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.