The intermediate band servo size is critical to performance. The 289 high performance V-8 C4 was fitted with the popular "C" servo, which was the largest size available. Shown here are two C4 intermediate servos. On the left is the small "A" servo, common with most C4s. On the right is the "H" servo, which has a large diameter bore and piston to improve band-holding pressure. It just isn't as large as the "C" servo, but it is plentiful and cheap. The C4 has two bands. The intermediate band holds the reverse/high drum, while the low/reverse band holds the low/reverse drum. Believe it or not, the best intermediate band available for the C4 is the original Ford type because it is so durable. Use the best friction materials available for your C4 performance build. Mike's Transmissions suggests dressing the drums before assembly, which improves band hook-up during upshifts.
This is the early C4 transmission case, identifiable by its vent tube. The C8DP part number tells us it is a '68 casting.
When the C4 was first introduced for the '64 model year, it had a smaller, five-bolt bellhousing for the 260/289ci small-blocks of the era. Beginning in 1965, C4s and small-blocks got a larger six-bolt bellhousing pattern to reduce noise, vibration, and harshness. The five-bolt bellhousing is not shown here. What is shown is yet another difference, known as flywheel size. This one will stump you more times than not. Two flexplate (flywheel) sizes were used-157 and 164 tooth. On the right is the smaller 157-tooth flywheel bellhousing. On the left is the larger 164-tooth bellhousing. Most Mustangs had the 157-tooth bellhousing and flywheel.
In the '70s, the C4 transmission case changed, deleting the vent tube and moving the vent to the tailshaft housing.
With the changes made to the main transmission case also came changes to the tailshaft housing. Early C4s, with the vent tube, didn't have a vent on the tailshaft housing (right). When Ford deleted the vent tube, it went to a tailshaft housing vent that looks like a mushroom (left) on top. This vent allows transmission heat to escape.
Here are the two flexplate (flywheel) types. Above is the smaller 157-tooth flexplate. The larger 164-tooth flexplate is pictured below.
Mike's Transmissions in Lancaster, California, has a dust shield designed to fit both the 157-tooth and 164-tooth bellhousings. All you have to do is cut the dust shield for your 164-tooth application. Take a close look where the starter fits, and you will see the perforation for your cut.