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Chrysler Torqueflite 727 OverviewPart 1: overview and what each part doesTorqueflites first appeared in 1956, as an option, in Imperials and 300Bs. This unit had a cast iron body with aluminum converter housing and aluminum tail shaft housing. The gear ratios were the same in the forward gears as they are now; 2.45:1 first gear, 1.45:1 second gear, and 1.00:1 direct or third gear. Reverse was 2.21:1 in the early units and 2.20:1 in all models since 1962. These transmissions were coded A-488s and were offered standard on 1957 Imperials and other Chrysler models. In fact, the 1957 Torqueflite was heralded as "the best automatic in the world."In 1962 the aluminum case was introduced. It had the code name of "727" and together with the torque converter, it weighed about 160 pounds. The original 727 was basically unchanged through 1965. Certain items were altered in the 1965 model year and these included enlarging of the torque converter splines on some 1965 models, elimination of their flanged output shaft, and changing the shift mechanism from two cables to one rod-and-lever arrangement. All of these changes have been incorporated on 904s and 727s since 1966.Modifications made since 1966 have basically been small and related to longevity and driver comfort. 1971 saw introduction of the wider front clutch bushing that eliminated premature ring and drum wear. This is the modification I consider to be the best as far as high performance application is concerned.Introduction to the TorqueFliteThe automatic transmission is a convenience item for most people. The shift lever is moved to get the car in motion and then left alone until the car is stopped. No clutch pedal to push or shifter to change between three, four, or even five forward gears makes for a minimum of driver effort. Not only were automatics originally used for general driving comfort, but they quickly found a place in competition vehicles.The 1960s were a time that Chrysler products dominated various drag strip classes, both AHRA and NHRA. The majority of the cars were running manual transmissions as they were faster and easier to repair. However, the shock of 4000 to 6000 rpm drops on the starting line created enormous loads on tires and various driveline components. If it wasn't for the fact that tires were a lot slicker then, there probably would have been an incredible amount of additional parts breakage.Chrysler was the first to develop better racing automatics since they already had the most dependable automatic transmissions on the road. It took G.M. until 1964 to develop the famous Turbo-Hydramatic 400. Up to that point in time, there was only the Powerglide being used seriously in G.M. racing vehicles.The advent of the aluminum torqueflite revealed many more classes that Chrysler could dominate. Evidently, early engineering groups at Power Train Design did their homework because the original design has changed little as Chryslers still dominate A through D stock automatic in NHRA classes.With bracket racing coming alive in the 1970s, it has been almost mandatory to have a good automatic in 90% of the classes if you want to be consistent and win races. Torqueflites still fulfill the needs of Chrysler racers.Automatics have always been four to six percent less efficient than manual transmissions. Torque converter slippage was a big contributing factor to this inefficiency; in 1978 lock-up clutch-type converters were used with Torqueflites, to help reduce the gas mileage difference between automatic and manual transmissions. I will not go into much detail on these because they are very similar in design to stock 727s and 904s with the addition of a few control valves and a slightly different torque converter.As gas mileage demands increased, thereby decreasing engine size, Chrysler changed from 727s to use of more 904-type transmissions (G.M. created the Turbo 200-type automatic for smaller vehicles, and what a money maker this has been for automatic transmission repair shops!). No real problems were noted by changing to the smaller unit except for 1978 early lock-up shuddering. This was remedied by delaying the lock-up speed a few mph later that model year.The Torque ConverterThere has to be something to transfer motion from the engine to the transmission and that item is a Torque Converter. This unit does what its name implies; it converts or "multiplies" engine torque at low speeds and couples the engine to the drive train hydraulically at higher speeds. The converter consists of three elements, all necessary for proper transmittal of motion. The Impeller and Turbine transfer fluid between each other to drive the Input Shaft of the transmission. The Stator is a device used in the converter to multiply torque by giving proper direction to the fluid flowing between the impeller and turbine. The converter hub has slots that engage the tabs on the inner rotor of the oil pump to create oil pressure and oil flow from the pump while the engine is running.The overall purpose of the torque converter is to:Provide a coupling between the engine and transmissionSupply a method of driving the transmission oil pumpProvide a unit that incorporates a flywheel for startingSupply a multiplication of engine torque of