Modified Mustangs & Fords
C4 Transmission Performance Rebuild - Automatic Authority
Mike's Transmissions And Mustang & Fords Show You How To Make The Most Of Small-Block Automatic Transmission Performance
Ford's venerable C4 three-speed automatic debuted in 1964 as Ford's first truly all-Ford designed and built automatic transmission. Prior to that, Borg-Warner did most of Ford's automatic transmissions. There was even a time just after World War II when General Motors provided Hydra-Matic transmissions to Ford.
In the beginning, the C4 was a dual-range automatic transmission, meaning you could drive it in two individual ranges depending on driving conditions. For most of us with '65-'66 Mustangs, that means driving on the little dot or the big dot on the transmission selector-big dot for normal driving and small dot for Second gear only in ice and snow. It didn't take Ford long to figure out this idea didn't work well because not enough people understood it. Some chose to drive on the small dot in error, never leaving Second gear and burning up the transmission.
Beginning in 1967, Ford made the C4 more like other automatics of the period, with a more traditional P-R-N-D-2-1 shifter pattern, ditching the dual-range idea altogether. This made the C4 more user-friendly. From then, the C4 experienced a lot of refinements that made it durable, and it remains the simplest, most reliable Ford automatic ever. Many late-model Mustang racers have come to know the C4 as a terrific automatic transmission for racing, even choosing it over GM's two-speed Power Glide automatic for some racing applications.
In its more than 20-year production life, the C4 was first known as the Cruise-O-Matic and then the Select Shift. In fact, the C4 became the C5 in 1984, sporting a locking torque converter for improved efficiency. It is a hardy, rugged, reliable automatic you can do just about anything with.
C4 - The Differences
As you might expect, the C4 evolved throughout its production life. The first significant change was the valvebody when the dual-range feature was eliminated for 1967. You can install a '67-and-later valvebody in a '64-'66 C4 because the valvebody is the only change. With the valvebody change also came changes (detent positions) in the shifter linkage. These should be addressed when swapping by using the proper indicator.
C4 transmissions prior to 1970 had .788-inch, 24-spline input shafts. In 1970, Ford went to a .839-inch, 26-spline input shaft. This involved a corresponding change in the forward clutch hub, which means you have to change all these components. You can't run a 24-spline input shaft in a 26-spline forward clutch hub or vice-versa.
It really becomes tricky with '71-and-later because the input shaft and forward clutch hub became both 24- and 26-spline. From '71-and-later, the torque-converter end of the shaft is 26-spline and the forward-clutch end is 24-spline. Adding to the confusion, there are a variety of different cases that include case-fill dipstick tubes or pan-fill dipstick tubes. Ideally, you should find a complete '71-and-later C4 transmission with all of the improved components so you won't have to hunt down compatible parts.
Two types of flexplates were used with C4 and C5 transmissions: a 157-tooth and a larger 164-tooth along with a larger bellhousing. With some exceptions, 157-tooth flexplates are used with case-fill dipstick tubes, while 164-tooth use pan-fill dipstick tubes. Pan-fill dipstick tubes are more common prior to 1967.
A rule of thumb for C4 bellhousing identification is those that are 5-7/8-inch deep use 157-tooth flexplates, and those that are 6-1/4-inches deep are the larger 164-tooth flexplate. The C5 is an odd duck with a 164-tooth flexplate and a 7-inch deep bellhousing.
There are many C4 and C5 bellhousing types for a variety of applications. Don't make the mistake of picking up a pump-mount bellhousing for a case-mount C4 and vice-versa. It's easy to make that mistake as these bellhousings look so much alike at first glance. The most obvious difference is 157-tooth versus 164-tooth flexplates. Check depth first, then casting number.
Another important difference is the five-bolt versus six-bolt bellhousing. Small-block Fords prior to the '65 model have five-bolt bellhousings instead of the more common six-bolt pieces from mid-'65 and later. If you're building a 260 or an early 289ci V-8, be mindful of five-bolt versus six-bolt. Five-bolt C4 bellhousings are very hard to find these days.
Because there are endless variables in C4 bellhousings, not all of them are mentioned here, and not all this information is complete. Ford has a time-proven reputation for engineering changes and plucking old part numbers off the shelf in mass production. Expect anything when you go shopping for a bellhousing, including part and casting numbers not mentioned here. And remember, the C4 was used behind fours and sixes as well as V-8s.