Lubricant composition

A helicopter transmission lubricant composition formed by combining components comprising:

• a) a base component comprising one or more synthetic base stocks, which base component has a viscosity in the range of from 8.5 to 9.5 cSt at 100.degree. C.;
• b) at least one antioxidant selected from aromatic amines and hindered phenolics;
• c) at least one neutral organic phosphate of the formula (R.sup.1 O).sub.3 PO where R.sup.1 is a tolyl, phenyl, xylyl, alkyl or cycloalkyl group, the alkyl or cycloalkyl group having up to 10 carbon atoms;
• d) at least one saturated and/or unsaturated dicarboxylic acid of the general formula ##STR4## wherein x+y+z is an integer in the range from 2 to 22 inclusive and where at least one of the groups R.sub.1 to R.sub.5 is a carboxylic acid group and the remaining groups R.sub.1 to R.sub.5 are selected from alkyl, hydroxy, nitro, amino, carboxyl, hydrogen or alkyl derivatives thereof, where alkyl is a short chain of up to 5 carbon atoms;
• and/or a dicarboxylic acid of one of the three formulae ##STR5## wherein R.sub.1 ' is --COOH, alkyl, hydroxy, nitro, amino, hydrogen or alkyl derivatives thereof;
• R.sub.2 ' is --COOH;
• and n is an integer from 1 to 4 inclusive when R.sub.1 ' is --COOH or an integer from 2 to 4 inclusive when R.sub.1 ' is not --COOH;
• e) at least one straight and/or branched chain saturated or unsaturated monocarboxylic acid which is optionally sulphurised in an amount which may be up to 35% by weight;
• and/or an ester of such an acid;
• and
• f) at least one triazole of the formula:
• ##STR6## where R.sub.1 " is --COOH or alkyl derivatives thereof, or short chain alkyl of up to 5 carbon atoms;
• n is zero or an integer between 1 and 3 inclusive;
• and R.sub.2 " is hydrogen, morphilino, alkyl, amido, amino, hydroxy or alkyl or aryl substituted derivatives thereof;
• or a triazole selected from 1,2,4 triazole, 1,2,3 triazole, 5-anilo-1,2,3, 4-thiatriazole, 3-amino-1,2,4 triazole, 1-H-benzotriazole-1-yl-methylisocyanide, methylene-bis-benzotriazole and naphthotriazole;
• and
• g) an extreme pressure additive component comprised of a mixture of an amine phosphate in an amount of from 0.2 to 0.6% by weight of the lubricant composition and a phosphorothionate in an amount of from 0.5 to 1.5% by weight of the lubricant composition, said components being combined in amounts such that the composition achieves a score of at least 200% in the Ryder gear test at 100.degree. C.