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Although not strictly a part of classic torque converter design, many automotive converters include a lock-up clutch to improve cruising power transmission efficiency and reduce heat. The application of the clutch locks the turbine to the impeller, causing all power transmission to be mechanical, thus eliminating losses associated with fluid drive.
For the 1981 model year, a lock-up torque converter was introduced which coincided with the new EMC control of most GM cars; this version is the THM350-C, which was phased out in 1984 in GM passenger cars for the 700R4. Chevrolet/GMC trucks and vans used the THM350-C until 1986. The lock-up torque converter was unpopular with transmission builders.
Many TCUs now have an input from the vehicle's traction control system. If the TCS detects unfavourable road conditions, a signal is sent to the TCU. The TCU can modify shift programmes by upshifting early, eliminating the torque converter lock-up clutch application, and also eliminating the first gear totally and pulling off in 2nd. [3]
The early model C4 (1964–1969) used a .788-inch 24-spline input shaft, which was upgraded in 1970 to 26-spline and .839-inch. The upgrade also included a matching 26-spline clutch hub. In 1971, Ford went to a 26/24-spline input shaft, meaning the torque-converter side is 26-spline and the clutch hub is 24-spline.
During the 1980s, automatic transmissions with four gear ratios became increasingly common, [31] and many were equipped with lock-up torque convertors in order to improve fuel economy. Electronics began to be more commonly used to control the transmission, replacing mechanical control methods such as spring-loaded valves in the valve body.
A variable force solenoid (VFS) is an electro-hydraulic device that controls pressure proportionally or inversely proportionally to a signal (voltage or current) obtained from the on-board controller of a powertrain. A low flow VFS is used as a signal level devices for transmission line pressure control or application of clutches.
Muncie SM420 transmission — 4-speed manual used up to 1967, very similar to sm 465 except small changes to gear ratios and location of reverse. New Process Gear NP435 - 4-speed longitudinal transmission used in a select handful of 67-72 GM pickups
The 4L80-E uses two shift solenoids, initially called Shift Solenoid A and Shift Solenoid B; they were later changed to comply with OBD-II regulations to 1-2 shift solenoid and 2-3 shift solenoid. By activating and deactivating the solenoids in a predetermined pattern by the PCM, four distinct gear ratios can be achieved.