Like the twin-disk transmission we have just discussed, the hydraulic transmission uses two friction plates to transfer drive torque to the gear mechanism. However, the hydraulic transmission does not use a floating plate to engage or disengage the clutches. The clutches are engaged or disengaged when either the forward or the reverse clutch disk is locked between a hydraulically operated piston and a drive plate. Another difference between the two types of transmissions is the use of planetary gears in the hydraulic transmission, rather than a second shaft and an idler gear, to reverse rotation of the drive shaft. This method of reversing direction will be explained later in detail. One other difference is the method by which the transmissions are lubricated. The twin-disk transmission is splash lubricated by the action of the forward gear and the reverse gear as they pick up oil from the sump and throw the oil as they rotate. The hydraulic transmission is lubricated by both pressure oil and splash oil. A central passage is open too il pump pressure a tall times when the engine is running. All moving parts inside the transmission are lubricated from this source. A nozzle at the top of the housing provides a spray of oil for lubricating the drive (pinion) gear, the driven gear, and the bearings.

The hydraulic transmission consists of a forward drive clutch assembly, a reverse clutch and reduction gear assembly, an oil pump that supplies oil under pressure for operation of the clutches, a control (selector) valve that admits oil to the clutches, and an oil strainer and oil cooler. Although there are several designs of hydraulic transmissions, if you clearly under-stand the operating principles of the Torqmatic design you should be able to understand the operating principles of other types of hydraulic transmissions.

The hydraulic transmission receives input torque through the forward clutch plate which is bolted to the aft face of the engine flywheel. Torque for forward motion is transferred from the clutch plate to the forward clutch disk. Torque for reverse motion is transferred from the forward clutch disk to the planetary gears by the sun gear. Details of the operating sequences for the neutral, forward, and reverse positions of the selector lever are provided in the sections that follow.