Gear and transmission lubricant compositions of improved sludge-dispersibility, fluids comprising the same

A gear or transmission lubricant composition, which comprises:

• a major portion of mineral base oil, having a viscosity of 1.about.50 cSt. at 100.degree. C. and having a viscosity index of at least 60;
• containing, based on the weight of the composition,
• 0.05-3% of (A) at least one phosphorous-containing metal-free organic compound, selected from the group consisting of compounds represented by any of the following formulae (1), (2), (3) and (4):
• O.dbd.P(OR).sub.p (OH).sub.3-p ( 1)
• O.dbd.P(OR).sub.q (OH).sub.3-p. NH.sub.r R'.sub.3-r ( 2)
• P(OR).sub.q (OH).sub.3-p ( 3)
• P(OR).sub.q (OH).sub.3-q. NH.sub.r R'.sub.3-r ( 4)
• wherein p is an integer of 1.about.3;
• q and r are independently integers of 1 or 2;
• R is selected from the group consisting of saturated or unsaturated aliphatic hydrocarbyl groups containing at least 4 carbon atoms and alkyl-substituted aryl groups;
• R' is selected from the group consisting of saturated or unsaturated aliphatic hydrocarbyl groups containing at least 4 carbon atoms;
• and 2-25% of (B) at least one oil-soluble copolymer containing 92.about.99% by weight of monomer units of (a) alkyl acrylate or methacrylate and 1.about.8% by weight of monomer units of (b) N,N-dialkylaminoalkyl acrylate or N,N-dialkylaminoalkyl methacrylate.