Gear fluids

A method of improving the solubility of one or more friction modifier components in a friction modifier additive package comprising blending at least one alky phosphonic acid diester of the formula:

• with at least one alkyl phosphonic acid monoester of the formula:
• and with at least one amine salt of a partial ester of phosphoric acid represented by the formula
• wherein R1 and R4 are selected from a hydrocarbyl group containing from about 8 to about 24 carbon atoms;
• R2, R3 and R5 are independently selected from hydrogen and a hydrocarbyl group containing from about 1 to about 8 carbon atoms;
• and each of R6 and R8 is, independently, a hydrocarbyl group, and R7 is hydrogen or a hydrocarbyl group, wherein the foregoing components are blended in an amount of a base oil component sufficient to solubilize substantially all of the alkyl phosphonic acid monoester and diester, and wherein the ratio of the diester to the monoester of the alkyl phosphonic acids ranges from about 3 to about 5.5.

A method for improving the friction performance of a gear fluid comprising providing an additive package to a gear fluid, the additive package comprising a base oil component and a friction modifier mixture including:

• (i) at least one alkyl phosphonic acid diester of the formula:
• wherein R1 is a hydrocarbyl group containing from about 8 to about 24 carbon atoms, R2 and R3 are independently selected from a hydrocarbyl group containing from about 1 to about 8 carbon atoms;
• (ii) at least one alkyl phosphonic acid monoester of the formula
• wherein R4 is a hydrocarbyl group containing from about 8 to about 24 carbon atoms, R5 is selected from hydrogen and a hydrocarbyl group containing from about 1 to about 8 carbon atoms;
• and
• (iii) at least one amine salt of a partial ester of phosphoric acid represented by the formula
• wherein each of R6 and R8 is, independently, a hydrocarbyl group, and R7 is hydrogen or a hydrocarbyl group, and wherein the ratio of (i) to (ii) ranges from about 3 to about 5.5.