quote:
As I understand it, GL-4 lubes contain 1/2 the zinc and phosphorus amounts that GL-5 lubes have. Phosphorus apparently attacks yellow metals, and the synchros need a certain amount of traction for proper function.
The Zinc-Sulfur-Phosphorus package in GL4 lubes is 1/2 to 2/3 the level of the GL5 lubes.
The difference in add levels is due to the fact that manual transmissions don't need as high a level of EP adds for the spur gearing, whereas hypoid differentials need extra EP because of their high loads and extensive shearing actions.
Most gear lubes today use the "non-reactive" sulfur-phosphate packages.
By "non-reactive," we mean that the sulfur is not just 'elemental' sulfur dissolved in oil, which would react with the metal to stain and corrode it.
Rather, the new S-P add packages are esterified (incorporated in fats) S-P's. These only react under pressure/heat of shearing and loads to form FeP and FeS EP surfaces films to prevent galling and wear. TBN boosters (TAN reducers), antioxidants, metal deactivators, and rust inhibitors are also incorporated to prevent acid buildup and to protect from rust.
The new ester packages do not stain or corrode copper alloy metals such as brass or bronze.
Special Friction Modifiers insure proper engagement of the synchros.
[ March 13, 2004, 12:51 PM: Message edited by: MolaKule ]