The oil originally recommended for the Land Rover LT77 manual gearbox (a 5-speed gearbox fitted to the Classic Range Rover, Defender and Discovery up to 1994) is Dexron II D or Dexron III automatic transmission fluid (ATF).

The LT77 gearbox is fitted with a highly sensitive internal oil pump. Using standard manual gearbox oil (such as 75W90 or 80W90) is strongly discouraged, as its excessively high viscosity would quickly damage the pump and make it impossible to change gears when the gearbox is cold.

The two options recommended by specialists:

1. The original choice: ATF Dexron III. This is the standard fluid which provides excellent lubrication for the pump and facilitates gear changes when the gearbox is cold. Specialists in refurbishing these gearboxes always recommend using ATF Dexron 2 or 3.
2. The modern alternative: MTF 94-type oils or dedicated synthetic fluids Although MTF 94 oil was introduced later by Land Rover for the R380 gearbox, many users and mechanics use it in the LT77. It offers better protection for hot gears during intense exertion (for example, when pulling a load or on the motorway) compared to ATF, which tends to thin out under the effect of heat. High-end alternatives such as Redline MTL also provide a high level of comfort.

Summary of transmission fluids (LT77 + transfer box):
LT77 gearbox: Dexron III ATF (or MTF 94) ~2.2 to 2.4 litres
LT230 transfer box: EP90 GL4 or 80W90 GL4 (Note: Avoid pure GL5, as it corrodes bronze) ~2.5 to 2.8 litres

To help you choose, bear in mind that if your LT77 gearbox is a little stiff when cold (particularly when shifting into second gear), Dexron ATF remains the smoothest option for making gear changes more fluid. If you use your Land Rover for long journeys with a heavy load or for towing, MTF 94 offers better oil film stability at high temperatures.