approximately 2.2:1 at low speeds and 1:1 at higher speedsRefer to either Chrysler literature or other applicable information for more details about the internal "Vortex, Rotary and Turbulent" flow of fluid if you are interested in more of the converter operation and design. Converter diameters and stall speeds will be discussed in the modification section.Torqueflite Exploded View190502931160Before going into details of each subassembly in the Torqueflite, refer to the supplies photo of the exploded view of a complete 1976-727 transmission. The over-running Clutch is not shown and the Valve Body is not a 1976 model but actually a 1970 model. There are reasons for this but they are not important to the overall explanation of the internal operations. From top left you will see the Pan, the Case, and the Tail shaft, or Extension Housing and associated hardware. The top right corner contains all the Servos, Bands, Operating levers and pins, and the Accumulator and its spring. The next row has the Oil Pump and the Front Clutch assembly shown. Row three displays the Rear Clutch assembly. The fourth row holds both Planetary Gear sets, the Front Clutch hub, Sun Gear and Sun Gear Driving Shell, and the Low-Reverse Drum assembly. To the far right is the oil filter and "Direct Connection" oil filter extension. This extension is used with the deep oil pan shown in the upper left corner. The last row contains the Output Shaft, Governor Assembly and the Output Shaft Support Bearing. To the right of this is the "Brain" of the transmission; the Valve Body.I will explain the pictures of the various units in the general order they are displayed and tell what functions the pieces have in the overall transmission operation in the following text.Torqueflite Case Assembly-952501496060Shown is a 727 case and associated pieces (the 904 is almost identical except the size and shape of everything is slightly reduced). This case is 727-A which fits all small blocks. The 727 can also be a 727-B which fits the big blocks, or 727-RG which bolts to the six-cylinder blocks. The 904 comes in a 904-A, 904-RG, as well as units for some of the earlier 4-cylinders. Some higher performance 904 units were designated as 998s and 999s in the later 1970s.The case is in the upper left corner. Below it are the cooler line fittings, the shifter shaft seal, and neutral start switch. The neutral start switch performs a couple of functions. It allows the engine to be started when the transmission is in only park or neutral range and it controls the electrical current to the reverse lights when the transmission is in reverse gear (This type of neutral switch has been used since 1969. 1968 and earlier cars had the reverse lights controlled from a switch on the steering column or console shifter).Next is the case-to-tail shaft gasket and the governor support. The governor support bolts to the case and it has a threefold purpose. It supports the low-reverse drum, the governor-output shaft assembly, and it directs oil to and from the rotating governor weights (The governor works with the throttle pressure circuit to control shift points). Next is the tail shaft housing that contains the parking gear lever (used to lock the governor-output shaft assembly in park) and the output shaft support bearing snap ring. A seal is used at the end of the housing to ride on the drive shaft yoke to keep oil contained in the case.Below all this is the oil pan (I've shown the Direct Connection deep pan with a drain plug). Its purpose is to act as a fluid source for the hydraulic system (some oil cooling is also done by the pan). Not shown is the tiller tube and the dipstick that allow the transmission fluid to be filled and have the fluid level checked from the engine compartment.Servos and Bands-2190751372235Shown in this photo are the bands necessary to give second gear (kickdown band), and reverse or manual low (low-reverse band). Here's a description of the individual parts: in the upper left corner is the low-reverse band assembly consisting of the retaining snap ring, the spring retainer, the large diameter return spring, the piston plug, the piston plug spring, the piston itself, the synthetic rubber piston seal, and the snap ring that holds the piston plug and spring to the piston.Moving to the top of the photo again, is the low-reverse lever assembly, its adjustment screw and lock nut, the pin that the lever assembly pivots on and the rectangular strut that applies the low-reverse band. Right below the band is the anchor that holds the band when the piston pushes the low-reverse lever.An accumulator spring, a cast iron sealing ring, the accumulator piston and one more sealing ring are displayed in the center of the photo. Both 904 and 727 Torqueflites use the accumulator to give a cushioned drive breakaway only, depending on which side of the piston the spring is placed.In the right half of this picture is the kickdown servo assembly, and the kickdown band. The kickdown servo assembly consists of the retaining snap ring, cast iron seal ring, the aluminum pin guide, the large servo return spring, and a controlled-load servo with its cast iron rings below it.This particular servo piston is called a controlled load servo and its purpose is to cushion the three-two downshift. The