The C-4 Transmission

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C4 Highlights
'64-'66 Known as the C4 Dual-Range Cruise-O-Matic with a very specific transmission selector with a small dot and a large dot (hence the name "Dual-Range"). There has always been a lot of confusion about which dot to use. Use the large dot for normal driving. The small dot keeps it in second gear for driving on icy roads or when a gentle start is required. This version has a 24-spline input shaft (.788-inch) and 24-spline output shaft.

'67-'69 Select-Shift with standard PRND21 selector pattern. Has a 24-spline input shaft (.788-inch) and 24-spline output shaft.

'70 Only Select-Shift with PRND21 pattern with 26-spline input shaft (.839-inch) and 26-spline output shaft. If you're going with the larger 26-spline input shaft in an earlier C4 (prior to 1970), you will need to change the reverse/high clutch drum (forward most clutch), forward clutch cylinder, #3 thrust washer, and front pump.

'71-'81 Select-Shift with PRND21 pattern with 26-spline input shaft (.839-inch) and back to 24-spline output shaft.

'82-'86 Select-Shift C5 is an improved C4 with locking torque converter for better fuel economy. The C5 case is easily identified by casting numbers that begin D2, D3, D4, D5, and D6. The C5 was replaced by the Automatic Overdrive (AOD).

There were two bellhousing sizes for V-8 C4 transmissions - 157-tooth flex plate and 164-tooth flex plate.

There was also a pan-fill C4 designed for trucks with a 164-tooth flex plate. Stay away from these for Mustang applications.

Pinto ('71-'80) and Mustang II ('74-'78) got their own C4 with a smaller bellhousing and 143-tooth flex plate to clear smaller transmission tunnels. They also had a unique valve body. If you're running an '82-up 5.0L engine, you will need a 50-ounce offset balance flex plate or face severe engine vibration.

157-tooth flex plates have a 10.5-inch torque converter bolt pattern while 164-tooth have 11-7/16-inch.

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