Freelander IRD

Freelander Intermediate Reduction Drive (IRD) Unit

General
The Intermediate Reduction Drive (IRD) is attached to the JATCO automatic gearbox in place of a conventional transfer box. In conjunction with the automatic gearbox, it provides drive to the front and rear wheels. The IRD incorporates a differential unit to control the proportion of drive delivered to each front wheel. In addition, it operates in conjunction with the viscous coupling to give the vehicle a self-sensing four wheel drive system. The main casing, cover and pinion housing are manufactured from cast aluminium.

The unit consists of a main casing, a RH housing, primary shaft, an intermediate shaft, a differential unit, a lay gear, hypoid gear set, a rear output pinion and a pinion housing. An oil cooler, connected to the engine coolant system, is fitted to prevent overheating of the IRD lubricating fluid. The main casing also incorporates the oil level/drain plugs and a breather outlet. There are a total of seven taper roller bearings and one parallel roller bearing supporting the primary shaft, differential and output shaft assemblies.







Externally, three oil seals prevent lubricating oil escaping from the gearbox and the IRD unit. The gearbox gear case houses the oil seal for the left-hand front driveshaft, and the RH housing on the IRD unit houses the oil seal for the right-hand front driveshaft, with the remaining oil seal located in the pinion housing of the IRD.

There are also four internal oil seals in the IRD unit. Two smaller diameter oil seals are fitted internally at each end of the primary shaft. These prevent oil ingress along the intermediate shaft from the IRD unit at the differential end. At the opposite end, the seal prevents oil ingress from the gearbox along the intermediate shaft. Two larger oil seals are fitted in the main casing where the IRD unit enters the gearbox. The inner oil seal prevents oil ingress from the IRD primary shaft entering into the area between the two seals, and the outer oil seal prevents oil ingress from the gearbox entering the same area.

On the underside of the main casing is a 'tell-tale' drilling which is positioned between the inner and outer primary shaft oil seals. Oil leakage from the drilling will indicate either a faulty inner or outer primary shaft oil seal. An 'O' ring seal, fitted in a machined groove, seals the IRD main casing to the gearbox housing.







IRD Cooler
The IRD is cooled by an internal plate type heat exchanger incorporated into the IRD lubrication circuit.

Coolant flows from the outlet at the right front corner of the cylinder block through the hoses and the coolant rail to the IRD cooler. Coolant returns to the thermostat housing, bypasses the thermostat and flows back to the coolant pump inlet to begin the cycle again.