Why GL-1 is hard to find.
From:
API GL-5: Clearing up the Confusion - Automotive Gear Oil Additives - Driveline Additives - The Lubrizol Corporation
API Categories GL-1, GL-2, GL-3 and GL-6 were declared inactive by SAE Technical Committee 3 in 1995, even though oils may be marketed with these designations. Similarly, ASTM does not plan to maintain the performance tests associated with these categories, as in a number of cases these tests can no longer be run because parts or test installations are not available.
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GL-5 often has sulpher compounds added for EP service, but not always. You may have to get the specs of the oil and check the corrosion test results.
From:
Gear Oil Questions Answered
"Q: I heard that EP additives are corrosive to yellow metals such as brass and bronze. Is this true?
A: In some circumstances, this can by true. Certain types of EP additives are designed to react with metal surfaces under elevated temperatures to protect them under boundary lubrication conditions. These types of additives are often referred to as “chemically active”, and at elevated temperatures (greater than 140 to 150 F), they can indeed start to react with yellow metals. For this reason, apply caution when selecting gear oils for worm drives; the ring gear is often a yellow metal alloy.
A good way to check to see if an oil is “chemically active” is to look at the specification sheet provided by the lubricant manufacturer. On the sheet, you will typically see a test referred to as “copper strip corrosion” (ASTM D130). This tests how chemically reactive an oil is to copper and copper-containing alloys. For gear oils, a 1a rating is typically a good indicator that the oil is chemically inert, while higher ratings (such as 1b or 2a) might indicate possible problems when used in certain gearing at elevated operating temperatures. Often, a lubricant manufacturer will specifically state “this oil should not be used in gearboxes containing yellow metals”; other times, the manufacturer will simply state that the oil is appropriate for “steel-on-steel” applications – the implication being that they should not be used in situations where the ring gear is brass or bronze."
Bruce
