TRANSMISSION LUBRICATION

The lubrication of transmission or drivetrain components can be quite complicated, with recommended oils and fluids for the gearbox, differential and in the case of all-wheel-drive vehicles, the transfer box too. The classic Mini’s A-series engine, gearbox and differential for instance share the same 20W-50 mineral oil, whereas most FWD cars have separate oil for the engine and the gearbox/differential, while rear-wheel drive cars use separate oil for the engine, the gearbox and the differential. Hopefully the following pages will help you understand why there are so many differences, and which transmission oil is the best for you.

Grades and Abbreviations

Just like engine oil which we covered in the July issue, gear oil is graded according to its viscosity rating. The Society of Automotive Engineers (SAE) has developed a grading system for the viscosity of monograde and multigrade oils that can be applied to gear oils. SAE grades for gear oil start at 65, and the grading system was last revised in February 2019 (known as SAE J306). The higher the value, the greater the viscosity (in other words, the thicker the oil). Where a gear oil has two numbers such as 75W-90, the first number is its