HOW IT ALL WORKS
THE TRANSFER box is the heart of the beam axle Land Rovers’ four-wheel drive system. It transfers the drive (from the gearbox) across and out at the front and rear of the transfer casing to drive the propshafts to the front and rear axles. Unlike the earlier transfer boxes on Series Land Rovers which had rear-wheel drive and manually selectable front drive, the LT230 provides permanent drive to both axles, thanks to its integral differential.
Centre diff A so-called centre differential inside the transfer box allows the relative speeds of the front and rear propshafts to vary, thus allowing the front axle to rotate faster than the rear, which it needs to do when turning a corner. The downside of the centre differential is that, if a wheel on one axle loses grip and spins, all the transmission torque will be sent to that wheel (it takes the path of least resistance). So, the axle that does have grip doesn’t receive any drive, and the vehicle is stuck. That’s where the transfer box’s centre diff lock comes in. Operated by the short lever in the cab, it locks the differential so that both propshafts rotate together, and are no longer independent of each other. So, if the rear axle now loses grip, the front axle will still be driven, keeping the vehicle moving (usually). As diff lock lever is used, its linkage operates a selector fork, which moves a dog clutch on the centre diff’s shaft to engage with a gear on the front output shaft, locking both drives together.
Centre diff lock is intended for off-road use on loose ground where the tyres will slip a little to accommodate the difference in front/rear axle speeds when cornering. It should not be engaged on the road, or other firm surface, because the tyres are unable to slip, resulting in high stress in the driveline (otherwise known as transmission wind-up).
Hi and low ratios As we know, the transfer box also provides the choice of high or low ratio gearing, selected by fore and aft motion of the same lever as is used for difflock. Diff lock works in either ratio, and also works with electronic traction control (if fitted).
The transfer box is, of course, driven by the gearbox mainshaft which protrudes into the transfer box casing to drive the transfer gear. This, in turn, drives the intermediate gear, which continually drives the high and low ratio output gears on the right-hand side of the transfer box. These ratio gears rotate on a splined hub on the centre diff’s rear shaft. When the ratio lever in the cab is moved, high or low ratio is engaged by a selector fork as it locks the chosen gear to the centre diff’s rear shaft.