Land Rover LT230 Transfer Cases De-Mystified:

DESCRIPTION
• The LT230Q transfer gearbox is a permanent 4 wheel drive, two speed ratio reducing gearbox, incorporating high and low range outputs with mechanically lockable center differential (diff-lock). High/low range and diff-lock selection are made via a single lever located forward of the main gear lever.
• The transfer gearbox is mounted at the rear of the main gearbox, the mainshaft of which extends into the transfer casing. A transfer gear, supported on taper roller bearings and splined to the gearbox mainshaft, passes the drive to an intermediate gear cluster supported on a single shaft and rotating on taper roller bearings.
• The intermediate gears pass the drive to high and low speed gears on the rear output shaft. The rear output shaft passes through the speed transducer drive housing, which also forms the mounting for the park brake. A worm gear installed to the rear output shaft drives a pinion installed in the speed transducer housing.
• Integral with the output shafts is a differential assembly which compensates for speed differences between the front and rear prop shafts. To prevent all the power being transmitted to the axle offering the least resistance, a diff-lock is provided. Selection of differential lock engages, through mechanical linkage, a dog clutch with the front output shaft, this action locks the center differential and provides a fixed drive, giving equal power to the front and rear output shafts.
• The diff-lock should only be engaged during severe off-road conditions and should be disengaged as soon as conditions permit.
• A shiftlock device, used as a park facility, is installed and prevents accidental gear disengagement when the ignition is switched off. An audible neutral alarm is also installed to alert the driver, when parking, to move the gear lever to the high or low position.

INTRODUCTION
The LT230Q transfer box is mounted at the rear of the main gearbox and transmits drive to the front and rear axles via the propeller shafts. The LT230Q, while similar to the LT230T differs mainly in the following areas:
• Helix angle of gears increased to 31° together with an increase in the number of gear teeth thus giving quieter running and an increase in power transmission efficiency.
• Increased length mainshaft input gears together with increased thickness bearing housing and repositioned bearing.
• Redesigned intermediate gear bearings. Redesigned high gear bush giving quieter running

CONSTRUCTION
The transfer box comprises three main assemblies, the main casing, front output housing and rear output housing.
The main casing carries the mainshaft input gear, the intermediate gears and the differential together with the high/low range gears, selector shaft and fork.
The front output housing carries the front output shaft and flange, high/low cross shaft, housing and selector and the differential lock selector shaft and fork. A dog clutch on the front output shaft is operated by the differential lock selector fork to engage/disengage the differential lock.
The rear output housing carries the output shaft and flange and the speedometer drive and driven gears. A mechanically operated transmission brake is attached to the housing, the brake drum being attached to the output flange.
All housings and cover plates are sealed to the main casing by sealant; mud and water ingress being prevented by mud shields and throwers located at each end of the output housings and on the output flanges.

MAINSHAFT INPUT GEAR
• The gearbox output shaft is splined into the mainshaft input gear which is supported by taper roller bearings.
• Input gear bearing pre-load is achieved by the use of a selective shim located in the bearing housing. An additional power take-off gear is located at the rear of the input gear for certain applications.
INTERMEDIATE GEARS
• The intermediate gear cluster is supported by taper roller bearings located at each end of the cluster and running on the intermediate shaft which, in turn, is supported at the front and rear by the main casing.
• Intermediate gear bearing pre-load is achieved by means of a collapsible spacer positioned between the bearings, the amount of compression applied to the spacer is by means of a nut on the end of the intermediate shaft.

DIFFERENTIAL ASSEMBLY
• The differential assembly is supported at the front and rear by taper roller bearings, the bearing outer tracks being located in the front and rear output housings. Bearing pre-load is achieved by means of a selective shim located in the front output housing.
• The differential rear shaft carries the low range gear, high/low selector sleeve and hub, high range gear and bush and the differential rear bearing; these components being secured to the shaft by a special nut.
• The differential assembly comprises front and rear half carriers with integral shafts and sun and planet gears mounted on cross shafts within the half carriers. Dished, non-selective thrust washers control the engagement of the planet gears with the sun gears while selective thrust washers are used to control the engagement of the sun gears and load to turn of the differential. The differential carrier halves are bolted together, a retaining ring providing positive location of the cross shafts.
• The high/low selector shaft and fork are located at the side of the differential, movement of the shaft, fork and selector sleeve being controlled by the high/low selector finger. A spring loaded detent ball installed in the main casing locates in grooves in the shaft.
• For certain markets, a neutral warning lamp switch operated by the high/low selector shaft and an interlock solenoid are installed in the main casing.
FRONT OUTPUT HOUSING ASSEMBLY
• The front output shaft is supported in the front output housing by a single bearing and is splined into the differential front shaft.
• The high/low cross shaft is located in a housing bolted to the top of the output housing and is connected to the high/low selector finger which locates in a slot in the selector shaft.
• The differential lock selector housing is also bolted to the top of the output housing, the selector finger passes through the housing, locating in a slot in the differential lock selector shaft. The differential lock selector shaft passes through the selector fork which is located beneath a plate bolted to the side of the output housing. A spring loaded detent ball installed in the output housing locates in grooves in the shaft.
• A differential lock warning lamp switch operated by movement of the selector fork and shaft is screwed into the top of the output housing.
REAR OUTPUT HOUSING ASSEMBLY
The rear output shaft is supported in the rear output housing by a single bearing and is splined into the differential rear shaft. The output shaft also carries the speedometer drive gear which meshes with the driven gear located in the rear output housing.

