1966 Ford Mustang - Project '66 - How To: Performance C4 Buildup

Our Project '66, while encompassing a full restoration, is also tackling the well-worn quest of converting a six-cylinder car to V-8 specs. While we've previously covered suspension, brakes, chassis stiffness, and steering, we're now involved in our drivetrain buildup for our hardtop. Our previously installed Currie Enterprises Super Eight rear fitted with a 3.25 gear and their traction-sensing differential center section will be able to handle our 289's power with ease. But what about what goes between our hotted-up (yet stock-appearing) 289 and our beefed-up (but also stock-appearing) rearend? What we needed for our project was an equally capable, well-built, performance-oriented C4 transmission that retained an outwardly stock appearance, but could handle whatever our 289 could throw at it.

Getting a performance-built C4 isn't something you can usually do with your local transmission shop. Quite often, a stock-level rebuild is the extent of their abilities. We felt the best alternative to our problem was a mail-order transmission for our project car. First and foremost, we didn't have a transmission to rebuild in the first place. Second of all, an experienced performance transmission mail-order company would be able to build what we needed and ship it to our door ready to go (or almost ready, as was our case--more on that in a minute).

After seeing what's out there in the realm of performance C4 transmissions, we chose to work with Dynamic Racing Transmissions. Their level of options, build quality, and quick turnaround were all factors that helped us pick up the phone and call. After discussing our 289's proposed specs, rear gear ratio, tire size, and our intended use of the hardtop with Dynamic's J.R. Miller, he felt our best bet would be one of their fully rollerized Street & Strip C4 transmissions with optional Vasco-Jet input shaft and their solid-strength forward drum. We'll go into these details in the captions, but needless to say, this brute of a C4 will handle all we can throw at it.

Our C4 transmission arrived via truck freight complete and ready for installation. We, however, decided to go the extra length and detail the transmission to look more correct (and fit it with the correct manual lever), as the transmission arrives painted semi-gloss black. The manual lever on the Dynamic C4s is cut off to allow the use of an aftermarket shifter (which follows industry standards). You can add an aftermarket bracket or install a factory lever, which you'll have to procure on your own. But shy of this one concern and the detailing (optional for you non-show types), the transmission will bolt in with no modifications or problems.

Getting the Dynamic C4 to look the part is not a difficult problem. Since the transmission comes completely painted, the surface is already relatively clean. A simple once-over with some form of degreaser to rid the case of any residual assembly oil will suffice before painting. We had good luck with the typical aluminum paints available on the market in spray can form. After masking the output shaft and seal and a few other key areas, we gave the Dynamic C4 three good coats of paint and allowed it to dry overnight. The next day, we broke out the detail brushes and painted the servo covers and attaching bolts, the adjustment bolts, jam nuts, and pan bolts with a natural-finish paint. To finalize your detailing, you can always add the correct paint blotches or stripes, but don't overdo it. If you're not sure what to add, don't put anything on it. You can always go back and add the markings later.

While Dynamic carries several models of C4 transmissions, including their popular Comp, Roller Comp, and Mighty Mite C4s (capable of over 1,000 hp!), we chose their Street & Strip model, simply called the S&S for our project. The S&S C4 will shift for itself fully when in drive and does not require any driver interaction (hence the street part of the name), but it can still be manually shifted for performance (the strip part, naturally). Standard items in the S&S include improved quality clutches and bands, an increase in the number of clutch discs, Teflon sealing rings (for instant sealing without wear), extra-wide babbit bushings, and a recalibrated valve body. All of these standard modifications will increase the durability and life of the C4, while improving shift quality and feel. A nice firm and quick shift is what you will feel with a Dynamic S&S C4.

J.R. cautioned us on one durability area of the Ford C4s design, though. The front pump and support area can be a weak spot when coupled with highway gears (such as a 2.80 or 3.00) due to the amount of torque multiplication required by the transmission. So, upgrade your rear to a 3.55 or better and your C4 will live longer.

We also optioned the Vasco-Jet input shaft on our S&S buildup, as well as the aforementioned solid-strength forward drum and full roller set. Since we've already described the modified drum and full roller set in the main article, we'll discuss the value of the Vasco-Jet shaft here. If you look carefully at the solid-strength drum image in caption 4B, you will see that the splined inner hub has a flat section on each side, often called a blind spline. In a factory C4, the input shaft is splined equally around its circumference, leaving these two areas where there is no contact between the drum and the input shaft. The Dynamic Vasco-Jet shaft, while also stronger than other "hardened" shafts, is machined with a pair of corresponding splines to fit the blind spline areas on the forward drum, giving it 100-percent contact and greater strength--a Dynamic exclusive.