GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

General Information

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See Figures 1 and 2

The automatic transaxle allows engine torque and power to be transmitted to the rear wheels within a narrow range of engine operating speeds. The transaxle's design allows the engine to turn fast enough to produce plenty of power and torque at very low speeds, while keeping it at a sensible rpm at high vehicle speeds. The transaxle performs this job entirely without driver assistance. The transaxle uses a light fluid as the medium for the transmission of power. This fluid also works in the operation of various hydraulic control circuits and as a lubricant. Because the transaxles fluid performs all of these three functions, trouble within the unit can easily travel from one part to another. For this reason, and because of the complexity and unusual operating principles of the transaxle, a very sound understanding of the basic principles of operation will simplify troubleshooting.



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Fig. Fig. 1: Possible leak points on the 3T40 automatic transaxle



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Fig. Fig. 2: Possible leak points on the 4T60-E automatic transaxle

TORQUE CONVERTER



The torque converter replaces the conventional clutch. It has three functions:

  1. It allows the engine to idle with the vehicle at a standstill, even with the transaxle in gear.
  2.  
  3. It allows the transaxle to shift from range to range smoothly, without requiring that the driver close the throttle during the shift.
  4.  
  5. It multiplies engine torque to an increasing extent as vehicle speed drops and throttle opening is increased. This has the effect of making the transaxle more responsive and reduces the amount of shifting required.
  6.  

The torque converter is a metal case which is shaped like a sphere that has been flattened on opposite sides. It is bolted to the rear end of the engine's crankshaft. Generally, the entire metal case rotates at engine speed and serves as the engine's flywheel.

The case contains three sets of blades. One set is attached directly to the case. This set forms the torus or pump. Another set is directly connected to the output shaft, and forms the turbine. The third set is mounted on a hub which, in turn, is mounted on a stationary shaft through a one-way clutch. This third set is known as the stator.

A pump, which is driven by the converter hub at engine speed, keeps the torque converter full of transaxle fluid at all times. Fluid flows continuously through the unit to provide cooling.

Under low speed acceleration, the torque converter functions as follows:

The torus is turning faster than the turbine. It picks up fluid at the center of the converter and, through centrifugal force, slings it outward. Since the outer edge of the converter moves faster than the portions at the center, the fluid picks up speed.

The fluid then enters the outer edge of the turbine blades. It then travels back toward the center of the converter case along the turbine blades. In impinging upon the turbine blades, the fluid loses the energy picked up in the torus.

If the fluid were now