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CHAPTER 2

TORQUEFLITE COMPONENTS AND OPERATION

It is easier troubleshooting, repairing, or modifying any assembly when you know how it works; TorqueFlites are no different. Unlike some of the other common 3-speed transmissions, a TorqueFlite shifts from a one-way roller clutch to a band, releases the band, and adds another clutch. This band-to-clutch shifting requires critical timing. This method makes TorqueFlites lighter, easier to work on, and often cheaper to repair.

TorqueFlites were used in some unique muscle cars. This 34,000-mile 1970 AAR Cuda 340 6-barrel has an automatic and TA Challenger engine decals.

To become familiar with the TorqueFlite’s parts, Chrysler’s part names are used throughout, and the part’s purpose, location, and relationship to others is explained in this chapter to make the disassembly and reassembly logical and understandable. And, even though most know the positions identified on the push-button display, steering column, or console as “1, 2, 3” or “First, Second, Third,” or maybe “Low, Second, Drive,” the Chrysler names of “Drive Breakaway, Drive Second, and Drive Direct” are commonly used.

Please note that when the A-904 is discussed, the A-998 and A-999 (and the later numerical-alphabetical codes) are usually being referenced. The A-727 and its later alphanumeric coded versions are usually discussed together as well.

The Components

The A-904 and A-727 have about the same amount and style of components. The only real difference is their size and credit goes to the designers for reducing the size rather than altering their great design.

Torque Converter

A manual transmission–equipped vehicle depends on a clutch and flywheel to transfer engine power to the transmission. However, in an automatic transmission–equipped car or truck, there is no “true” flywheel and clutch assembly, so there must be another way to transfer motion; that way is through the torque converter.

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.

The pump’s reaction shaft fits into the torque converter to hold the stator’s hub stationary. The reaction shaft supports the input shaft internally and the front clutch retainer externally. The front clutch retainer “seals” to the support by two rings that rotate to direct oil from the pump to “apply” the front clutch piston.

The oil pump body contains an internal bushing to support the torque converter’s hub and a seal to prevent fluid leakage around it. The reaction shaft support has an internal bushing to support the input shaft/rear clutch retainer assembly. On the A-727, various-thickness fiber thrust washers prevent the front clutch retainer from wearing the reaction shaft’s journal and they set endplay. The A-904 has a small-thickness thrust washer between the pump and retainer because its endplay is adjusted by various-thickness thrust washers between the input and output shaft.

A-727 Pump and Input Shaft Differences

There have been a few A-727 pump and input shaft changes. The 1962 to 1966 versions had 1.125-inch-diameter input shafts with 19 turbine splines, whereas the 1967 through 1970 versions had 1.175-inch-diameter shafts with 24 turbine splines. Both had reaction shaft supports for narrow front clutch retainer bushings. In 1971 through 1977, the input shafts stayed 1.175-inch diameter, but the front clutch retainer bushings widened. From 1978 to 1997, the shaft and retainer bushings stayed the same, but an additional sealing ring/groove was added to the input shaft. To prevent interchange, 1978-later lock-up A-727s had only 23 turbine splines on the input shaft. ■

The oil pump has a pump body, two rotors, and a reaction shaft support with bushings, sealing rings, and seal. There are differences between non-lock-up and lock-up converter-equipped oil pumps and they can’t be interchanged.

The A-727, A-904 and Lock-Up/Non-Lock-Up Pumps

The A-904 oil pump is smaller, but the main difference between it and the A-727 is that each of its pump body and reaction shaft supports makes up one half of the assembly. When dealing with lock-up versus non-lock up pumps, the lock-up reaction shaft has three passages sealed with steel balls and the non-lock-up support has only two passages sealed with the balls. ■

The A-727 oil pump (top) uses a larger body and smaller reaction shaft support, whereas the A-904 pump (bottom) splits into two relatively equal halves.

Front Clutch Assembly

The front clutch assembly has several purposes; it holds the clutch pack to provide Drive Direct and Reverse, and the kickdown band clamps its outer surface to create Second. The clutch pack’s friction discs are lined with organic-based or paper-based material and they may have radial or waffle patterns cut or pressed into them or they may be smooth with a slight wavy shape. The retainer’s outer tabs interlock with the sun gear shell to transfer torque to the planetary assemblies.

This A-727 front clutch assembly has a bushing, a clutch retainer, two synthetic rubber lip seals, an aluminum piston, release springs, a spring retainer, a snap ring, a clutch “pack” consisting of alternating driving (friction) discs, driven (steel) plates, a thick pressure plate, and one of four different-size snap rings.

The most common A-727 front clutch retainer holds three or four friction discs and those in Hemi and 440 6-barrel cars held five.