other type of servo assembly does not use an internal spring-piston assembly and it is usually found in high performance applications where soft shifts would be detrimental. Individual pieces cannot be interchanged between the standard and controlled-load servos. The apply lever at the lower right corner comes in different ratios, again depending on engine usage. Usually the higher performance transmissions use a 3.8 to 5.0 ratio lever. The higher numbered levers multiply the apply force more to tighten the band quicker and harder around the front clutch retainer drum.The 904 uses two different types of low-reverse bands. One type is called a double wrap band, very similar to the Hemi kickdown band, and it is used with the VS engines to give greater low-reverse drum holding capability. The other band is a single width band that has less torque holding capacity and is used with six-cylinder engines. The 727 also uses a single width low-reverse band and it is used with all engines.The low-reverse band works with the over-running clutch (which I've not shown) to hold the low-reverse drum during manual low. The 904 has a smaller over running clutch so it depends on the band to give it sufficient holding power to prevent breakage of the clutch. I'll explain later why the low-reverse drum must be held stationary, but for now bear in mind that the drum needs to be held during manual low, drive breakaway (or low) and reverse. The over-running clutch is like a stator in the torque converter, but its outer race is firmly affixed to the rear of the case whereas the outer race of the converter stator is free to lock-up or spin depending upon engine-vehicle speed difference.The 904 uses different kickdown bands to hold the front clutch retainer drum during second gear. Most 904s have a single width band, but some 998 and 999 versions of the 904 have a drumwith five clutches, and need a wider band to hold it. Some 904s use what is called a "flex band" that performs identical functions to the standard cast band but will not retain the circular shape of the cast band when it is removed from the transmission. 727 trans-missions also use the flex band in later model years. A double wrap band (also called the Hemi or 440-6 pack band) was used with the five clutch retainer drums that were used in the maximum performance 727s. This band was wider and could produce much greater holding power than the single width cast or flex band found on most other 727 units. One might think it wise to use the Hemi-band with the standard 727 drums but it will not work because of the width difference between the four and five clutch drums. I will explain various tricks that can be done with bands, apply levers and drums in the modification section.Oil Pump AssemblyThe oil pump provides the hydraulic pressure needed to operate the various units in the transmission. It is made up of the pump body, two rotors, and the reaction shaft support. The first rotor has 14 external teeth and the second rotor has 15 internal teeth, The rotor with external teeth is driven by the torque converter hub and it meshes with the other rotor at only a few locations thereby creating a gap. As the rotor spins, fluid is picked up in this gap and is forced out where the teeth are meshing creating pressure to drive the fluid through various passageways of the pump body (The 904 pump is physically smaller and the pump body and reaction shaft support each make up one-half of the pump body assembly).The reaction shaft holds the stator stationary in the torque converter and it supports the input shaft in its I.D. and the front clutch retainer on its O.D. The front clutch is sealed to the reaction shaft by the two cast iron rings that direct oil from the pump to the inside of the front clutch.The oil pump body has a bushing to support the converter hub and a seal to prevent fluid leakage around it. The reaction shaft has a bushing in it to support the input shaft (which is part of the rear clutch assembly), oil pump assembly.Pressure forces the lip seals against their surfaces and pushes the piston away from the clutch hub and applies force to the clutch pack through the Belleville spring-pressure plate assembly.The rear clutch has to hold a larger torque load than the front clutch so the Belleville washer is used to multiply the apply force of the piston. The Belleville washer also acts as a spring to return the piston when the clutch is not hydraulically functioning. Once the plates and discs are locked in the rear clutch assembly, power can be transmitted through the input shaft, to the locked clutch-pack and to the front annulus gear (see planetary assembly photo). Once the planetaries are utilized, you get gear reduction and torque multiplication; or in other words, first or second gear depending on planetary usage.Something not mentioned previously, but that is found in both the front and rear clutch is the check ball in the apply piston. This is not easily seen in the photos but it serves an important purpose. When the clutch is spinning but not hydraulically operating, residual fluid can be forcing the piston out against the pressure plate (front clutch) or Belleville washer (rear clutch) creating clutch drag. This ball-check valve lets that fluid (that is under pressure from