Selecting the proper gear oil for your manual transmission is just as important as choosing the correct motor oil or brake fluid and shouldn’t be overlooked. Various gear oils react differently to gearboxes, so choosing the wrong gear oil can lead to your gearbox being notchy, or worse, a reaction between the gear oil and gearbox components which can damage your transmission or shorten its lifetime.
Gear oil is a lubricant made specifically for manual transmissions, with a higher viscosity than regular engine oils to better protect the gears. This high viscosity ensures the necessary transfer of gear oil throughout the transmission, as most gearboxes rely on splash lubrication and do not have pumps for oil delivery.
Fully synthetic gear oils are used in many vehicles, and have a greater resistance to shear compared to mineral oils. Also, many gear oils contain additives including sulphur-bearing anti-wear additives to cope with the high sliding friction inherent in the helical gears used in modern vehicles, hence the strong sulphur smell people often talk about.
Gear oils are classified by the American Petroleum Institute (API) via GL ratings. It is important to check the oil with your vehicle manufacturer’s specifications to ensure it does not contain any incompatible additives which may react with yellow metal components, such as the brass or bronze used in bushings and synchromesh.
The synchromesh in manual gearboxes relies on friction to match the gear speeds when changing gears. Oil that is too thick or the presence of certain additives may impact on the friction required to match the gear speeds, hence a notchy-feeling gearbox, or one which is more difficult to change gears.
Motul’s range of synthetic, Technosynthese® and mineral gear oils are suitable for a range of gearboxes and applications, from regular driving to racing. Their selection of API GL-4 and GL-5 gear oils feature:
• Exceptional shear stability with 0% shear loss, enabling the gear oil to retain its viscosity during operation;
• Very high lubricating power, reducing friction and wear;
• Outstanding performance at high temperatures, providing excellent oil film resistance and a reduction in transmission noise;
• Optimum low temperature performance characteristics to allow easier gear shifting when the gearbox is cold;
• Suitability with all seal types as well as with yellow metals;
• Anti-corrosion and anti-foaming formulation to protect your transmission.
Motul also offers NISMO Competition Oil recommended by Nissan and NISMO and designed especially for the GT-R R35, while also offering all of the advantages regular Motul gear oils are renowned for.
For more information on the full range of Motul Gear Oils visit: https://www.motul.com/au/en/products/oils-lubricants?f%5Brange%5D=25