LUBRICATION
Lubrication is by splash, oil filler/level and drain plugs being located in the main casing. An oil temperature switch is installed for certain applications:

OPERATION
• The gearbox output shaft transmits power to the mainshaft input gear which is in constant mesh with one of the intermediate gears. The intermediate gears are in constant mesh with the high and low range output gears running on the differential rear shaft.
• Power is transmitted to the output shafts by locking either the high or low range gears to the differential rear shaft. This is achieved by means of the high/low selector fork, sleeve and splined hub.
• The differential lock, when applied, prevents all available power being transmitted to the road wheels offering least resistance and is especially useful for "off-road" conditions. When selected, the selector fork engages the dog clutch on the differential shaft with a gear on the front output shaft; this locks the differential and provides fixed drive thereby transmitting equal power to both output shafts.

Series 2 Discovery:


The LT 230SE transfer box is mounted at the rear of the gearbox and transmits drive via high or low reduction ratios to the front and rear axles via the propeller shafts. The high/low ratios are 1.211:1 and 3.32:1 respectively.
Transfer boxes fitted to this model have the prefixes 41D and 42D to the unit serial number. Prefix 41 D denotes that the unit is not fitted with interlock whilst 42D denotes that interlock is fitted.
Whilst similar to LT230Q transfer boxes fitted to other models, the LT230SE transfer box has certain engineering modifications incorporated which are as follows:
• Uprated torque capacity
• Modified front and rear output and cross shaft housings
• Intermediate gear bearing preload now controlled by a selective, non-collapsible spacer
• Speedometer drive and driven gears not fitted for this application
• Modified high/low hub
• Modified front output flange and mud shield
• Differential lock fitted but no longer driver operated
• Modified, cable operated, high/low selector lever and brackets
• Fixed setting of differential lock warning lamp switch
Construction
The transfer box comprises three main assemblies; the main casing, the front output housing and the rear output housing. Both output housings and all cover plates are sealed to the main casing by sealant; mud and water ingress being prevented by mud shields located on the output flanges.

Main casing
The main casing carries the mainshaft input gear, the intermediate gears and the differential, together with the high/low range gears, selector shaft and fork. The front and rear output housings are bolted to either side of the main casing.

Transmission neutral sensor
A transmission neutral sensor is fitted for North America and Japan. The sensor is connected to the BCU and is normally in the open position. The sensor provides an earth path for the BCU which then interprets the signal and activates an audible warning generated by the IDM if neutral is selected on the transfer box when the ignition is on.

Transfer box interlock solenoid
An interlock solenoid is fitted for North America and Japan. The solenoid is connected to the transfer box relay which, in turn, is controlled by the IDM. The purpose of the solenoid is to prevent neutral being selected on the transfer box when the ignition key is removed, thereby locking the box in either high or low ratio.

Camshaft input gear
The gearbox output shaft is splined into the mainshaft input gear which is supported by taper roller bearings.
Input gear bearing preload is achieved by the use of a selective shim located in the bearing housing.

Intermediate gears
The intermediate gear cluster is supported by the taper roller bearings located at each end of the cluster and runs on the intermediate shaft which, in turn, is supported at the front and rear by the main casing.
A selective spacer, positioned between the gears, preload the intermediate gear bearings when the intermediate shaft nut is tightened sufficiently to achieve the correct 'torque to turn' of the intermediate gears.