the clutch assembly spinning and throwing the fluid out due to centrifugal force) out of the clutch cylinder or drum. The 904 rear clutch is smaller but operates identically to the 727. The notable difference is the front clutch hub-rear clutch retainer is two separate pieces in the 727 but they are only one in the 904.Planetaries, Output Shaft, and GovernorI've grouped basically three separate assemblies in this one photo. The planetaries and sun gear in the top row give the various gear reductions and reversals; the output shaft transfers output torque; and the governor controls the shift points. Listed here are the planetary parts: The snap ring that holds the planetaries on the output shaft, the front planetary gear, a thrust washer, the front annulus gear, another thrust washer, the sun gear-driving shell assembly, another thrust washer, the rear planetary gear, a thin thrust washer and the rear annulus gear. The last three pieces are contained in the low-reverse drum. The front annulus gear is splined to the rear clutch discs and it drives the front planetary. Depending on gear selection, the sun gear-driving shell assembly will be driven by the front or rear clutch packs and will transmit torque to the rear planetary assembly. The four thrust washers shown are needed to prevent wear between the various rotating members.The output shaft is shown with its thrust washer on the left. This thrust washer prevents wear between the input shaft and the output shaft. It is fiber or bronze, depending on the year of the transmission. The output shaft has four sets of splines cut into it. The splines on the left fit into the front planetary gear, while the second set locks the output shaft to the rear annulus gear and the third set holds the governor-park pawl assembly on the shaft. The splines on the far right are used to connect the drive shaft yoke solidly but still allow it to slide easily on the output shaft. The shaft also has gear teeth cut into it to drive the various size speedometer gears. In the lower right portion of the picture is the governor assembly and the output shaft support bearing with their associated snap rings. The bearing supports the loads imposed on the output shaft by the internal mechanisms of the transmission, and maintains the correct end play in the gear train.The governor works with the throttle pressure rod to control shift points, according to the vehicle speed and engine torque requirements. Two cast iron sealing rings, the governor body-park pawl assembly and the governor valve-governor weight assembly all work together to send the governor signal to the valve body to tell it to operate various shift valves, controlling up and down shifts. There is one snap ring used to hold the governor body park pawl assembly secure on the splines on the output shaft.As in the other units, the 904 planetarys, output shaft, and governor assembly are similar to the 727 pieces, but smaller in size. Depending on the size, both will have three or four planet pinion gears in the assembly. The four pinions will be found in higher performance units.Control Valve Body and FilterThe valve body can be considered the brain of the transmission. It takes hydraulic signals and combines these with fluid pressure to correctly time and control all transmission functions. The springs and valves work together to modulate fluid pressure to time application of the bands and clutches. The channels that resemble endless mazes transfer fluid from valve to valve, or from valve to case passageway.-190500The 904 valve body will interchange with a 727 valve body if one hole in the transfer plate is elongated. Some 727s have different valves and springs than 904s but operation is similar. The lockup units have another section added to control converter clutch lockup but everything else is similar.The valve bodies are extremely well designed, and it is hard to make a mistake while assembling them. As long as the springs are not interchanged or the balls mixed up, they always seem to work. Comparing Chrysler valve bodies with Ford units is like comparing 426 Hemis with flathead Fords, no comparison can be found. GM units are pretty slick but not as much fun to work on.The Torqueflite in OperationAfter reviewing all the previous information to get an idea what the various assemblies look like and do, the Torqueflite can now be studied as a complete unit. I'll go through a gear by gear description explaining the active components and how they combine to get the different gears. Because of the skill and generosity of a close friend, I'm able to supply a block diagram of the Torqueflite in the various gears. I've combined neutral and park on one diagram as they are very similar in operation.Park and NeutralNeutral and Park are very similar in the Torqueflite. No hydraulic units are operating and, with no clutches or bands applied, the input shaft-front clutch hub assembly and the driving discs in the rear clutch pack are rotating at engine speed. The rear clutch driving discs that are splined to the front annulus gear are free to spin, and the annulus gear is stationary. Therefore, all power flow stops at the rear clutch retainer.Mechanically there is a slight difference between neutral and park inside the transmission. Something has to