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.

 

Wow, thanks for the link and info. Definitely helpful. I will be switching to gear oil in the not too distant future.

 

Mobil-1 75w-90 Gear Oil.

 

after trying a number of brands and weights. i'm now running mobil 1 sythetic 75w90 gear oil, which gives me the best overall performance on the clutch as well as shifting in all temperature ranges from ambient 30 degrees to 110 degree weather. I used some heavier weight stuff in the past that my dad used in his roadking, which was great in summer, but cold weather gave me some minor clutch issues untill things warmed up.

 

I JUst picked some up at my local customs shop today at lunch. all mine says is Drag Specialties Gear and chaincase oil espeially blended for Sportsters. API GL-5 service rating.
I'll probably put it in on the next rainy day we get. Then I'll let you know how I like it. (i doubt I will feel any difference)

 

Well that's being optimistic. Of course nobody knows what's in Drag Specialties' products since they are a private label and untested.

 

I figured I'd give it a shot.

 

I had always used Amsoil 20-50 in both holes. After reading a lot of info, in the spring of 08 I put Mobil 1 synthetic 75-90 gear oil in my primary 2 times for a total of 4000 miles. For me didn't make a bit of deference. Shifting, noise, smoothness, nothing changed. So I went back to the Amsoil just because it's easier to have one oil around for both holes.
Maybe I have been just lucky with the Amsoil, I don't know. Works great for me. If I ever do have trouble with the Amsoil in the primary believe me everyone will know about it. With a total of around 45000 miles counting my last Sportater no problems yet.