96 Fitting a higher ratio transfer box

Higher gearing in a Defender is possible by fitting a Discovery transfer gearbox. Trevor Cuthbert describes how

Achieve higher gearing in your Defender with this how-to guide

DEFENDER’S overall drivetrain gearing is optimised by the manufacturer as the best compromise for the tyre-wheel size, the engine power and torque characteristics, and the general work application the vehicle will be put to, such as towing duties and rated towing capacity.

Earliest models of the coil sprung utility (Ninety and One Ten) had lower powered engines and therefore the final gearing – dictated largely by the transfer gearbox – had to be lower. These early vehicles were fitted with a 1.667:1 ratio transfer gearbox, meaning the input shaft from the gearbox rotated 1.667 times for each single turn of the output flanges to the propshafts.

On the more powerful 200Tdi, 300Tdi and Td5 Defenders, the transfer gearbox ratio was higher at 1.41:1 (input gear turns 1.41 times for each turn of the output flanges). This is the best transfer gearbox ratio to have for a Defender that does extensive heavy towing on standard tyres sizes and with factory spec engine power.

The Land Rover Discovery 200Tdi, 300Tdi and Td5 models were fitted with a higher transfer box gear ratio of 1.222:1, which imparted higher cruising speeds into these more passenger-orientated vehicles. This 1.222 ratio LT230 transfer box is a popular upgrade for Defender models and is very successful, unless the owner is running very tall over-size tyres, or does lots of towing close to the 3.5 tonne rated limit. One of my friends recently fitted a 1.222 transfer gearbox to his Defender 90 Td5 pick up and says it has transformed his Land Rover.

The owner of the Td5 90 station wagon here does no towing at all, and therefore had no hesitation in asking for a 1.222 upgrade to his Defender during the re-chassis work, which is an ideal time to swap the transfer box.

Where low ratio is best

The 1.667:1 ratio transfer box was not only fitted to the early low-powered utility models; I own a 1997 Defender station wagon that was factory fitted with the very powerful BMW 2.8i straight-six petrol engine. The 1.667 transfer gearbox was selected for this model, as the engine is designed to be high revving and performs best at the higher rev ranges – lower gearing was required as a consequence of getting the best out of the engine.