Abstract: In a motor vehicle, especially a heavy duty motor vehicle, having a transmission equipped with at least one cone-type synchronizer and an axle or differential gearing, the same lubricant is used for both such mechanisms. The lubricant has a viscosity grade level of from SAE 75W90 to SAE 85W140 and comprises base oil containing at least (i) Mannich base ashless dispersant; (ii) metal-free, sulphur-containing antiwear and/or extreme pressure agent; (iii) metal-free, phosphorus-containing and nitrogen-containing antiwear and/or extreme pressure agent; and (iv) overbased alkali or alkaline earth metal carboxylate, sulphonate or sulphurized phenate having a TBN of at least 145. The lubricant contains at most, if any, 100 ppm of metal as one or more metal-containing additive components other than (iv).

Abstract: The frictional properties of gear oils are improved by including at least one overbased alkali or alkaline earth metal carboxylate, sulphonate or sulphurized phenate having a TBN of at least 200 in a gear oil which comprises: oil of lubricating viscosity at least 80% by volume of which is mineral oil, synthetic ester oil or a mixture thereof; Mannich base ashless dispersant; metal-free, sulphur-containing antiwear and/or extreme pressure agent; and metal-free, phosphorus-containing and nitrogen-containing antiwear and/or extreme pressure agent. The resultant gear oils exhibit excellent performance when used in synchromesh-based transmissions.