What Oil In The Gearbox

[geeves]

One big word of warning about 75/80 gearbox oil. First and least important gear oils rate viscosity differently to engine oil and 75/80 isnt much different to 30/40 engine oil. More importantly there are 2 75/80 gear oils. One is designed for gearboxes and this is good oil. The other is labeled as hypoid or extreme pressure. This contains a hypoid additive which is great in the diff but it breaks down if it gets hot turning into acid. Also it corrodes brass and syncro rings are made of brass. Do not use hypoid oils in gearboxes except if specified in the handbook. This is not the case with light Isuzu diesels.