Ford C4 Transmission (Complete Guide)

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You are working on a small block Ford Mustang, but it has a C4 transmission. Here’s a complete guide for the Ford C4 transmission.

The Ford C4 was a 3-speed automatic transmission built for Ford inline-six and small block V8s from 1964 - 81. Designed to replace the Ford-O-Matic two-speed units it had been using, the “SelectShift” transmission powered fast cars like the Mustang, Cougar, and Falcon.

The mid-sixties was a turbulent time for the country, but also for American automakers like Ford. Desperate to hold onto the market gains that the company had received from introducing their new line of FE engines, Ford turned their attention to their automatic transmissions. The company knew they could not pair the heavy, cast iron Borg-Warner 2-speed with the new engines due to the excessive weight it would produce. In addition, the 2-speed automatic transmission didn’t have enough heft to transfer power when called on. The company set about to fashion a 3-speed automatic transmission, which they could build in-house for less money and yield better performance. The result of their efforts was the C4 transmission with an aluminum alloy casing that the company quickly married to the new Mustang. The lighter transmission offered customers the added benefit of a second low gear, which made for higher stall speeds and more thrust. So why, to this day, 60 years later, do hot-rodders, restorers, and classic car owners love the C4? Let’s review the C4 transmission to find out some secrets to its popularity.

Table of Contents


Why Did Ford Decide To Develop The C4?

FMC (Ford Motor Company) had been paying Borg-Warner for years to manufacture its 2-speed “Ford-O-Matic” transmissions. The heavy cast iron transmissions were cumbersome, inefficient, and fairly pedestrian regarding speed. The automaker needed high-performance transmissions with less slippage between gears for a generation of hot-rodders who wanted a higher stall speed that could blow the tires off a traffic light. (The GM Powerglide transmission had been around for a while, and GM was experiencing success with it - especially on the racetrack).

The new C4 was much cheaper to make (even with more components). The C4 used the latest technology (Simpson planetary gearset) rather than the twin plate version of the Borg-Warner.

In early versions of the C4 (1964–1969), Ford used a .788-inch 24-spline transmission input shaft and upgraded to a longer 26-spline input shaft (along with a new valve body) in 1970 to produce better thrust. The shift bands were borrowed from Borg-Warner and the friction plates were made with highly efficient and heat-resistant metals, and a front pump kept the fluid flowing to power the torque converter and the transmission clutches. The torque multiplication was huge, and a high stall converter helped raise the torque on the start line.

One of the ways to solve the weight problem and ensure that FMC vehicles could outrun the competition was to fashion a three-piece valve body housing made from aluminum alloy. The weight lightened to around 130 lbs, and while nothing beats cast iron, the new metal proved very durable. As a bonus, it improved gas mileage.

In the early years, the Ford C4 automatic transmission was a function that was optional on most vehicles across the small engine lineup. It was a part of some notable brands on the Ford, Mercury, and Lincoln lineups, including the ‘65 - ‘81 Mustang, ‘68 - ‘81 Thunderbird, ‘72 - ‘81 Mercury Capri, ‘65 - ‘82 F-Series, ‘67- ‘81 Mercury Cougar, as well as many others.

What are the Gear Ratios of the C4?

First Gear Second Gear Third Gear Reverse
2.46:1 1.46:1 1.00:1 2.00:1

Where Was the C4 Transmission Made?

The C4 was produced for its entire lifetime production cycle at the Sharonville transmission plant in Ohio, where it continued to be made until the C4 was discontinued in 1981. Ford used the Sharonville plant to produce the C6 automatic transmissions designed to fit their high-performance big-block V8s.

What Are The Specs Of The C4 Transmission?

Item Spec
Weight 130 lbs - (not counting torque converter)
Length 17.0 inches (including bell housing)
Transmission Fluid 8 quarts - (Torque Converter holds 4)
Type of Transmission Fluid F type (Mercon V is fine)
Tailshaft 13 inches (Ford - Merc Cars)
Input Shaft .788 inches (‘64 - ‘69)
Input Shaft .839 inches (‘70)
Bolt Pattern Various (depending on the engine)
Torque Convertor Various (depending on engine)

How Did the C4 Become the SelectShift?

Until this time, Ford had been using outdated Borg-Warner transmissions riddled with poor performance. The company needed to keep consumer confidence up while at the same time, trying to promote the new 3-speed. The company added the words “SelectShift” to the name and quietly promoted its ability for the customer to “select” a low gear. After a couple of years, the name stuck and would be used for the next decade until overdrive transmissions replaced them.

What Are The Problems With the Ford C4 Transmission?

Most weekend racers loved having the new SelectShift transmission because it offered higher stall speed and better rpms making faster takeoffs. Even with its popularity and power, there were some issues that tended to crop up in the engine.

Leaking Fluid

The C4 tended to go through seals and gaskets. Most of the time, the leaking transmission would begin with a drip and slowly increase over time. If left unchecked, the vehicle could lose all the fluid, ruining the components. (A clogged filter often kept the fluid moving through the small transmission. If the filter needed to be replaced, it could be done in a home garage. The tailshaft housing can also be leaking).

Clutch Failure

Many C4s tended to wobble a bit as they were shifting gears. The forward clutch often failed due to a loss of hydraulic pressure. In most applications, the clutch failure would require a transmission rebuild with completely new components.

Band Slippage - The Death Shudder

One of the more severe issues for the C4 was the shudder that happened from the failure of the intermediate band, as the car attempted to move between gears. A clogged filter would interrupt the fluid flow, but the front pump or bad torque converters could also create issues. You may have a transmission issue if the engine wobbles or shudders at a certain vehicle speed. This issue often happens during normal driving, not just when the engine and transmission are under duress.

Is It Easy To Find Parts For The Ford C4 Transmission?

The C4 had a nice long production run that lasted twenty years, so there are plenty of these automatic transmissions on the market today. The components are easy to rebuild, the main case is simple to bolt on, and many older stock torque converters are replaced with aftermarket parts, which are very prevalent. There are many rebuild kits that are available from almost any transmission rebuilding company.

If you are an owner of a Mustang, chances are you have a C4 under the hood, backing up the engine. The C4 automatic transmissions have great rpm range, and are a main reason your beauty is able to push the quarter mile times on the track.