Total Torque The Ford C4 Transmission
Total Torque: The Ford C4 Transmission: A guide & Features of the C4, C9 C10.
The Ford C4 transmission, a staple of Ford's automotive heritage since its debut in 1964, symbolizes the Ford’s commitment to ingenuity and performance. Initially designed to replace the dated & awkward Ford-O-Matic, the new C4 Cruise-O-Matic had a lightweight design, enhanced by the aluminium alloy housing. It's often referred to as the C9 or C10, signifying its adaptability with Ford's iconic Windsor and Cleveland engines.
Innovation in Design: The C4 underwent major design changes compared to the Ford-O-Matic. With a calculated division into the bell housing, main case, and tail housing design. The C4 transmission weight was significantly reduced to approximately 185 lbs (83.9 Kg) with an overall length of 20” inches or 51cm long. The new design featured a removable bellhousing, setting it apart from contemporary transmissions of its day. Overall there were two configurations of the C4. The first emerged based on the Windsor platform and had the smaller bellhousing to suit the 157T tooth flexplate. The second design had the allowance to suit the larger Cleveland bellhousing that supported the 164T tooth flexplate, each catering to the 2 various engine types and bolt patterns.
C4 Transmission & how it works: The simplicity behind the Ford C4's hydraulic system—consisting of a torque converter and planetary gear set—ensured a smooth gear shift among its three forward gears and reverse gear. Ford's unique "Select-Shift" system in the early versions underwent a design evolution to simplify gear selection, shifting from the P-R-N-D2-D1-L display to a clearer P-R-N-D-2-1 format in the C4 transmission we know today.
Kickdown Cable: Yes, a C4 transmission requires a kickdown cable. It helps the transmission downshift at full throttle for more power during acceleration.
How much tans fluid does a C4 hold? Typically, a C4 transmission holds between 8 to 10 quarts of transmission oil (7.6L to 10 Liters). This, however this will fluctuate based on specific builds and the pan used and the size of the transmission cooler and the fluid lines.
C4 Vacuum Modulator & the kick down
The C4 transmission, operates off the same basic principle of throttle valve operation, however uses a vacuum modulator to shift. This vacuum modulator is connected to the manifold vacuum port of the manifold and tells the transmission what is going on depending on the load of the engine. High vacuum is low load and low vacuum is a higher load or acceleration. You can fine tune your shift points and transmission behaviour by adjusting this vacuum modulator on the outside of the C4 case.
One full turn clockwise increases control pressure 2-3 psi. One full turn counterclockwise does the opposite. Make your adjustments in small steps (quarter and half turns) and take a test drive and adjust again until your happy.
The Ford C4 has a kickdown linkage that is mechanically connected to the carby throttle lever to the transmission. This lever on the case is connected to the downshift valve within the transmission. The primary throttle position takes its command from the modulator valve (vacuum). However at acceleration or WOT throttle opening situations, there isn't much vacuum to no vacuum, so a mechanical means of throttle position is required. So the kickdown cable or rod tells the C4 trans valve body what is going on and the transmission responds with a down shift or hold in gear.
Compatibility and Performance: The C4 transmission was primarily in Ford's inline six-cylinder engines and the smaller V8s, like the Windsor 302cu (5.0 L). When back in the day, the more powerful engines, such as the 351 Windsor and 351 Cleveland, were typically paired with the FMX or the C6 transmission. The C4 did make occasional appearances alongside the 351M V8s and FE engines.
Throughout its life, the C4 witnessed numerous upgrades. The initial .788-inch 24-spline input shaft of 1964–1969 found in the early Mustangs and suited to the cold and snow areas had a quick shift characteristic from fist to second gear, this was suited to the snowy roads found in North America and Canada. The later design of the .839-inch 26-spline shaft by 1970, further evolving in 1971 and is the common input shaft we see today when purchasing C4 torque converters and transmissions.
Whats the difference between C4, C9 & C10: While the umbrella term commonly used is the C4, it’s crucial to note that two main variants exist and is divided mainly into two categories with a few different names:
- C9 or Case fill or Windsor 157T Small bellhousing: Tailored for Windsor engines, it features a smaller bellhousing with a case fill setup. This C4 transmission is also referred to the Case Fill type. The Bellhousing on this C4 bolts through the front pump and has a smaller hole in the bellhousing.
- C10 or Pan fill or Cleveland 164T Large Bellhousing: Designed for the Cleveland engine, it has a larger bellhousing and a pan fill setup. This C4 transmission is also referred to the Pan Fill type. The Bellhousing on the C10 bolts around the front pump and into the transmission case. The transmission case has a flared flange around the front to accommodate the larger bellhousing.
In Racing & Muslce Car restorations: Its durability and compact size along with the offerings of aftermarket upgrades, make the C4 transmission the best offering among Ford drag racers, Muscle Cars and hot rod enthusiasts as well as other body swaps. Additionally, its resilience, simple design, and ability to handle up to 450 horsepower in stock form (and even more when modified) make it a prime choice for car enthusiasts both in the USA and here in Australia. The C4 Windsor type is sometimes used in Drag racing as the smaller bellhousing allows larger extractor pipes to clear much easier around the bellhousing. Where as some other drag racers prefer the C10 type transmission as the larger front case support of the large bellhousing is seen as a positive. The C10 also has the added benefit of the Pan fill, which allows the racer or enthusiast to have the C4 dipstick located on either side of the transmission, depending on needs.
Conclusion: So, Is the C4 Worth It? Absolutely. The Ford C4 transmission, in all its forms, has demonstrated reliability, adaptability, and simplicity. Whether paired with a Windsor or a Cleveland engine, its consistency and performance have made it an all-time favourite here in Australia. The Ford C4 transmission, encompassing its C9 and C10 distinctions shows Ford's brilliance in automotive engineering. Whether for drag racing, classic car restoration, its compact design, robustness & performance, the C4 transmission remains the go to transmission for the early X series Falcons, GT's, early Mustangs & Capri's.