The TCC acts similar to a clutch in a manual transmission vehicle, in that at speeds above 35 MPH a combination of engine vacuum- and temperature-sensing valves, and a dedicated brake switch - and in later models an ECU - activated a solenoid which engaged a clutch physically locking the impeller and turbine inside the torque converter together causing engine power to be transferred directly to the transaxle.

The solenoid that controls this is notorious for failure due to overheated plastic componentry, and problems indicated by an engine stall when stopping from speeds greater than 55 MPH.

Virtually no internal parts were shared with the 125, and overdrive was achieved by departing radically from the standard single Simpson compound planetary gearset's common sungear layout.

A version of the 4T60 called the 4T60-HD, which incorporated upgraded final drive hardware but was otherwise mechanically indistinguishable from standard units, was used in the 1989-1990 Pontiac Grand Prix with the turbocharged engine.

However, issues with failures due to lack of fluid lubrication to critical clutch train parts in the relatively complex and compact design, led to the introduction of transverse FWD 4-speed automatics being delayed as an option until 1984 for the 1985 model year.