Intermediate Reduction Drive: Notes
The Intermediate Reduction Drive (IRD) is attached to the JATCO automatic transmission in place of a conventional transfer case. See Fig 1 . In conjunction with the automatic transmission, 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 4WD system. The main casing, cover and pinion housing are manufactured from cast aluminum.
The unit consists of a main casing, a right 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 installed to prevent overheating of IRD lubricating fluid. The main casing also incorporates the oil filler/level and drain plugs and a breather outlet. There are a total of 7 taper roller bearings and one parallel roller bearing supporting the primary shaft, differential and output shaft assemblies.
Externally, 3 oil seals prevent lubricating oil escaping from the transmission and the IRD unit. The transmission gear case houses the oil seal for the left hand front axle shaft, and the right housing on the IRD unit houses the oil seal for the right hand front axle shaft, with the remaining oil seal located in the pinion housing of IRD.
There are also 4 internal oil seals in the IRD unit. There are 2 smaller diameter oil seals installed internally at each end of 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 transmission along the intermediate shaft. There are 2 larger oil seals installed in the main casing where IRD unit enters the transmission. The inner oil seal prevents oil ingress from the IRD primary shaft entering into the area between the 2 seals, and the outer oil seal prevents oil ingress from the transmission 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, installed in a machined groove, seals IRD main casing to transmission housing.
The unit is comprised of a main casing, a right housing, a primary shaft, an intermediate shaft, a differential unit, a laygear, hypoid gear set, a rear output pinion and a pinion housing.