FIRST - THIS IS NOT AN OIL DEBATE THREAD
If you want to use Motor Oil, ATF, or cat **** in your gearbox knock yourself out.
If you have a Big Twin, this isn't really applicable to you.

There has been much discussion and debate in the past few years over the use of GL5 Gear Oil in the Sportster Primary/Tranny. This debate centers around warnings that GL5 Gear Oil is corrosive and that it can damage what are known a "yellow" metal parts. Unlike the Big Twins, our Sportsters have a shared primary/tranny and that means that the stator (copper) and clutch spring plate (brass rivets) can be damaged if a corrosive lubricant is used in our application.

The question over the safety of GL5 has been hard to nail down because many of the manufactures will give out conflicting information depending on who you talk to, even within the same company.

WHY is this such a hard question for the oil companies to answer with factual data and WHY is it so hard to find a real answer to the question? The answer is really pretty simple.

Anyone who has spent time studying oil knows about the myriad of various ratings that are applicable for any particular lubricant, from JASO, CF, MIL, etc. The number of different tests that can be done on oil run well into the hundreds, so oil testing by the manufacturer is typically limited to those tests that are applicable to the oils intended use.

So why is it so difficult to get answers to the GL5 corrosive question? It's rather quite simple. Because GL5 is made for use in hypoid gearboxes which by nature don't contain yellow metals, so most manufactures don't perform the standard ASTM D-130 corrosive test on GL5 lubricants.

After quite a bit of digging, it turns out that spAmsoil has actually done ASTM D-130 testing on a number of common/popular GL-5 Gear Oils.

ASTM D-130 ratings fall on a scale going from 1A (least corrosive) to 4C (most corrosive) From a corrosive standpoint, an oil with a 1A or 1B rating is considered safe.

ASTM D-130 ASTM D-4048 FTM-5309 "Detection of Copper Corrosion from Petroleum Products by the Copper Strip Tarnish Test"
A variety of hydrocarbon products including oils, hydraulic fluids, fuel, solvents, etc., can be tested for corrosivity to copper by use of this test. It is limited to products with Ried Vapor pressure no greater than 18 psi (124 kPa). A polished copper strip is immersed in the fluid and heated for a specified time and temperature after which the corrosion is rated by visual comparison to the ASTM Copper Strip Corrosion Standards. The most typical test run is for 24 hours @ 100°C. However, time and temperature can vary according to product type and specification. Results are reported as a number followed by a letter according to the following scheme:

1a slight tarnish a light orange, almost the same as a freshly polished strip
1b dark orange
2a moderate tarnish a claret red
2b lavender
2c multi colored with lavender blue or silver, or both, overlaid on claret red
2d silvery
2e brassy or gold
3a dark tarnish a magenta overcast on brassy strip
3b multi colored with red and green showing (peacock), but no gray
4a corrosion a transparent black, dark gray or brown with peacock green barley showing
4b graphite or lusterless black
4c glossy or jet black

(The ASTM Copper Strip Corrosion Standard is a color reproduction of strips which have the above description.)

The following is the latest product list I could find that has undergone ASTM D-130 testing.

SAFE GL-5 Oils
Amsoil M/T Fluid MTF..5W-30.............. 1A Light Orange
Red Line MT-90.......75W-90 GL4......... 1A Light Orange
Amsoil Long Life FGR 75W-90 GL5......... 1B Dark Orange
Amsoil Severe Gr SVG 75W-90 GL5....... 1B Dark Orange
Amsoil MT & Gear MTG 75W-90 GL4...... 1B Dark Orange
Mobil 1 Synthetic....75W-90 GL5......... 1B Dark Orange
Castrol Hypoy C......80W-90 GL5......... 1B Dark Orange
Castrol SYNTEC.......75W-90 GL5........ 1B Dark Orange
Citgo Citgear Std XD 75W-90 GL4........ 1B Dark Orange
GM Synthetic Axle....75W-90 GL5........ 1B Dark Orange
Pennzoil Gearplus....80W-90 GL5.......... 1B Dark Orange
Pennzoil Synthetic...75W-90 GL5......... 1B Dark Orange
Red Line NS Gear Oil 75W-90 GL5......... 1B Dark Orange
Red Line 75W90 GL-5..75W-90 GL5....... 1B Dark Orange
Torco SGO Syn G LS....75W-90 GL5...... 1B Dark Orange
Valvoline High Perf..80W-90 GL5........... 1B Dark Orange
Valvoline SynPower...75W-90 GL5......... 1B Dark Orange

MARGINAL GL-5 Oils
Delo Gear Lubric ESI 80W-90 GL5.......... 2A Claret Red
Delo Trans Fluid ESI 50W..................... 2A Claret Red

UNSAFE GL-5 Oils
Royal Purple MaxGear 75W-90 GL5......... 4A Trans Black
Mopar Syn LS additive..75W-90 GL5....... 4A Trans Black
Lucas 75/90 Synthetic75W-90 GL5......... 4B Graphite Blk


More information on Amsoil's Gear Oil Testing can be found in this document.
www.oilteksolutions.com/GearLubeWhitePaper.pdf

 

Wow! Thanks for the info cHarley!

 

Thank you for this info.
Barry In MO.

 

Good read. I'm surprised this hasn't discovered by anyone before considering it's from 2007. The science doesn't lie.

 

Wow, this is good stuff. It sure clears up questions about some of the off the shelf gl-5 oils that are available from auto parts stores. Looks like all your previous recommendations for Mobil-1 75w-90 Gear Oil was in fact a safe choice.

Thanks Charley

 

Thank you for providing a moment of clarity in all the fog! This will definitely put my fears to rest since I've been following this GL-5/yellow metals issue for a while.

Plus, I recently put M1 75W-90 in my primary and started to have second thoughts.

John

 

Great info. So it boils down to WHATEVER you want to use if it doesnt meet ASTM D-130 standards for 1A or 1B, or if the manufacture hasnt tested it for that or wont provide it............DONT USE IT

 

Here, found a picture of some samples:




And a pretty exhaustive test of some gear oils (copper corrosion test in part 2):

http://www.smokinvette.com/corvette/...-lubes-part-1/
http://www.smokinvette.com/corvette/...-lubes-part-2/

 

Great Info cHarley!

Nice to finally have some test info to compare.

 

Correct.
What I should have clarified better in the OP, is that the point of this thread is not to start another debate over which oil is best, that debate will never end. But instead, to provide information on "Off the Shelf" Gear Oil choices that are yellow metal safe.

Amsoil and Redline have Gear Oil products that have long been known to be yellow metal safe, but neither are typically readily available at your local auto parts store or Wally World and both are expensive and rather costly to ship. This list of provides us with several good choices that can be found at almost any local auto parts store.

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