Ford Motor Company has five basic transmissions that use the Simpson gear train and are quite similar to each other: the C-3, C-4, C-5, C-6, and A4LD. The A4LD is a 4-speed, whereas the others are 3-speeds. All of these units use a gear and crescent-type oil pump as the source of all hydraulic pressures.

The A4LD is a modified version of the C-3. Its housing was enlarged and an additional planetary gearset was added to provide for an overdrive fourth gear. The A4LD was the first electronically controlled Ford automatic transmission.

The gear train for the first three speeds of these transmissions is identical except for the C-6, which uses a low/reverse clutch instead of the low/reverse band used by the other models.

In appearance, these transmissions are similar and all have a separate and removable extension housing. The major external difference between the models is the size and the reinforcements of the case. The bell housings of the C-3, C-4, and C-5 are removable from the transmission case, whereas the bell housing of the C-6 is part of the case's casting.

To control planetary gear action, these transmissions use two multiple-disc clutches, two bands, and one overrunning clutch. The two clutches are referred to as the high, front, or reverse/high and the rear or forward clutches. The two bands are the intermediate, front, or kickdown and low/reverse or rear units. Again the exception to this is the C-6, which uses a clutch in place of a band for low and reverse. See the chart below for the band and clutch application chart for a C-6 transmission.

The power flow through Ford transmissions with a Simpson gear train is similar to that of the power flow through a Chrysler Torqueflite transmission.

Add-On Overdrive The A4LD transmission consists of a torque converter, planetary gear train, three multiple disc clutch packs, three bands, a one-way clutch, and hydraulic control system. The housing of a C-3 was enlarged and an additional planetary gearset was added to provide for an overdrive fourth gear. The additional planetary gearset was added in front of the normal 3-speed Simpson gear train. Input from the torque converter passes through the overdrive planetary gearset before it reaches the Simpson gearset. To control planetary action of the overdrive gearset, the A4LD uses an overdrive band, overdrive clutch, and an overdrive one-way clutch.

The overdrive band holds the overdrive sun gear to provide for fourth gear overdrive. The overdrive clutch locks the overdrive sun gear to the overdrive planetary carrier to provide for engine braking while the transmission is operating in drive. The overdrive one-way roller clutch locks the input from the torque converter's turbine shaft directly to the input shaft of the Simpson gear train and provides direct drive through the planetary gearset by locking the carrier to the ring gear,

Direct drive through the overdrive planetary unit is present whenever the transmission is operating in first, second, third, or reverse gears. During these conditions, all input power flows through the overdrive one-way clutch, also the overdrive clutch is applied to provide for engine braking.

When overdrive is selected, the overdrive band is applied and holds the sun gear. The overdrive clutch is released and the planet carrier becomes the input member driving the ring gear at an overdrive ratio of approximately 0.75:1.