Maybe not much difference in viscosity but the additive packages are quite different between gear oil and motor oil.

 

Yes they are different. Just that those that think it is that much heavier should know it really is not. Spectro is great company devoted to motorcycles. I have used their gear lube for years in newer machines . Some older ones the additives are not friendly to brass that maybe used in them.

 

good stuff..when I started racing motocross in the mid 1970's it was an all Golden Spectro and Bel-Ray show..there was no reason to use anything else

 

FWIW...Baker recommends Spectro in their transmissions. I've been running BelRay for the past 20K and am happy with it. Smooth shifting, and minimal clunk.

 

I noticed that, and they recommend 5K fluid changes..at $20 a quart I can't get on board with that but I might try it for 10K see if it makes a big difference or not over the Formula +..sounds like it might..I usually change my trans fluid every 10K like many, the HD stuff at half the price every 5K might be a better idea, 5 K just seems like overkill to me tho

 

Anyone got info on what gear lubes are "not friendly to brass"? It seems odd that oil companies would put out a product that wouldn't be friendly in all differentials. Unless there aren't any in vehicles today that have brass in them.

 

The issue came up with the GL5 syn lubes As temps rise the additives can react with yellow medals. I had a email from Spector years ago. And they stated it was not an issue for any of the newer models. That was around 2007. It was an issue with all GL5 rated lubes at the time .
If I remember right the temp were the problem could occur was 250 degrees.
Keep in mind I use Spector full syn in my transmission. I have sense 2007 It is widely accepted that a GL5 in these transmission is extreme over kill.
I do not have a problem with over kill for a good product.
With changes at 15-20K it comes out looking good. Still red.

This is one of the statements from that time I dug up

"API GL-5 gear oil designates service of hypoid and other types of gears
commonly found in rear axles. A GL-4 oil may be employed in certain manual
transmissions.

These differences are mainly distinguished by the level of active additives
employed in the product. Different applications require different additive
levels and different component materials can be affected by the levels of
additives present in the lubricant.

Having said that GL-4 and GL-5 gear oils are not compatible and
manufacturer's recommendations should be adhered to. They cannot meet the
same specifications and the product performance and tests are different.

Typically, a GL-5 gear oil will have about 2 times the active additive level
of a GL-4 product. This additional additive can cause problems with yellow
metals like brass or bronze."

 

Formula + primary, Bel Ray in the trans.

I have no issue finding N, and if i rev it slightly prior to shifting into first, i never have any clunk and the trans is pretty quite.

Everybody has their favorite for some reason.

 

+10 on the Spectro Full Synthetic 75w140 gear oil in the trans. I change it out every 10,000 miles and never had a problem. It does help to find neutral and make the trans shift smoother.

 

Well I just ordered a bottle of that Spectro Trans fluid. I figure I'll try it out and see if there's any difference. Can't hurt.