To operate the front clutch, pressurized fluid is directed between the two sealing rings on the reaction shaft support. Oil is fed through the hole in the reaction shaft support, through the rings, and into the holes or slots in the ID of the retainer. This pressurized fluid in the retainer forces two lip seals against their sealing surface to create a closed hydraulic system. When this fluid pressure overcomes the spring force of the clutch release springs, the apply piston moves away from the rear of the retainer to “clamp” the friction (driving) discs and clutch (driven) plates together. The inner lugs of the driving discs hold the front clutch hub of the rear clutch retainer assembly. The locked discs and plates enable torque to transmit through the rotating input shaft to the clamped clutch pack assembly and, therefore, through the front clutch retainer assembly. When the fluid pressure is removed, the retainer’s release springs force the apply piston back and release the friction discs from the driven plates.

Certain heavy-duty A-727s use a four or five friction-disc front clutch retainer; others, such as this one, hold three friction discs.

Front Clutch Retainer A-727 and A-904

The A-904 front clutch assembly is smaller and has only one large release spring; the theory of operation is the same as the multiple-spring A-727. A-904s, like A-727s, use various types and quantities of friction plates and different sizes of snap rings to set clutch pack clearances. And, like the A-727, depending upon vehicle and engine usage, the A-904 has two widths of retainers to hold friction plates and driving discs. Shift qualities change by using different types and quantities of discs and plates; by varying the strength of release spring(s); by changing the clutch pack clearance, and by controlling the timing of the kickdown band release. ■

A-727s (top) use application-dependent quantities of piston return springs. A-904s (bottom) use one large spring.

Rear Clutch Assembly

One of the “busiest” assemblies in all TorqueFlites is the rear clutch; it is applied in all forward gears. The rear clutch pack is similar to the front and, in fact, the steel-driven plates are identical. However, the rear friction (driving) discs are lined with a thinner and smooth material that has only a few grooves.

The A-727 rear clutch assembly consists of sealing rings, a clutch retainer, an input shaft-front clutch hub assembly, two synthetic rubber lip seals, a cast-aluminum apply piston, a Belleville piston spring washer, a spacer ring, and a waved spring (snap ring). It also has an apply pressure plate, alternating driving discs and driven plates, an outer pressure plate, and one of four snap rings.

This retainer is light and easy to assemble but higher tooling costs may have prevented production.

This is a never-released stamped A-727 rear clutch retainer and input shaft.

The operation of the rear clutch assembly mirrors the front. Pressurized fluid is directed through sealing rings on the input shaft, through the channel in the input shaft, and into the retainer. This pressurized fluid forces the lip seals against their sealing surfaces and the piston pushes away from the retainer to drive the Belleville piston spring-pressure plate assembly and clamp the clutch pack. During Drive Breakaway (Low or First gear), the rear clutch assembly holds a larger torque load than the front clutch; the Belleville piston spring is a lever that multiplies the apply force from the apply piston to adequately clamp the friction discs and drive plates. The Belleville piston spring also holds the apply piston in place when the clutch is non-operational during Park, Reverse, or Neutral.

Once the driving plates and friction discs are clamped in the rear clutch assembly, power transmits from the torque converter turbine, through the input shaft, to the locked clutch-pack, and to the front annulus gear. The annulus gear “rotates” the front planet carrier, which is part of the front planetary assembly.

Servos, Accumulator and Bands

Most late A-727s have a controlled-load servo kickdown servo piston assembly. It applies the kickdown band at the correct time and cushions the 3–2 downshift. The earlier basic servo assembly uses no internal spring/piston assembly and was found in pre-1971 transmissions and some later applications where soft down shifts at higher torque loads would be detrimental. The A-904s also uses the two styles of servo piston assemblies.

A Very Important Steel Ball

A steel check ball is used in the rear clutch apply piston and front clutch retainer. When the retainers are spinning but not hydraulically operating, residual fluid can force the apply piston against the pressure plate in the front clutch or the Belleville piston spring in the rear. This fluid may force the friction plates and driving discs together creating “clutch drag.” The steel ball acts as a check valve and lets fluid (under pressure due to the clutch assembly spinning) out of the retainer before the piston inadvertently clamps clutches together. ■

A-727 and A-904 Rear Clutch

The A-904 rear clutch assembly is smaller but operates like the A-727. A difference is that the A-727 assembly is two separate pieces but the A-904 is one. ■

Similar in operation, the A-727 (top) and A-904 (bottom) rear clutch retainers differ in size.

These are A-727 servos, bands, accumulators, and associated springs and levers. The kickdown band apply lever, above the C-shaped flexible kickdown band, comes in different ratios, depending on transmission usage. The low-reverse band and its hardware are on the right.

