Most lubricants for manual gearboxes and differentials contain extreme pressure (EP) additives and antiwear additives to cope with the sliding action of hypoid bevel gears. Typical additives include dithiocarbamate derivatives and sulfur-treated organic compounds ("sulfurized hydrocarbons").
EP additives which contain phosphorus/sulfur compounds are corrosive to yellow metals such as the copper and/or brass used in bushings and synchronizers; the GL-1 class of gear oils does not contain any EP additives and thus finds use in applications which contain parts made of yellow metals.
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