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.
CHAPTER 3
TROUBLESHOOTING
Troubleshooting is simply finding and fixing a problem. With the TorqueFlite, identifying the problem and knowing where to look for its solution is sometimes tough. This chapter helps focus attention on the internal assemblies and exterior parts that often create common issues.
Like any device designed and assembled by humans, TorqueFlites are not infallible. Over time and with use, their elastomeric materials change due to fluid exposure and heat. Friction materials wear out. Springs change tension. Wear particles from gears and friction materials end up in the wrong places. Driver abuse and neglect take a toll. Eventually, several things combine to cause operational and shifting issues, noises, leaks, and worst case, catastrophic failures.
In 1970, Superbirds stood out because of their long nose and big wing. This brilliant white one retains its original A-727, which was rebuilt in the early 1980s.
Troubleshooting is a bit more difficult now compared to when the TorqueFlites were new because, over time, owners have made “improvements,” swapped parts, enlarged transfer plate holes, and changed springs in the valve body. Many degrade due to storage. Fixing them when they were newer was relatively straightforward; you made sure their parts met the original specifications and you adjusted everything according to factory specifications and engineering changes. Unfortunately, as time passes, original parts are replaced, and original engines and carburetors and the matching throttle pressure linkage, manifolds, and levers are long separated.
Combine several changes and it becomes apparent why it is much more difficult to predict and explain what could be wrong and why it may be tough to find and fix every problem. Unfortunately, (or fortunately, if you have fun doing it) TorqueFlites may simply need to be removed for repair. It is not uncommon to buy a vehicle that has what seems like a simple transmission issue, but that turns into something much more difficult. Often, you just have to return it to its original condition. Knowing the history of the transmission is very important, but many times, it may just not be possible.
In this chapter, information from factory and aftermarket literature is combined with input from experienced mechanics to highlight TorqueFlite operational issues, what could cause them, and what steps can be taken to correct them. Fortunately, because A-904s and A-727s are closely related, troubleshooting is similar.
There are three “Trouble” charts provided in Appendix B: one that deals with troubles that can be diagnosed and fixed with the transmission in the vehicle,