Higher-performance transmissions used apply levers with 3.8:1, 4.2:1, or a 5.0:1 ratios. The higher ratio levers multiply the apply force more to tighten the kickdown band harder around the front clutch retainer but may take longer to do so, creating timing issues if used incorrectly.

Throughout its production, A-727s had different styles of kickdown bands. Some were cast and maintained their circular shape; others are flexible and don’t retain their shape. These are known as “Flex” bands and most late TorqueFlites had them.

The Hemi and 440 6-barrel TorqueFlites had wider kickdown bands to stop the heavier and wider five-friction disc front clutch retainer during the 1–2 shift. The bands fit the five-friction disc A-727 retainers but are too wide for the standard retainers. With equal line pressure, the wider kickdown band, with the 5.0:1 ratio apply lever, produced greater holding power than the standard-width stock cast or flex kickdown band combination.

The accumulator piston and spring combination cushions the application of the kickdown band during the 1–2 upshift and the application of the rear clutch when the gearshift is placed in any forward driving range. When placed in a forward gear, the application of the rear clutch is not completed until the accumulator seats against the valve body’s transfer plate. The 1–2 upshift is not completed until the accumulator piston has moved its maximum distance in the opposite direction. This is why the type of spring (or lack of it) in the accumulator circuit affects rear clutch engagement and 1–2 upshift quality.

The low-reverse band and servo are similar between the two families of TorqueFlites, but the A-727 has only one width of low-reverse band. It applies to clamp the low-reverse drum in Reverse and in Manual Low; the low-reverse band works with the overrunning clutch to hold the low-reverse drum stationary. The A-904 and A-727 depend on the low-reverse band’s additional holding power to prevent breakage of the overrunning clutch race during hard acceleration.

Kickdown and Low-Reverse Bands

The TorqueFlite uses different widths and styles of kickdown bands to stop the front clutch retainer’s rotation. The A-904 kickdown band is smaller than the A-727’s. Most A-904s are the same width, but some A-998 and A-999s have a five-friction disc front clutch retainer and use a wider kickdown band. The A-904 started with cast, round bands but later switched to “flex” bands.

The low-reverse bands are similar but the A-904 uses two different types of bands. One is a double wrap band, used to give greater low-reverse drum holding capability for V-8 vehicles. The other is a single wrap band, which has less torque-holding capability for use with 4- and 6-cylinder engines.

Later 1970s TorqueFlites had flexible or “flex” kickdown bands. The larger A-727 band is above; the A-904 band is below.

The A-727(left) uses a single-wrap low-reverse band; the A-904 (right) uses a double-wrap band for V-8 applications.

Planetaries, Output Shaft and Governor

Three separate assemblies, the planetary gear assemblies (planetaries), the output shaft and governor, and the output shaft support bearing transfer and time torque changes. The planetaries and sun gear provide gear reduction and rotation reversal to create three forward gears and Reverse. The output shaft transfers engine torque from transmission to driveshaft. The governor controls the shifts and a bearing supports the shaft.

The front annulus gear splines to the rear clutch retainer friction discs, and the gear surrounds and drives the front planet carrier. Depending on which gear the transmission is in, the sun gear–driving shell assembly is driven by the front or rear clutch packs and may transmit torque to the rear planetary assembly. Thrust washers prevent wear between the various rotating parts and control the overall endplay.

The output shaft has a thrust washer between it and the input shaft that is fiber or bronze, depending on the transmission. Later model A-727s and A-904s have a hardened steel washer between a bronze washer and the output shaft. The output shaft has four sets of splines; small ones fit in the front planet carrier, a second set holds the rear annulus gear, a third holds the governor-park assembly, and the longest set is for the drive shaft yoke. The shaft also has worm gear teeth to drive the speedometer gear.

On the front of A-727 planetary assemblies (from left to right), a snap ring holds the planetaries on, a front planetary gear, thrust washer, front annulus gear, thrust washer, sun gear-driving shell assembly, thrust washer, rear planetary gear, thin steel thrust washer, and rear annulus gear. The last three parts are contained “inside” the low-reverse drum. The govenor and bearing also mount on the shell.

The governor assembly and output shaft support bearing are held on the output shaft by snap rings. The governor creates a hydraulic signal, which works with the throttle pressure circuit to control shift points according to the vehicle speed and torque requirements. Two sealing rings, the governor body-park pawl assembly, and the governor valve-weight-spring assembly create and deliver the governor signal to the valve body. A thin snap ring holds the governor body-park pawl assembly to the output shaft. The output shaft bearing supports the shaft and internal components and is held on by one (A-904) or two (A-727) thick snap rings.

