Originally Posted by mker
Copy from Wikipedia
" 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").[2]
That blurb from Wiki was not from a formulator who formulates modern gear lubricants and Wiki is behind the times when it comes to knowing what chemistry is in modern gear lubes.
Originally Posted by mker
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.
Had you been reading informative posts here on BITOG you would know that this is a perpetuated myth by misinformed individuals. Buffering compounds such as metal and corrosion inhibitors keep any S-P compounds from attacking copper alloys. Besides, Modern differential gear lubes use more multi-functional Phosphorus compounds than they do sulfurized ester compounds. Potassium Borates are also used as secondary (cold temp) EP additive which also helps to inhibit any copper alloy corrosion. BTW, "yellow metals" are copper alloys.
Originally Posted by mker
GL-5 is not necessarily backward-compatible in synchro-mesh transmissions which are designed for a GL-4 oil: GL-5 has a lower coefficient of friction due to the higher concentration of EP additives over GL-4, and thus synchros can not engage as effectively.
"
Who said anything about backward compatibility? Not I. Once again, your information is incorrect so quit throwing out Strawmen fallacies and committing fallacies of Presumption. GL-5 DOES NOT have a lower coefficient of friction than do properly formulated MTF lubes.
GL-5 differential fluids contain Extreme Pressure additives for highly loaded pinion to ring gears. MTL lubricants contain Anti-Wear additives because the gear sets are not as highly loaded as hypoid differentials and contain friction modifiers for synchronizer assemblies. and differential lubes are higher in viscosity than their MTL counterparts of the same grade.
MTL's with GL-4 ratings contain specific AW and FM additives, and base oil viscosities suited to MT's.
GL-5/MT1 lubricants contain higher viscosity base oils and EP additives for high loads.
Whether it be a GL-5 differential fluid or MTF's, they all contain buffering compounds in the form of metal deactivators and corrosion inhibitors, and contain additives packages suited for their respective application.
Rather than endlessly arguing, You really need to read these white papers and educate yourself before you make any more incorrect and presumptve statements::
https://www.bobistheoilguy.com/foru...bology-and-lubrication-part-i#Post729255
https://www.bobistheoilguy.com/foru...bology-and-lubrication-part-i#Post729255
https://www.bobistheoilguy.com/foru...nual-transmission-lubricants#Post1231182