Differential assembly
The differential assembly is supported at the front and rear by taper roller bearings, the front bearing outer track is located in the front output housing and the rear bearing outer track is located in the main casing by the rear output housing. Bearing preload is achieved by means of a selective shim located in the front output housing.
The differential rear shaft carries the low range gear, high/low selector sleeve and hub, high range gear and bush and the differential rear bearing; these components being secured to the shaft by a special staked nut.
The differential assembly comprises front and rear half carriers with integral shafts and with sun and planet gears mounted on cross shafts within the half carriers. Dished, non-selective thrust washers control the engagement of the planet gears with the sun gears, whilst selective thrust washers are used to control engagement of the sun gears and 'torque to turn' of the differential. The differential carrier halves are bolted together, a retaining ring providing positive location of the cross shafts.
The high/low selector shaft and fork are located at the side of the differential, movement of the shaft, fork and selector sleeve being controlled by the high/low selector finger. A spring loaded detent ball fitted in the main casing, locates in grooves in the shaft.

Front output housing
The front output housing carries the front output shaft and flange, high/low cross shaft, housing and selector and the differential lock selector shaft and fork.
The front output shaft is supported in the housing by a single bearing and is splined into the differential front sun gear.

High/low selector
The high/low cross shaft is located in a housing bolted to the top of the output housing and is connected to the high/ low selector finger which locates in a slot in the selector shaft.

High/low detect switch
A high/low detect switch is fitted in the front output housing and connects to earth when low is selected. The switch is connected to the engine ECM, the SLABS ECU and the BCU. The purpose of the switch is to enable selection of the hill descent feature and to modify the engine fueling and automatic gearbox gearshift maps stored within the respective ECM's and ECU's.

Differential lock
The differential lock selector housing is bolted to the top of the output housing, the selector finger passes through the housing, locating in a slot in the differential lock selector shaft. The differential lock selector shaft passes through the selector fork, which is located beneath a plate bolted to the side of the output housing. The selector fork engages the dog clutch sleeve with the differential rear shaft when the splines of the sleeve and differential rear shaft are aligned. A spring loaded detent ball fitted in the output housing locates in grooves in the shaft.
The function of the differential lock used in previous applications is performed on this vehicle by the Electronic Traction Control System. However, for the purposes of 2 wheel rolling road testing, the differential lock components are retained. For all driving conditions however, the differential lock must be set in the unlocked position.
The differential lock must only be engaged for 2 wheel rolling road testing as engagement of the lock disables the traction control feature and inhibits correct operation of the electronic brake distribution and hill descent features. It will also be necessary to disconnect the propeller shaft from the transfer box output shaft driving the axle whose wheels are NOT on the rolling road. The lock may be engaged/disengaged by using a 10 mm open ended spanner on the flats machined on the differential lock selector shaft.

Differential lock warning lamp switch
A differential lock warning lamp switch connected to the SLABS ECU and operated by movement of the selector fork and shaft is screwed into the top of the output housing. The switch connects to earth when the differential lock is engaged.

Differential lock warning lamp
The differential lock warning lamp is located in the instrument pack and provides a warning to the driver when the ignition is switched on that the differential lock is engaged. With the lock engaged, the traction control and electronic brake distribution warning lamps will also be illuminated. Disengagement of the differential lock should be carried out with the ignition switched off. The warning lamps must be extinguished when the ignition is switched on again.

Rear output housing
The rear output housing carries the output shaft and flange. A cable operated transmission brake is attached to the housing, the brake drum being attached to the output flange.
The rear output shaft is supported in the housing by a single bearing and is splined into the differential rear sun gear.

Lubrication
Lubrication is by splash, oil filler/level and drain plugs being located in the main casing.
Internal pressures caused by thermal expansion and contraction are avoided by the use of a plastic breather pipe venting the interior of the box to atmosphere. The pipe is attached to the top of the high/low selector housing by a banjo bolt and is then routed in a continuously rising path into the engine compartment where the open end is secured by a clip attached to the engine cylinder block.

Oil temperature warning lamp switch
An oil temperature switch is fitted to V8 engine models. In the event of the transfer box oil approaching maximum recommended working temperature of 145°C (293°F) , the switch will close and a warning lamp in the instrument pack will be illuminated.

Operation
The gearbox output shaft transmits power to the mainshaft input gear which is in constant mesh with one of the intermediate gears. The intermediate gears are in constant mesh with the high and low range output gears running on the differential rear shaft.
Power is transmitted to the output shafts via the differential assembly by locking either the high or low range gears to the differential rear shaft. This is achieved by means of the high/low selector fork, sleeve and splined hub.