Is there any problem using a GL-5 Gear oil in a 2004 FLHTCUI transmission? Only reason I ask is a friend has some Spectro 6-Speed in his 2008 Street Glide and that is absolutely the smoothest shifting transmission I have ever been around. He has an extra quart of the six-speed Spectro but it is GL-5 and the HD 5-speed transmissions call for GL-1.

Thanks

 

Harley says you can use their syn 3 in all three holes. As well as Amsoil, and mobil1 v-twin. Amsoil and mobil 1 v-twin say their oil has the gl-1 rating, but Harleys doesn't. I haven't been able to find a motorcycle specific oil that has an official API rating on the bottle. The claim their oils meet or exceeds the API standard, but don't want to pay for the symbols use. Gl-1 is the lowest rating for a gear oil you'll find, while most other gear oil is gl-5 rated. Lots of guys use synthetic gear oil that carries the gl-5 rating on the bottle without issues. I use mineral gl-5 rated gear oil in my '96, and it works fine in my 5 speeder.,,,

 

Check it out carefully before using. Mobile website says don't use their GL 5 in a tyranny that doesn't specify it. It has to do with corrosive effect on the yellow metals in the tyranny, whatever that means.

 

Yellow metals = brass/bronze syncro rings. Your HD doesn't have them.

I have a 5 speed running Spectro Platinum 6 speed oil, absolutly no issues and no noise. Butter.

Ken

 

Use it and you will never go back. Plus the "yellow metal" corrosion thing is from high sulphur gear oils in the 1960's & 70's. The new synthetics don't attack any metals.

 

Good to go. GL-1 is all that is required (which the oils meet), but Gl-5 won't hurt a thing.

 

That Spectro is a full synthetic gear oil rated at a GL-5. Isn't that a lot of overkill? I mean the a GL-5 gear oil is rated as the best, why would you need a synthetic formulation to go with it.
I use a mineral based GL-5 gear oil and when I drain it after 20,000 miles it comes out as red as the day I put it in.

 

The Spectro synthetic GL-5 could easily go 4-5 times longer than the mineral product.

It is also a 75w-140 where you mineral fluid does not have that wide of viscosity spred.

Ken