There have been numerous cases on ATSG’s technical hotline where a Ford 500 vehicle came into a shop for repairs requiring the removal of the TF-81SC (AF21) transmission. Once the repairs were completed or the transmission was rebuilt, the transmission did not engage into any gear when it was installed back into the vehicle.
Because the vehicle moved when it came in, a decision to remove the transmission is made. After the completion of an internal inspection, a cause for the no engagement condition is not discovered. The next step that is usually taken is to replace the torque converter. When the unit is re-installed, the transmission still does not engage into any gear.
The cause is the result of the flywheel flexing out of position preventing the torque converter to be engaged into the pump. This flexing out of position occurs as soon as the torque converter was unbolted from the flywheel. Figure 1 compares the height of a flexed flywheel to a new flywheel.
A tip that this might be the reason for the no engagement problem is that the transmission could not receive all the transmission fluid it needs. Because the converter is unable to turn the pump it cannot pick up the fluid. The same problem could occur with a defective filter.
Before installing the repaired or rebuilt transmission, pull the flywheel and place it on a bench. Measure the distance between the converter surface to the bench and from the ring gear to the bench. Compare your numbers to a new flywheel.
A new flywheel measures 1.610 inches from the converter mating surface to the bench and 1.350 inches from the ring gear to the bench.
If your measurements are significantly lower, a new flywheel will be needed (part No. 5F9Z-6375-AA).
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