A Planetary Assembly and Output Shaft Comparison

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.

The converter, pump, rear clutch, overrunning clutch, and governor are all highlighted in red to indicate their use in Drive Breakaway. The rear clutch is applied and the overrunning clutch is locked.

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 spins up almost immediately to create Direct Drive.

Power Flow: Drive Direct

With the valve body and governor now creating the signal, the rear clutch plates stay applied, the kickdown band releases the front clutch retainer allowing it to spin, and its clutch plates clamp together, locking the front clutch retainer to the rear clutch hub and the sun gear driving shell. The front clutch retainer is now spinning at engine speed and in the same direction, so the sun gear shell does the same. The rear clutch plates are still driving the annulus gear of the front planetary assembly, which is splined to the output shaft, and it also is at engine speed and rotating in the same direction. Because there are now two parts of the same planetary gear set running at the same speed in the same direction, the planetary assembly is essentially one solid unit. When this occurs, the planetary transfers the same power out of it as that put into it, in other words, it spins at engine speed. Because it is splined to the output shaft via the rear annulus gear, the output shaft is driven at engine speed. Drive Direct gets its name because engine speed is transferred “directly in a 1:1 ratio” through the transmission.

In Drive Direct, the rear clutch holds the front planetary annulus gear and the front clutch holds the sun gear shell/sun gear. Because two parts of the same planetary assembly are rotating at the same speed (engine speed), the planetary that is splined to the output shaft is rotating at that speed to provide Direct Drive or a 1:1 input/output shaft ratio.

Block Diagram: Reverse Gear

When the TorqueFlite shift selector is placed into Reverse, the rear clutch assembly, used in all Forward gears, gets no fluid so the friction discs and driven plates are not clamped/applied. However, the front clutch now has fluid pressure directed to it, clamping the friction plates to the steel discs locking the front clutch assembly to the front clutch hub-input shaft assembly. Along with application of the front clutch, fluid is also directed to the low-reverse servo, clamping the low-reverse band around the low-reverse drum/rear planet carrier assembly.

Hydraulically, there are exciting things happening in Reverse. Governor pressure is ignored and line pressure can be from about 160 to 270 psi (normal line pressure is 55 to 90 psi). It may not be obvious why Reverse requires such high line pressure until the mechanism of the front and rear clutch assembly is compared. The rear clutch pack is clamped in all Forward gears and it uses a Belleville spring washer to multiply piston apply force to transmit engine torque through the clutch pack. Unfortunately, the front clutch has no “force multiplying device” other than a slightly larger surface area of the apply piston. Because Direct Drive is the only other time the front clutch assembly is applied and the vehicle is already in motion, no extraordinary holding power is needed to lock the front clutch friction discs to the steel-driven plates. However, with the selector in Reverse, the vehicle is likely stationary and greater torque has to be transmitted through the applied front clutch plates. Therefore, through a couple of hydraulic changes, line pressure is almost tripled to provide the clamping force the front clutch assembly needs to transfer the power.

The assemblies in red that work to provide Reverse are the converter, pump, front clutch, and rear servo/low reverse band. No governor signal is needed. Reverse gives the rear clutch a break, but the low-reverse band and front clutch are now applied.

For Reverse, the front clutch holds the sun gear to transfer power into the rear planet carrier. However, the low-reverse band holds the planet carrier via the low-reverse drum. With the planetary held and the sun gear rotating, all that can happen is the annulus gear rotates at a 2.2:1 input/output shaft speed ratio. The annulus gear reverses direction, and it is splined to the output shaft so it also reverses, providing a way to back up the vehicle.

This summary chart helps you remember “What’s on When.”

Power Flow: Reverse

Unlike in forward gears, with the selector in Reverse, the rear clutch is not applied. In Reverse, the front clutch friction and driven plates clamp together, which locks the clutch retainer to the sun gear driving shell and the sun gear. This assembly rotates the same direction as the engine. In addition, the low-reverse band clamps the low-reverse drum stopping it. Therefore, the sun gear rotates with the engine, the rear planet carrier is held by the low-reverse drum/low-reverse band, and the annulus gear has to rotate, but in this case, it reverses direction. The engine torque transfers from the rear planet’s pinion gears to the rear annulus gear splined to the output shaft. The output shaft now rotates in the opposite direction as the engine, and at a ratio of ~2.20:1 (input-to-output shaft speed). Engine torque transfers through the transmission and with the output shaft rotating in the reverse direction, the vehicle backs up.

Clutch and Band Application

As a reminder of how the Torque-Flite components combine to create various gear ratios and rotations, see the simple clutch and band application chart.