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
From the January, 2011 issue of Mustang Monthly
By Jim Smart
Photography by Courtesy Ford Motor Company, Jim Smart
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 Dot
When 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.
This is the classic Ford C4...
This is the classic Ford C4 three-speed transmission for six-cylinders and small-block V-8s.
The C4 is a very simple automatic...
The C4 is a very simple automatic consisting of an aluminum case with removable bellhousing, torque converter, engine driven front pump, two multi-disc clutches, two planetaries, an intermediate band, and a low-reverse band along with corresponding servos, output shaft governor, parking pawl mechanism, and a valve body for hydraulic control. The C4 was available in Mustangs from '64-1/2-'82. The more advanced AOD (Automatic Overdrive) arrived in '83.
Transmission service begins...
Transmission service begins with pan removal. The C4 has a very small, 11-bolt steel pan from the factory with barely enough capacity. If you're going racing, you will want more sump capacity along with an external transmission cooler.
With the pan removed, filter...
With the pan removed, filter replacement is easy with a 3/8-inch socket. The filter is nothing more than a screen to keep debris out of the pump, torque converter, and hydraulic system. Fluid is circulated to a radiator fluid-to-coolant cooler where fluid heat is transferred to the radiator, then returned to the transmission.
With the filter removed, a...
With the filter removed, a C4 valve body looks like this. The fluid here is pink, a good sign of excellent transmission health. Brown or black fluid indicates badly burned frictions (clutches and bands) and pending transmission failure. Fluid and filter should be changed every 30,000 miles or every three years depending on how you drive your Mustang.
Service should include washing...
Service should include washing out the pan and inspecting it for warpage that can cause leaks. Reproduction C4 transmission pans are available from National Parts Depot if yours is beyond repair.
Throttle and Downshift Cable Adjustment
We 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.
Pan installation must happen...
Pan installation must happen by the book to prevent leaks. Never use sealer on a transmission pan gasket. Transmission fluid is a thin detergent type that finds its way past every seal and gasket if you're not careful.
Never overtighten pan bolts....
Never overtighten pan bolts. Tighten to torque specifications as directed by the Ford Shop Manual. Overtighten can distort the pan, causing leaks. Use a synthetic gasket, not cork, and evenly tighten the bolts. This is a new reproduction pan from National Parts Depot.
When you change fluid, drain...
When you change fluid, drain the torque converter every other fluid change to avoid shocking transmission seals. Never drain the converter completely. Leave some fluid to keep the front pump primed. Stick with the same brand and type of fluid each time. This is suggested for fluid, friction, and seal compatibility and the sensitive nature of your transmission's hydraulic control system.
Follow Ford's instructions...
Follow Ford's instructions for band adjustment to the letter for optimum results. The tighter you adjust bands, the firmer the shift. However, this is not always advised because everyone has a different opinion of what "tight" is.
This is the low-reverse band...
This is the low-reverse band adjustment located on the right rear side, just ahead of the crossmember. Loosen the locknut, tighten the band 10-12 ft-lbs, then back off the adjustment two full turns. Tighten the locknut. Torquing the adjustment 10-12 ft-lbs seats the band; backing off relaxes the band to proper drum clearance.
Intermediate band adjustment...
Intermediate band adjustment is at the left front portion of the case. Loosen the locknut, tighten adjustment 10-12 ft-lbs, then back off 1 to 1-1/2 turns and retighten the locknut. Adjustments are best performed with a warm transmission.
These are the C4's two bands-...
These are the C4's two bands- low-reverse band is on top with the intermediate band on the bottom. The bands work like clutches, holding and releasing clutch drums. They are activated by hydraulic servos fore and aft in the case.
The C4 was equipped with two...
The C4 was equipped with two basic types of valve bodies-first generation "Dual Range" for '64-'66 and second generation P-R-N-D-2-1 from '67-'82. If you're not concerned about originality, it is suggested you opt for the '67-'82 valve body along with a corresponding change in shifters because detent location is different.
When performing transmission...
When performing transmission service or a complete rebuild, it is suggested you install a B&M shift improvement kit, which is simple to install. The kits firm upshifts, not only for increased performance but also to provide longer transmission life because they reduce or eliminate clutch and band slippage, which creates heat and puts friction material in the fluid to risk damage to the clutch piston seals.
This is the vacuum modulator,...
This is the vacuum modulator, which either screws in or is retained with a clamp depending the C4's vintage. To adjust the vacuum modulator, which controls shift points, remove the vacuum hose and use a small common screwdriver to make adjustments clockwise or counterclockwise, but never more than one-quarter turn at a time. Never go more than four turns in either direction. Clockwise, you increase diaphragm spring pressure, which delays upshifts and makes them firm. Counterclockwise makes shifts softer and earlier. Check the vacuum hose for leaks, which can cause both engine and transmission performance issues.
Here's the neutral safety...
Here's the neutral safety switch and kick-down cable. If you experience a no-start condition and have to cycle the shifter to get a start, the neutral safety switch is to blame and should be either adjusted or replaced.
If your classic Mustang is...
If your classic Mustang is a weekend cruiser or daily driver, a stock steel pan is adequate for both cooling and fluid capacity. If you're going racing or operating in a harsh environment, opt for a deep sump finned aluminum pan (right) for added capacity and improved cooling. Never change fluid without changing the filter.
Typical C4 leakage points...
Typical C4 leakage points are the pan gasket along with front pump and output shaft yoke seals. Whenever you rebuild a C4, make sure these seals get abundant lubrication. Transmission assembly lube is perfect for these seals.
This keeps them pliable for...
This keeps them pliable for dry start-up. What kills seals more than anything is long storage periods followed by dry start-ups. Mixing transmission fluid types can also damage seals. Drive your Mustang at least once a week on the open road to keep everything happy.
Fluid Servicing Facts
Always 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.