lock the output shaft solid to prevent unwanted vehicle motion. This is done by a piece of linkage that connects to the parking gear lever and the valve body manual gear lever. This parking gear lever is pushed into the parking gear-governor assembly by a cam on the parking linkage. The parking gear-governor assembly is splined to the output shaft so when the gear is stopped, the output shaft is stopped.There is also a hydraulic difference between neutral and park. This is due to "intentionally" reduced line pressure. The "park" location of the manual valve (inside the valve body) allows fluid to leak by a land off the valve thereby creating a line pressure drop. This low pressure in park keeps the converter from completely filling and loading the engine unnecessarily.In neutral, the converter is filled and there are no "controlled leaks," as in park. This is the reason Torqueflites should always have the level checked only in neutral. If you check the level in park, the level checks higher than it really is.Control Valve Body and FilterAs mentioned earlier in the text, the valve body can be considered the "Brain" of the transmission. It takes the hydraulic signals from the governor, throttle pressure rod, and manual shift valve, and combines these with fluid pressure from the oil pump to correctly time and control all transmission functions.I am not going to describe each valve or spring just yet. I'll incorporate that into the modification section. For now, I'll just point out that the filter and filter extension are at the top, the valve body and associated valves, springs, balls, and end plates are on the left, the separator plate is found in the right-center and the transfer plate is at the right.The springs and valves work together to correctly modulate the fluid pressure to time application of the appropriate bands and clutches. The channels in both valve body and transfer plate that resemble endless mazes, transfer fluid from valve to valve, or valve to case passageway.The 904 valve body will interchange with a 727 valve body if one hole in the transfer plate is elongated. Some 727s have different valves and springs than 904s but operation is similar. The lock-up units have another section added to the basic valve body to control converter clutch lock-up but everything else is similar to the standard automatic transmissions.The Torqueflite valve bodies are extremely well designed. I like to work on them as it is very hard to make a mistake while assembling them. As long as the springs are not interchanged or the balls mixed up, they always seem to work. Comparing Chrysler valve bodies with Ford units is like comparing 426 Hemis with flathead Fords; no comparison can be found. GM units are pretty slick but not as much fun to work on.Sometimes Chrysler owners complain of delayed motion of the vehicle after dropping it in gear from park. This is due to the converter not being fully charged in park. The best remedy for this is to start the vehicle in park and then immediately shift to neutral. This will fill the converter which gives a quicker vehicle response.The block diagram (1) has the converter and pump shaded to show they are the only units in operation. In park, the driveline will be locked as explained above.Drive BreakawayDrive breakaway (or low gear) is used to move the vehicle from a dead stop or very slow roll.When the shift lever is placed in drive, the rear clutch drive plates rotate the front annulus gear pinions which then spin the sun gear in a reverse direction. The sun gear then rotates the pinion gears of the rear planetary in the same direction as the engine which gives a 2.45:1 gear reduction. The rear planet carrier is splined to the low-reverse drum which is held stationary by the over running clutch. The rear annulus gear is locked to the output shaft, so when the rear planets are rotating, the output shaft is spinning. Reviewing the mechanics of this again will show that the planet pinions of both planetaries transfer the torque from the input shaft to the output shaft. As the input shaft turns 2.45 times, the output shaft turns once.In drive breakaway, the rear clutch is applied and line pressure is directed to various valves in the valve body. The same oil is also present at the governor and the signal is modulated and returned to the valve body to prepare for the 1-2 shift.Manual Low, Drive Second or Manual SecondWhen the selector lever is placed in the low gear position something else is needed to supplement the existing Drive Breakaway units. Manual low is used to slow the vehicle down when the vehicle is in motion or to hold the transmission in low gear longer than the governor and throttle pressure circuit normally allow. Engine braking (the slowing of the vehicle) is accomplished by using the low-reverse servo to apply the low-reverse band around the drum. When the vehicle is stationary, the over-running clutch will hold the drum, but when the vehicle is already out of low gear, the drum is free wheeling and can only be stopped by the low-reverse band. (Low gear is a combination of the front and rear planetary sets, so the low-reverse drum has to be stationary to hold the rear planet carrier).It can be seen that manual low is identical to Drive Breakaway with the addition of the