Reconditioning a transfer gearbox gives opportunities for some interesting and useful modifications, as well as the driving benefits of new bearings and shims, etc.
If you have tuned or modified your engine and gearbox, or if you use your Defender in unusual ways, or both, you might want to change the ratio of the transfer gearbox. If your engine has plenty of torque, and you often drive at quite high speeds, you might want to change for a longer ratio. TD5 Defenders had 1.4 : 1 gears as standard, but when those engines were tuned up, many owners found they preferred to fit 1.2 : 1 gears so as to reduce engine rpm and provide more relaxed cruising performance on motorways. Customers who tow heavy trailers, or who fit larger wheels and tyres, sometimes want shorter ratios.
Recent standard Land Rover ratios include :
Puma 2.2 or 2.4 engines, all : 1.21 : 1
TD5 90 and 110 : 1.41 : 1
TD5 130 : 1.67 : 1
Alternative ratios currently available :
1.00 : 1, 1.10 : 1, 1.22 : 1, 1.30 : 1, 1.41 : 1, 1.67 : 1
If your car currently has 1.21 : 1 ratio and you want to reduce engine rpm on the motorway, a 1.1 : 1 unit will reduce the rpm by 9%. So if, at a certain speed, the engine was doing 2,700 rpm, after the ratio change it will be doing 2455 rpm.
Limited slip differential.
Another special feature you can add is a limited slip centre differential. In normal use, when cornering, the wheels of the front axle travel at slightly different speed to those of the rear. To allow for this there is a differential in the transfer gearbox. If you are travelling at speed on bumpy terrain and the wheels leave the ground, or if you are driving on snow, ice, or mud, then some wheels might start to spin faster than the others. You can use the differential lock, but that can reduce steering effectiveness, and only feels right when the surface is poor over a good distance. The limited slip centre diff limits wheel spin and allows good handling and steering. If you really need to lock the centre diff, you still can, but when unlocked the limited slip unit greatly improves traction and limits wheel spin.
Transfer Box Upgrade
Basic transfer gearbox reconditioning, fitted to vehicle –
Recondition with changed ratio, fitted –
Recondition and add limited slip differential, fitted –
Recondition, change ratio, and add limited slip diff., fitted –