Intermediate Reduction Drive

Description
Intermediate Reduction Drive (IRD)
The IRD is fitted in place of the conventional transfer box and is attached to the manual or automatic gearbox. The combination of the two units 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 and, 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 aluminum.
The unit comprises of a main casing, a RH housing, primary shaft, an intermediate shaft, a differential unit, a laygear, hypoid gear set, a rear output pinion and a pinion housing.

An oil cooler, connected to the vehicle cooling 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.

Four seals, internal to the IRD, are used to prevent mixing of the IRD and gearbox lubricating fluids.

Operation
Drive is transmitted from the gearbox to the IRD primary shaft via the splined hub in the gearbox final drive gear carrier. The drive is then transmitted from the primary shaft gear, which is integral with the primary shaft, to the layshaft which in turn drives the differential for the front driveshafts, and via a bevel drive gear and pinion to drive the rear axle. The intermediate shaft passes through the center of the IRD primary shaft, and is the drive link between the IRD differential, and the left-hand front driveshaft, passing through the center of the final drive carrier.

Oil Seals





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.