THE RX4 is available only with a five-speed manual transmission. All four wheels are driven permanently with a "JC7" gearbox with twin outputs, a three-section propeller shaft with two intermediate universal joints, a viscous coupling, a rear final drive and two additional driveshafts. The RX4 runs as a front-driver until both front wheels fail to find grip this generates heat and in turn solidifies silicon oil contained with the viscous coupler. With the two driveshafts turning at the same speed, power is automatically carried to the rear wheels until grip is returned to the front. Assisting the process is an electronic traction control system operating on the front wheels to ensure constant traction in most circumstances.