How To Service Ford Mustang C4 Transmissions
Keep Your Ford Mustang's Cruise-O-Matic/Select-Shift Automatic Healthy With Preventative Maintenance You Can Do Yourself
The C4 three-speed automatic is the most common transmission used in vintage Mustangs. Known as the Cruise-O-Matic from '64-1/2-'66 and Select-Shift from '67-'82, this simple hydraulic slush box, of course, has been passed up by more advanced technology in recent years with overdrive automatics like the AOD, AODE (4R70W), and 5R55W. However, it hasn't been forgotten because nothing beats the C4 for simplicity and dependability if you take care of preventative maintenance.
Produced at Ford's Sharonville, Ohio, transmission plant, the C4 Dual-Range Cruise-O-Matic was introduced at the beginning of the '64 model year. It was described as "Dual Range" because the C4 had two driving modes in those first two years-place the shifter at the "Large Dot" with a detent for normal 1-2-3 upshifts or the "Small Dot" without detent for starting out and driving only in second gear. Beginning in '67, Ford redesigned the C4's valve body for the more common P-R-N-D-2-1 performance. If you needed to start out in second gear on snow and ice, all you had to do was place the selector in "2" and gently apply the throttle instead of wondering where to place the shifter. The dot approach created a lot of confusion and transmission failure because some drivers didn't always know which "dot" (mode) to drive in. Some folks never got out of second gear.
The only maintenance C4 transmissions ever need between rebuilds is clean fluid, a fresh filter, and band adjustment every 30,000 miles or every three years. Sometimes, vacuum modulators and kick-down linkages need adjustment, but rarely. Band adjustment is needed because friction material wears off and the bands stretch from heat and use. Kick-down adjustment is required only if shift programming isn't what it should be. Vacuum modulators virtually never need adjustment except when a new one is installed. Most vacuum modulators last the life of the transmission and never need replacement. They fail when their diaphragms rupture, which sucks transmission fluid into the engine, causing white tailpipe smoke and an unexplained loss of transmission fluid.
In the old days, Ford specified the use of Type F automatic transmission for seal, clutch, and band compatibility in its transmissions. These days, Type F (ESW-M2C33-F) isn't mandatory because Ford stopped specifying its use in 1977 with the advent of more advanced friction materials. As older Ford transmissions have been rebuilt and had clutches and bands replaced, the use of Type F has been less of a concern though it remains desirable. Think of Type F as a stickier fluid, with friction modifiers that provide firm clutch and band engagement, which also means longer service life.
It is generally suggested you use Mercon V synthetic transmission fluid if Type F cannot be found. Mercon V is compatible with all kinds of automatic transmission fluid types according to sources we've consulted. Your transmission fluid's job, aside from the obvious for hydraulic control system function, is to cool and lubricate as it travels throughout your transmission. A C4's moving parts generate a tremendous amount of heat, which is why clean fluid and abundant cooling capacity are so important.
Transmission fluid gets contaminated due to both the environment (dust in the air) and friction materials working inside your C4 transmission. Because C4s generate high temperatures, heat takes a toll on fluid, friction materials, seals, and even hard parts like planetaries, clutch drums, and pistons. This is why having clean fluid and a fresh filter is so important. A C4's filter doesn't filter fluid as finitely as an engine's oil filter for example. It is more like a screen designed to catch particulates and other contaminates that can render your transmission inoperative in short order.
Big Dot, Small DotWhen the C4 was first introduced for '64, it was called the "Dual Range" automatic because it offered two driving ranges-normal 1-2-3 upshift with the selector at the large dot (Drive 1) or strictly second gear while at the small dot (Drive 2). Drive 2 doesn't have a detent like Drive 1 for the flexibility of slipping the shifter down into Drive 1, which does have a detent to prevent accidentally going into First gear unless the T-handle detent release button is depressed. The same can be said for reverse, which is locked out with a detent unless you press the button and move the shifter into Reverse or Park.
Ford did away with the Dual Range feature beginning in '67, which made the C4 easier to understand. Along with a new name for '67-Select-Shift-the later version switched to the more normal P-R-N-D-2-1 pattern.
Throttle and Downshift Cable AdjustmentWe get this question a lot. How do you adjust the throttle and downshift (also known as kick-down) cable on Mustangs with the C4 transmission? Ford, per the Shop Manual, offers the following procedure, reworded here so it's easier to understand.
- Set parking brake.
- Adjust engine idle speed to factory specifications at operating temperature in Drive. Make sure someone is behind the wheel with foot on the brake.
- Throttle must be at idle/stop without choke involvement (warm idle).
- With the engine turned off, check accelerator pedal height from the floor, which should be 4-1/2-inches.
- Again with engine off, disconnect the kick-down cable at the accelerator linkage, which is the adjustable end.
- Have someone depress the accelerator to the floor.
- Adjust cable end so it lines up with the throttle linkage.
- Test drive and check upshifts and downshifts at normal throttle.
- If upshifts occur late or not at all at wide-open throttle, the kick-down cable is too tight. If upshifts occur too early at wide-open throttle, the kickdown cable is too loose.
The kick-down linkage, vacuum modulator, and output shaft governor work together to control upshift and downshift points. Throttle position is what controls both kick-down and vacuum modulation, a fancy term for the amount of intake manifold vacuum and its effect on transmission upshift timing. When there's more throttle, we have less manifold vacuum. When your foot is off the gas, we have high manifold vacuum. The kick-down cable is strictly for aggressive acceleration where a downshift is needed into what many people call "passing gear" (actually Second or First gear, depending on vehicle speed).
Under normal acceleration, 1-2 upshifts in Drive should happen at 17-30 mph; 2-3 upshifts should occur at 32-50 mph.
During deceleration, 3-2 downshift should happen at 33-37 mph, then 2-1 downshift at 19-21 mph. These are broad speed ranges based on the Ford Shop Manual, along with tire size and axle ratio.
At wide-open throttle, 1-2 upshift should occur at 27-41 mph, then 2-3 upshift at 52-74 mph, again based on the Ford Shop Manual, tire size, and axle ratio.
Fluid Servicing FactsAlways use Type F in a C4 transmission (as long as you can find it) and stick with one brand. If you cannot find Type F, go with Mercon V, a synthetic automatic transmission fluid designed to work with all types of automatics and fluids.
With the torque converter and pan empty, the C4 requires eight quarts of fluid. Add five quarts first, then check the dipstick reading with the car on a level surface. With fluid showing on the dipstick at or below the "ADD" mark, start the engine. With the engine at idle, check fluid level, which should be well below the ADD mark. With the engine at operating temperature, check the fluid level again. It should have expanded to the ADD mark. Add fluid one quart at a time until it reaches the FULL mark. It is suggested you not overfill, but instead add until fluid is between the ADD and FULL marks. Take a spin and get your C4 to operating temperature, then check fluid level again. Add fluid to the FULL mark. After an open road drive, examine fluid consistency and color. If it is foamy, the transmission is overfilled. It's always best to underfill, then add as necessary. If you overfill, you will have to either siphon fluid out or loosen the pan. Never check transmission fluid level cold; always check at operating temperature.
Remember, your Mustang's torque converter holds nearly four quarts, or half of the transmission's fluid capacity. If you haven't drained the torque converter, all you will need is approximately four quarts.