In Drive Breakaway, power is transferred through both planetary assemblies, providing the gear reduction to move the vehicle from a standstill or slow roll.
While in Drive/Breakaway, line pressure is directed to various valves in the valve body and to the governor. Once the vehicle is moving and the governor is spinning, the pressure signal is modulated and returned to the valve body to prepare for the 1–2 shift.
Power Flow: Drive Breakaway
The rear clutch friction and driven plates are clamped holding the annulus gear, driving the front planet carrier and rotating the inner sun gear to transfer power to the rear planetary, the rear annulus gear, and the output shaft. The overrunning clutch holds but the low-reverse band is not clamped on the low-reverse drum. With both planetaries now working, a Low gear of 2.45:1 or 2.67:1 is provided.
Block Diagram: Manual Low
When the selector lever or push button is placed in Low or “1,” another assembly gets active. Placing the selector in Manual Low usually slows the vehicle if in Drive Second or Drive Direct. A driver may also want to hold the transmission in Low longer than the governor and throttle pressure circuit normally allow. Engine braking (the slowing of the vehicle) is accomplished when the low-reverse band stops the low-reverse drum (once out of Low, the drum normally freewheels). Remember, Low is a combination of the front and rear planetary sets, and the low-reverse drum has to be stationary to hold the rear planet carrier (to provide gear reduction). When the vehicle moves from a stop while the transmission is in Low, the overrunning clutch holds the drum, but once out of Low, the drum can only be stopped by the low-reverse band.
Along with the same parts in use for Drive Breakaway, this diagram also has the rear servo/low-reverse band in red to show it is functioning in Manual Low. The rear clutch and the low-reverse band are applied with the overrunning clutch.
Power Flow: Manual Low
As in Drive Breakaway, during Manual Low, the rear clutch friction and driven plates are clamped and they drive the front planet carrier to rotate the inner sun gear, transferring power back to the rear planetary, the rear annulus gear, and into the output shaft providing a (Low) gear ratio of 2.45:1 or 2.67:1. The overrunning clutch is locked and the low-reverse band is also clamped on the low-reverse drum, providing engine braking not available in Drive Breakaway.
Manual Low versus Drive Breakaway
Note that Manual Low is basically Drive Breakaway with the addition of the low-reverse servo-band clamping the low-reverse drum; the governor signal to the 1–2 shift valve is blocked to prevent it from moving and allowing an upshift. ■
Manual Low uses the rear clutch and low-reverse band to hold the correct planetary components to provide a low gear of approximately 2.67:1 (wide ratio) or 2.54:1 input/output shaft speed. Manual Low also supplies engine breaking.
Block Diagram: Drive Second or Manual Second
With the selector or push button in Drive, the TorqueFlite shifts automatically into Second after the governor’s modulated fluid moves the 1–2 shift valve allowing line pressure to be directed to the front servo-kickdown band assembly and accumulator. (The governor signal is generated by the output shaft’s rotation, which throws the governor weights outward, working against spring pressure.) The governor pressure signal is also directed to the 2–3 valve in preparation for that shift. Along with the rear clutch (in operation) the fluid pushes the kickdown servo, actuating the apply lever to clamp the kickdown band on the front clutch retainer and stop it.
If the shift lever or push button is placed in (Manual) Second, it is the same as Drive Second with a hydraulic difference. With the lever in Second, the vehicle starts in Low and shifts to Second but the manual valve works with the line pressure to block the 2–3 shift valve preventing a 2–3 upshift. Governor pressure can’t overcome line pressure on the 2–3 valve until the shifter is placed into Drive. When manually downshifting from Drive Direct to Second, the same Manual Second circuits function preventing an upshift back to Direct while the 2–3 shift valve is blocked by line pressure.
Power Flow: Drive Second
In Drive Second, the rear clutch plates are (still) clamped and transferring power into the front planetary’s annulus gear and the front servo is now clamping the kickdown band. The band stops the front clutch retainer, which is locked into the sun gear driving shell that contains the sun gear. Because the kickdown band is holding the sun gear stationary via the sun gear shell, the applied rear clutch plates drive the front planetary annulus gear, forces the front planet carrier to rotate in engine direction at a reduced speed. Moreover, because the front planet carrier’s annulus gear is splined directly to the output shaft, the shaft now rotates at the reduced speed of roughly 1.45:1 or 1.52:1 (input speed to output speed). The overrunning clutch stays locked until the 1–2 shift completes.
The converter, pump, front servo/kickdown band, rear clutch, and governor are highlighted in red to show that they function in Drive Second. The overrunning clutch is black, even though it was required in Drive Breakaway during acceleration. Once out of Low gear/Drive Breakaway, though, the overrunning clutch freewheels. Drive Second and Manual Second depend upon the application of the rear clutch and the kickdown band.
In Drive Second, the rear clutch clamps onto and rotates one part of the front planetary; the kickdown band/sun gear shell hold the other, causing the front planet carrier to rotate the output shaft at approximately 1.54:1 (wide ratio) or 1.45:1 input/output shaft speed ratio.
Shown in red are the assemblies that hydraulically function in Drive Direct: converter, pump, front clutch, rear clutch, and governor. To create Drive Direct requires the rear clutch and the Front/Direct clutch is added as the kickdown band drops off.
Block Diagram: Drive Direct
With the selector or push button in Drive, and while the transmission is in Second, governor pressure is present on the 2–3 shift valve, the front clutch retainer has been stopped by the kickdown band, and the rear clutch is applied and rotating the front planetary and the output shaft.
Front Planetary Assembly
The power flow transfer in Second gear occurs exclusively in the front planet carrier. Tight converters combined with high-torque engines feeding power to TorqueFlites equipped with aggressive shift kits in heavy vehicles can rip the splines out of the aluminum carriers. Some combinations may require steel or modified aluminum planet carriers. ■
When the signal is allowed to push the 2–3 shift valve in the valve body, fluid is directed to the release side of the front servo, releasing the kickdown band. Fluid is also directed into the front clutch retainer and pushes the piston clamping the friction discs and driven plates together. Because the kickdown band releases quickly, the front clutch retainer