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Transmission Fluids 101

We Are Learning with the Help of the Spectro Gang

By Wrench with photos from Bob T. and the Spectro Union

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Bandit just built this funky swap meet Panhead. It drips oil everywhere.
Bandit just built this funky swap meet Panhead. It drips oil everywhere.

I’ve been sorta confused by the markings on transmission oil bottles. Then someone published another puzzling report. We can run 50/20 engine oil in our transmissions and primary cases.

I needed some clarity, so I reached out to the masters of Spectro Oils. Joe Russo, National Sales manager kicked off the research, John Dunne, the master engineer answered my questions and Luke Calzone, the director of marketing supplied images and info.

Let’s take a look at what we found:

While engine oils and trans fluids can use some of the same base stocks, both petroleum and synthetic, they have marked differences in their additive technology. Engine oils contain detergents and disperents to help with cleaning due to the combustion process in engines as well as antiwear technology.

Gear oils and transmission oils do not need the Detergent and dispersant additives because they do not deal with combustion byproducts.

In straight cut gears you need antioxidants and antiwear protection. In transmissions or gears where there is heavy whipping, the additives of choice are Sulfur and phosphourous, used in GL-4,GL-5 Hypoids, they offer excellent protection and keep units clean!

A 75W90 gear oil viscosity is about a 10W50 in engine oil viscosity range, so if you have a 75W140 gear oil, it is quite high in viscosity and thus good in heat and providing film strength!

A Hypoid gear is a bevel wheel with teeth engaging with a spiral pinion mounted at right angles to a wheel axis and is used to connect intersecting shafts in vehicle transmissions and other mechanisms.

A Hypoid oil means it contains EP agents same as a GL-5 fluid sulfur and phosphorous, protects where there is a heavy whipping, load on the surfaces.

A GL-1 fluid has anti-wear and anti oxidation components and is used where straight cut gears are operating.

—John Dunne

Heavy Duty Platinum Full Synthetic 6-Speed Transmission Lubricant
This unique lubricant was developed for Harley owners who were unhappy about their noisy 6-speed transmissions.

It provides smoother shifting, reduces fifth gear whine and eliminates clunks. Spectro’s proprietary formula uses G4 Technology, special additives that provide additional anti-wear protection, higher film strength between the gears, and reduces drag while extending gear life.

High loads and extreme heat do not affect the oil, so it performs excellently when pushed hard and long. A.P.I. GL-5 rated. Dyed red. Exceeds all known OEM and Harley Davidson warranty requirements.


Heavy Duty Platinum Gear Oil
This is the top of the line, a full synthetic, PAO lubricant formulated specifically to run in Harley Big-Twin transmissions. We combine the leading synthetic PAO base oils with the most advanced additive package available today, to delivers maximum performance right through high loads and extreme heat.

Heavy Duty Platinum reduces drag, friction loss, wear. It also and extends gear life and provides exceptional temperature stability for easier, smoother shifting. A.P.I. GL-1 rated.

Dyed green. Exceeds all known OEM and Harley Davidson warranty requirements.


This is the ultimate gear oil for use in high performance transmissions. This fully synthetic formula has breakthrough additive technology and reduces power loss due to both drag and friction. Provides less wear on components, smoother shifting, reduces drag, friction losses, wear, and extends gear life. GL-1 rated.

75w90 L.75W901 12/1 liter bottles/case
75w140 L.75W1401 12/1 liter bottles/case

Heavy Duty Platinum Sportster Transmission Lube

Six-Speed synthetic technology is now available for the Harley Sportster/Buell. Spectro Heavy Duty Platinum Sportster Transmission Lube is a fully formulated synthetic transmission lubricant engineered to work in all applications where the same oil lubricates the clutch, primary, and transmission. A.P.I. GL-1 rated. Dyed green.

Exceeds all known OEM and Harley Davidson warranty requirements.

Heavy Duty Gear Guard
Spectro Heavy Duty Gear Oil is a premium quality gear lubricant formulated specifically to run in motorcycle transmissions to prevent rust, corrosion, oxidation and to combat foaming and gear pitting.

Formulated specifically for Big Twin Transmissions, it reduces drag, friction loss, wear, and extends gear life. A.P.I. GL-5 rated.

Dyed red. Exceeds all known OEM and Harley Davidson warranty requirements.

Heavy Duty Primary Chaincase Oil
This sheer stable petroleum is designed to withstand the punishment of high loads, and contains special polymers to provide exceptional clutch engagement and temperature stability.

Formulated specifically for Harley Sportster and Big Twin applications. Low drag, low friction loss SAE 85w viscosity eliminates clutch “drag” and slipping. Exceeds all known OEM and Harley Davidson® warranty requirements.



Spectro Hypoid is formulated with the highest density and highest V.I. petroleum base stocks available, then special EP additives are included to reduce pinion gear wear. This fine product is designed for the final drives and transmissions of all shaft drive motorcycles that do not have a wet clutch, including BMW®, MotoGuzzi®, older Harleys®, Big Twins. It reduces drag, friction losses, wear, and extends component life. API GL-5 rated.

80w90 L.HYP 12/1 quart bottles/case
80w90 W.80w90 5 gal pail
80w90 X.80w90 16 gal drum

Golden Motorcycle Gear Lubricant

This shear-stable petroleum transmission case lubricant is specially designed to withstand the punishment of second and third gear starts, so you can count on exceptional clutch engagement and temperature stability.

Recommended for all modern 2-cycle moto-cross gear/clutch cases where SAE 10w30 or SAE 10w40 SE/SF/SG or 80w lubricants are recommended.

Eliminates clutch “drag” and “slipping,” and meets all known motorcycle manufacturers’ warranty requirements. Not to be used for an engine lubricant.

80w L.GSCGL80 12/1 liter bottles/case
85w L.GSCGL85 12/1 liter bottles/case
80w X.GSCGL80 16 gal drum

That helped a lot and Spectro gives us lots of options. We’re learning.



ILC/Spectro Oils of America
993 federal rd
Brookfield,Ct 06804
Ph 203-775-1291
Fax 203-775-8720

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Reader Comments

I was hoping to get confirmation that GL-5 does or does not cause problems with bronze bushings in older Harley transmissions. I have heard it will cause flaking of the bronze, or something like that, and should be avoided. Thanks, Joe

joe savino
groton, CT
Wednesday, February 7, 2018
Editor Response Hey Joe, we spoke to John Dunne at Spectro:

Guys,Yes,some GL-5 fluids can be a problem with soft, old bronze or brass
components,however,the additive we use has a passivator in it that prevents
adverse reactions,



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