Most A-904s and many A-727s have 10.75-inch-diameter converters; on A-727s, these are described as having wide-ring gears. The A-727 11.75-inch converters are known as narrow-ring-gear units. The converter diameter changes but the ring gear diameter stays the same. This is a late-1970s high-stall, non-lock-up unit.
The torque converter multiplies torque and couples the engine to the drivetrain, hydraulically through fluid transfer or mechanically through a lock-up clutch. By multiplying engine torque, it makes an automatic vehicle more drivable, enables it to run lower numerical gears, and with a lock-up converter, the fuel economy is almost equal to manual transmission–equipped vehicles.
A non-lock-up torque converter has three active elements: an impeller, stator, and turbine. The lock-up torque converter has another key element: the clutch assembly.
The impeller is integral to the rear half of the converter, and because of its vane curvature and its rotation with the engine, it throws fluid into the turbine, creating a fluid coupling. A finned stator is added between the impeller and turbine to give direction to fluid thrown between the two. By redirecting the fluid, the stator’s fins make the turbine’s fluid hit the impeller’s fins harder adding torque to the input shaft.
A-727 lock-ups have a friction lining bonded to the front cover. A piston between the turbine and cover forces a pressure plate into the friction material, locking the turbine to the cover to directly couple the engine and transmission.
The torque converter has an impeller integral in the housing, front cover, turbine, stator, ring gear, and, if a lock-up unit, a clutch and apply piston. This is a truck A-727 low-stall, lock-up version.
The torque converter has a hub to drive the transmission’s oil pump via slots or flats that engage the inner rotor of the pump.
In summary, the torque converter:
1. Couples (hydraulically/mechanically) the engine and transmission.
2. Drives the oil pump.
3. Multiplies engine torque.
4. Often provides a ring gear for starting.
Disassembled TorqueFlite
The disassembled A-727 Torque-Flite (PK4039537) used for photographs came out of a 1977 318- to 360-ci truck. It was functional, had not been modified, but it had a few issues.
Here is an “exploded” A-727.
All of the internal parts are displayed roughly in the order they come apart.
TorqueFlite Case Assembly
The parts have to be contained inside a housing, which is the case. This one is for the small-block Chrysler engine. Like most two-wheel-drive trucks and cars, it has a long extension housing (but not the heavy-duty truck version).
This A-727 case assembly has cooler line fittings, a kickdown band adjusting screw, a shifter shaft seal, and a neutral starting switch. Between the case and housing is an output shaft support and extension-housing gasket. To the right is the extension housing with parking-gear lever and a bushing. It has an extension housing seal with or without a boot to protect the sliding yoke. Below is the oil pan, gasket, and attaching bolts.
Along with other external features, this case contains the neutral starting switch that performs a couple of functions: it allows the engine to start only in Park or Neutral and it passes electrical current to the reverse lights when it is in Reverse. This style of switch was used after 1968; earlier models had reverse lights controlled from another switch by the steering column, in the push-button module, or the console shifter.
To support the output shaft, there is an output shaft support that bolts to the case. The support also provides a bearing surface for the low-reverse drum, enables the governor-output shaft assembly to rotate inside it, supports the governor, and directs fluid to and from its weights and valves to control shift points.
Inside this extension housing is a lever that locks the output shaft in place in Park. A bushing at the housing’s end supports the driveshaft yoke, and its extension housing seal contacts the yoke to contain the fluid.
An oil pan, (the main sump for the hydraulic system) helps cool the fluid and bolts on the case. A tube with a dipstick (not shown) that enables the transmission to be filled and the fluid level checked pushes or bolts on.
Short Extension Housings for Trucks and Four-Wheel-Drive Vehicles
Some early compact trucks and four-wheel-drive vehicles have a short output shaft and extension housing. The transmission case and internals are the same, but the output shaft is short to enable a transfer case or shorter extension housing to fit. The speedometer gear is then usually found in the transfer case. The four-wheel-drive extension housing is roughly 1/3 as long as the standard housing.
The A-904 case is similar to the A-727 except that it is smaller. An easy way to identify them is to look at the oil pan or pan rail. An A-727 has an extra section on the passenger side for the kickdown servo but the A-904 has a “straight” rail.
Chrysler built A-727 cases to fit small-blocks, big-blocks, diesels, Slant-6s, and some International Harvesters, AMCs, Jeeps, and other foreign engines.
The A-904 fit Chrysler small-block and Slant-6s, some AMCs, U.S. Postal Service trucks, other makes, and Chrysler 2.2/2.5 4-cylinders in 1980s small trucks.
Four-wheel-drive trucks (and some AMC cars with A-904s) have a short output shaft and extension housing with a flange for the transfer case.
A-727 cases (left) have a “kicked-out” section and corresponding pan to accommodate the (larger) kickdown servo. The A-904 (right) has a relatively square pan and rail.
The Jeep case (left) has a different attaching bolt pattern than a typical Chrysler A-727 (right) and a A-904.
A radically different 1969 HD Slant-6 A-727 (left) case contrasts with an early 1962 cable-shifted big-block case (right).
Oil Pump Assembly
The oil pumps are all similar and provide hydraulic pressure to operate and lubricate the TorqueFlite. The A-727 internal rotor has 14 external teeth and the external rotor has 15 internal teeth. The torque converter’s hub locks into the pump’s inner rotor that meshes with the outer rotor in just a few locations. A gap is formed and when the rotors are spun, fluid is pulled into the gap and is squeezed out into a cavity close to the meshing teeth. This pressurized fluid travels through the pump body passageways, leading into the case and valve body, where it is regulated and directed to subsequent hydraulic components.
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