4WD Differentials & Axle Shafts: Description

NOTE: For axle shaft, differential, drive shaft and locking hub information on Passport, refer to Rodeo in appropriate Isuzu article.

WARNING: Under normal conditions, vehicle is in 2WD (front-wheel drive). Real-Time 4WD system will instantly transmit appropriate driving force to rear wheels (depending on driving force of front wheels and road conditions). As a result, vehicle could jump forward without warning causing severe damage and/or injury. Real-Time 4WD-Dual Pump System does not have a manual switch to disable 4WD system. Whenever service work requires rotating front or rear wheels using the engine, always raise and support vehicle so all 4 wheels are off the ground.

Differential is a hypoid-type incorporating a torque control differential case assembly containing a differential clutch assembly, companion flange, and oil pump body assembly. See Fig 1.

The oil pump body contains one front pump, one rear pump, hydraulic control mechanism, and clutch piston with a preset disc spring which provides differential clutch assembly with a preset torque to prevent abnormal sound.

The clutch guide is connected to drive shaft at the companion flange, receiving power from transfer assembly. Clutch guide rotates clutch plate and front oil pump. Rear oil pump is driven by hypoid driven gear that is splined to clutch discs contained in clutch hub. Rear pump oil capacity is 2.5 percent larger than front pump to handle rotation difference between front and rear wheels caused by worn front tires or tight corner braking. Oil pumps work as a fluid discharge when oil pumps rotate in reverse.

The real-time 4WD dual-pump system instantly transmits appropriate driving force to rear wheel automatically. The dual-pump system switches off when braking in forward gears, allowing models with ABS to operate properly. When a speed difference between front (clutch guide,) and rear wheels (hypoid driven gear) is detected, hydraulic pressure from front and rear oil pump engages differential clutch, applying drive force from transfer assembly.

Hydraulic pressure control mechanism in oil pump body selects 4WD mode when:

Vehicle starts abruptly.
Accelerating in forward or reverse, causing a rotation difference between front and rear wheels.
Braking in reverse gear (when decelerating).

2WD mode is selected when:

Driven forward or reverse with no rotation difference between front and rear wheels.
Braking in a forward gear (when decelerating).

Differential clutch assembly is lubricated by hydraulic pressure generated by oil pumps in both 2WD and 4WD modes. A thermal switch relieves hydraulic pressure to clutch piston and cancels 4WD if differential fluid temperature rises to greater than normal.

Fig 1: Identifying Differential Assembly & Hydraulic Control System Components

Courtesy of AMERICAN HONDA MOTOR CO., INC.