Overhaul - ZF 4HP 18: Description

The ZF 4HP 18 Automatic Transaxle (A/T) has 4 speeds, providing an overdrive ratio of .74:1. A/T shifting is controlled by a governor valve, line pressure valve, throttle pressure regulator valve and a modulator valve. Valve operation is dependent on shift lever position, vehicle speed and throttle position. The A/T features a lock-up type torque converter and a planetary gear set, consisting of a total of 6 planetary pinions. Ignition TDC sensor is activated by a stamped steel trigger wheel attached to the torque converter drive plate. Two types of one-way clutches are used: roller and sprag. Roller type clutch operates in 4th gear, and a sprag type clutch in 2nd gear.