low-reverse servo-band assembly and the blocking of the governor signal to the 1-2 shift valve.The Torqueflite is shifted automatically into second gear by a governor signal pushing the 1-2 shift valve over and allowing line pressure to be directed to the front servo-kickdown band assembly and to the accumulator. The governor signal is generated by the rotation of the output shaft which throws the governor weights outward and sets up the proper pre-determined pressure (I'll go into more of the pressure relationships in the modification section). Governor pressure is also directed to the 2-3 valve in preparation for that shift.Since the rear clutch is functioning, and the kickdown band had now been applied, the front clutch drum has now been stopped. The drum is interlocked to the sun gear driving shell with tabs that engage slots in the shell. The rear clutch is still rotating the annulus gear and the sun gear is stopped so no torque is transmitted to the rear planetary. With the sun gear held and the annulus rotating, the planet carrier is spinning at a reduced speed. The planet carrier is splined to the output shaft so it, too, rotates at a reduced speed which is 1 turn for every 1.45 turns of the input shaft.Drive Second or Manual SecondManual second is exactly the same mechanically as Drive second but there is a hydraulic difference. With the lever in second, the vehicle starts in low and shifts to second but line pressure blocks the 2-3 shift valve in the valve body to prevent any 2-3 upshift. The governor pressure will never overcome the line pressure on the 2-3 valve until the transmission is shifted into drive. All the same units are operating when the transmission is downshifted from drive into second. The transmission cannot upshift until the lever is moved back into Drive because the 2-3 shift valve is being blocked by line pressure.Direct DriveWhile the transmission is in second gear, governor pressure is present on the 2-3 shift valve, the front clutch retainer is stopped by the kickdown band, and the rear clutch is applied turning the front planetary and, therefore, the output shaft. When the governor signal moves the 2-3 shift valve, fluid is applied to the release side of the front servo and the front clutch is applied. With the band released, the front clutch starts spinning. Now torque is applied to the front annulus gear by the rear clutch and torque is also applied to the sun gear driving shell by the front clutch (The driving shell is attached to the sun gear). When the sun gear and the front annulus gear spin at the same speed the planet carrier has to rotate at that speed (Gear train rules dictate that when two members of the same gear rotate at the same speed, the whole gear set rotates at that speed). Remember that this planet carrier is splined to the output shaft so it, too, turns at engine speed. Direct Drive is named for the fact that engine speed is transferred directly in a 1:1 ratio through the transmission.Reverse GearWhen the Torqueflite is shifted into reverse a couple of interesting things happen. First the rear clutch, used in all forward gears, is deactivated. Then the front clutch is applied which locks on to the front clutch hub-input shaft assembly. Along with application of the front clutch, fluid is directed to the low-reverse servo which locks the low-reverse band tightly around the low-reverse drum-rear planet carrier assembly. Engine torque can now be transferred through the transmission.Looking at this in order, it happens like this:The front clutch is applied transferring engine torque through the sun gear driving shell, driving the sun gear in the same direction as the engine. With the low-reverse band holding the rear planet carrier stationary, torque is transmitted only through the planet pinions (via the sun gear) driving them in a reverse direction. The only thing left to spin is the rear annulus gear which is splined to the output shaft. Using this planetary only gives one turn to the output shaft for every 2.2 turns of the input shaft, again remembering the output rotates the opposite direction of the input shaft.Hydraulically, there are also a couple of interesting things to note. Governor pressure will not be used in reverse and a quick line pressure check shows reverse to have about 250 + or - 20 psi (where normal line pressure is 75+ or - 19 psi). This is not immediately obvious why reverse should be so high until the rear clutch and front clutch are compared.The rear clutch is on in all forward gears. It uses a Bellevifle spring washer to multiply the piston apply force the necessary amount to transmit engine torque through the rear clutch pack. However, the front clutch has no multiplication factor to depend on when it is applied. Since direct drive is the only other time the front clutch is used and the vehicle is already in motion, no extra holding power is needed to sufficiently lock the front clutch drum. But going into reverse, the vehicle is stationary, and much greater torque (2.2 times as much) will be transmitted through the front clutch plates. Therefore, through a couple of hydraulic tricks, line pressure is almost tripled to give the front clutch the necessary holding power. ................
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