Transfer Case: Description: General

The NV225 Transfer Box is a full time, permanent four wheel drive, torque splitting transmission with equal torque distribution to the front and rear propeller shafts. The transfer box has the following features:

Permanent four wheel drive with 50/50 torque split.
Two speed, fully synchronized SHIFT ON THE MOVE system with electronic control and operation.
High range direct drive and low range via epicyclic gearset.
Torsen® Type B torque sensing and torque biasing center differential.
Self lubricating oil pump system.

The transfer box is located under the vehicle in a subframe, behind the transmission. The units used on both the Td6 and V8 variants are identical, with the exception of the large mounting bush. The transfer box is manufactured by New Venture Gear in Roitzsch, Germany.

The transfer box receives an input from the transmission output shaft which is passed through the unit to two outputs for the front and rear propeller shafts.

The transfer box provides full time four wheel drive via a 50:50 torque sensing Torsen® differential. The unit design allows "shift on the move" from high to low range and visa versa. A planetary gearset with helical planetary pinion gears provides low range operation. When in low range, the planetary gearset provides a ratio of 2.69:1 which gives the vehicle an extremely low, low range crawl speed. High range is a direct drive from the transmission output shaft and provides a 1:1 ratio.

The transfer box has electronic control, via a PWM actuator (DC motor), on the shift from high to low range. The actuator is controlled by a transfer box ECU, which is located behind the battery in the engine compartment.

The major components of the transfer box are; the front casing assembly, the rear casing assembly, the planetary gearset, the Torsen® differential, the fork and rail assembly and the actuator assembly.

The front and rear casing assemblies are manufactured from cast aluminum. Fins are cast into the front casing to aid heat dissipation. Both casing assemblies are bolted together and provide the bearing locations for the main shaft, the Torsen® differential and the planetary gearset. The rear casing provides the attachment location for the actuator assembly.

An oil pump assembly is located in the rear casing and is driven by a splined coupling on the main shaft. The pump has an oil tube to the bottom of the two casings with a filter screen to collect particulate matter. A magnet is located below the filter screen to collect any metallic particulate matter. The oil pump provides a pressurized supply to a drilling in the center of the main shaft. Cross-drillings in the main shaft provide lubrication for the bearings and rotary components.

On Td6 engine models, a mass damper is fitted to the front casing assembly. The damper is located next to the front output flange and secured to the casing with bolts. See Fig 1. The damper absorbs vibration and resonance inherent with diesel engines, reducing passenger compartment noise and vibration.

Fig 1: Locating Mass Damper (Td6 Models Only)

Courtesy of LAND ROVER NORTH AMERICA, INC.

The front casing assembly houses a mounting bush which differs in its material between engine variants. The bushes are identified by a color code; red is for V8 engine models and blue is for Td6 engine models. The construction of the bushes is visually identical. The material from which the bushes are constructed differs to absorb the differing vibrational frequencies between the engine variants.

Drive is passed from the input shaft and via the Torsen® differential to the mainshaft and the drive sprocket assembly. The mainshaft rotates and passes the rotational motion to the rear propshaft. The drive sprocket assembly rotates and passes this rotation, via the chain, to the front propshaft. The drive sprocket carries a 3/8" pitch drive chain which drives a sprocket which is integral with the front output shaft. Because both sprockets are the same, with the same number of drive teeth, the rotational motion of the drive sprocket is identical to that of the front output shaft sprocket.

The 50:50 torque output ratio is produced from the Torsen® differential unit. This unit can drive the output to the main shaft and the drive sprocket assembly at a 50:50 ratio during normal driving conditions.

The transfer box requires a unique oil developed with NVG and Burmah-Castrol specifically for the Land Rover transfer box. The oil is a fully synthetic with the following specification: BOT 26 FMB 1 75W-90. The oil contains unique additives which enhance the transfer box operation. No other oil must be used in the transfer box.

Should the transfer box require repair, the only serviceable items are the input and two output shaft seals, the drain and filler plugs, the actuator and gearbox assembly and the breather tube. Any repairs beyond the items listed requires a replacement transfer box.

A filler/level plug is provided to ensure that the correct oil level is achieved after a service repair has been carried out. The level must be checked and adjusted with the transmission fully assembled and the vehicle on level ground. The transfer box contains 0.996 liters (1.1 quarts) of oil. The transfer box is a fill for life unit and no level check is required at service unless a leak is present.