Like other internal parts, A-904 planetaries, its output shaft, and governor assembly are smaller than those in A-727s. Depending on engine size and application, the A-904 and A-727 use three or four (and some five) planet pinion gears in the planet carrier assembly. The four- and five-pinion setups are usually found in higher-performance units. ■
A-727s and A-904s use the same type of parts to achieve low and intermediate gear ratios. A-904s have smaller components, but later versions have a wider ratio gear set to work with steeper rear axle ratios.
The control valve body consists of a filter, separator plate, transfer plate, and upper valve body with associated valves, springs, balls, and end plates. Lock-up converters required an additional small valve body and tube. Later versions had electronic solenoids.
Control Valve Body and Filter
The control valve body is the “brain” of the transmission. It uses hydraulic signals from the governor, the throttle pressure rod or cable, and the manual shift valve, and combines them with fluid pressure from the oil pump to time and control all transmission functions. The valve body plates, fluid passages and restrictions, springs, and valves modulate the fluid pressure and control the timing and firmness of band and clutch application. Lock-up transmissions have a small, separate valve body that controls converter clutch lock-up. To provide the necessary clean fluid, most TorqueFlites have a large square Dacron filter but early ones were smaller, and up until 1966, they had an additional hole for the rear pump. As alternatives, the aftermarket offers more porous, tightly woven stainless steel or brass screens.
Control Valve Bodies Interchangeability
The A-904 valve body interchanges with similar year A-727s if one hole in the transfer plate is elongated. They may have different valves, springs, and orifice sizes but operation is similar although shift quality and timing may not be adequate for the application without some modifications. ■
Overrunning Clutch
The TorqueFlite’s overrunning clutch serves a critical function in Drive Breakaway. It is a one-way clutch assembly consisting of an inner race (hub), springs, rollers, and the outer race (cam). In the A-727, the outer race is pressed into the case; in the A-904, the race rivets in.
When accelerating in Drive Breakaway or Manual Low, the inner race tries to roll in the opposite direction because of the force on the low-reverse drum by the rear planetary. The rollers are pushed by their springs so they wedge between the inner and outer race, locking the assembly to stop the rotation of the inner race. When the transmission is not in Breakaway or Manual Low, the clutch freewheels because the rollers move away from the outer race’s (cam) pinch points, letting the inner race spin.
The overrunning clutch provides a way to achieve Drive Breakaway and then it just “freewheels.” The rollers are wedged into the smaller section of the outer race (cam) by the springs, locking it.
The vehicle absolutely depends on the overrunning clutch’s 10 or 12 rollers “wedging in” in the outer race and locking the low-reverse rear drum to gain the planetary gear advantage. A low gear ratio moves the vehicle easily from a dead stop or a slow roll. If the TorqueFlite is “slammed” into Drive from Park or Neutral, or if the transmission has been modified so it has no accumulator cushioning during Drive Breakaway application with the throttle on hard, the overrunning clutch’s outer race may be damaged. And, if not all 10 or 12 rollers touch at the same time, the force per area of those touching is increased. Anything that dramatically shocks the inner and outer race can potentially cause an overrunning clutch explosion
Speedometer Assembly
The speedometer gear has different quantities of teeth, depending on the rear axle ratio and tire size. The output shaft drives the speedometer gear, which is held in a rotatable/adaptable housing that accommodates all of the different gears. The adapter housing uses an O-ring on its outer diameter and a lip seal in its inner diameter.
The TorqueFlite in Operation
Now that the TorqueFlite components’ locations and purposes have been covered, the transmission can be discussed as a complete hydraulic-mechanical unit. A block diagram of the transmission in each gear shows its operation and a power flow diagram highlights the parts to show how clutches and bands transfer power.
Block Diagram: Neutral and Park
Neutral and Park are similar; neither have applied or functional hydraulic units. With no clutches or bands applied, the spinning input shaft (as part of the front clutch hub/retainer assembly) and its rear clutch pack do nothing. Because the friction discs and these steel driven plates are not hydraulically clamped, the friction discs (which spline to the front annulus gear) freely spin, and the annulus gear just “idles.” Therefore, power from the engine does not pass through any clutch assembly.
However, there is a mechanical difference between Neutral and Park. To lock the output shaft in Park, a piece of linkage is pushed into the parking gear lever by a cam/ball on the parking linkage (non-cable shift). Therefore, the parking gear-governor assembly (splined to the output shaft) can’t rotate and neither can the output shaft.
This speedometer gear housing and adapter rotates to adapt to contain almost any size of speedometer gear.
The converter and pump are shown in red to indicate that they are the only units “operating.” The pump is pumping and the converter is spinning, but not much else is happening because in Neutral or Park, no clutches or bands are applied.
There is also a hydraulic difference between Neutral and Park: “intentionally” reduced line pressure. When the shift lever or button is in Park, the “park” location of the manual valve (inside the valve body) allows fluid to leak by one land, causing a line pressure drop. Lower pressure in Park keeps the converter from filling completely and loading the engine unnecessarily. When the transmission is in Neutral however, the converter fills because there are no “controlled leaks” in the valve body. This is why the Torque-Flites’ fluid level is checked in Neutral. If the level is checked in Park, it appears higher because the converter is not filled. Checking in any other gear is also incorrect because fluid will be use by hydraulic units.
Delayed Engagement in Drive
Some TorqueFlite-equipped vehicles have a delay after shifting to a forward gear from Park. This is caused by the converter not being filled/charged in Park; one remedy is to start the vehicle in Park and immediately shift to Neutral filling the converter. Some shift modification kits address/correct this with a different manual valve and changes to the valve body. ■
Block Diagram: Drive Breakaway
When the shift lever or push button is put in Drive, the rear clutch pack clamps together applies). The rear clutch’s friction plates, now locked to the driven plates, rotate the front annulus gear, which rotates the pinions, and spins the sun gear in a reverse direction. The sun gear rotates the pinion gears of the rear planetary in the same direction as the engine, providing gear reduction.