Jim Smart
August 1, 2009

Ford's C4 Cruise-O-Matic transmission is the most reliable automatic Ford has ever produced. It is simple by design. In fact, it is so simple you can tear it down and rebuild it in your home garage using the Ford Shop Manual because no special tools are required. However, transmission building is a finite science, so we suggest turning yours over to a professional with experience.

We visited Ron Hazelton at Transmission Rebuilding Company (TRC) in Chatsworth, California, which has been in business since 1974. Suffice it to say Ron knows a thing or two about automatic transmissions and has the challenge of keeping up with the latest technology from Detroit, Europe, and Asia.

This is Gary Schweitzer's C4 Dual-Range Cruise-O-Matic transmission, which is suffering mostly from 30 years of storage time. Jaime Sanchez of TRC is going to disassemble and inspect Gary's C4 and give us a report on what it needs. Note the C4's simplicity and compact design. Despite its small size, it is a very rugged transmission.

For this article, we asked Ron to rebuild Gary Schweitzer's C4 Dual-Range Cruise-O-Matic transmission from 5F08T383386, one of 12 convertibles built for the 1965 portion of the New York World's Fair Magic Skyway. Because Gary's transmission had not been operational since 1978, it suffered from the elements in storage. Internally, it was perfect from just 35,000 miles of use.

Jaime Sanchez, a certified transmission tech at TRC, unloaded our C4 and placed it on his bench. Gary's C4 was typical, even with its low mileage. Burned, rancid fluid poured onto the bench, which isn't always as bad as it may seem despite its nasty smell and color. Discolored automatic transmission fluid (brown to black in color) has been hot, laced with friction material from clutches and bands. This means Gary's C4 did its share of slipping in 35,000 miles, burning clutches and bands as it made its way through clutch packs and planetaries. Fortunately, Gary's hard parts survived nicely, ready for a return to service with little more than inspection and resurfacing.

As we knocked down Gary's C4, the wonderful simplicity of this transmission rang true. It is a simple, old-fashioned, three-speed automatic sporting an interchangeable bolt-on aluminum bellhousing, removable tailshaft housing, and main case. The main case didn't change much over this transmission's 22-year production life (including C5 production from '82-'86). Bellhousings and tailshaft housings mainly depended on vehicle application, with Mustangs employing the majority of C4s built.

Jamie Sanchez begins disassembly with bellhousing removal. This is a very snug fit, which called for gentle manipulation with a mallet and large common screwdriver.

C4 Highlights
'64-'66 Known as the C4 Dual-Range Cruise-O-Matic with a very specific transmission selector with a small dot and a large dot (hence the name "Dual-Range"). There has always been a lot of confusion about which dot to use. Use the large dot for normal driving. The small dot keeps it in second gear for driving on icy roads or when a gentle start is required. This version has a 24-spline input shaft (.788-inch) and 24-spline output shaft.

'67-'69 Select-Shift with standard PRND21 selector pattern. Has a 24-spline input shaft (.788-inch) and 24-spline output shaft.

'70 Only Select-Shift with PRND21 pattern with 26-spline input shaft (.839-inch) and 26-spline output shaft. If you're going with the larger 26-spline input shaft in an earlier C4 (prior to 1970), you will need to change the reverse/high clutch drum (forward most clutch), forward clutch cylinder, #3 thrust washer, and front pump.

'71-'81 Select-Shift with PRND21 pattern with 26-spline input shaft (.839-inch) and back to 24-spline output shaft.

'82-'86 Select-Shift C5 is an improved C4 with locking torque converter for better fuel economy. The C5 case is easily identified by casting numbers that begin D2, D3, D4, D5, and D6. The C5 was replaced by the Automatic Overdrive (AOD).

There were two bellhousing sizes for V-8 C4 transmissions - 157-tooth flex plate and 164-tooth flex plate.

There was also a pan-fill C4 designed for trucks with a 164-tooth flex plate. Stay away from these for Mustang applications.

Pinto ('71-'80) and Mustang II ('74-'78) got their own C4 with a smaller bellhousing and 143-tooth flex plate to clear smaller transmission tunnels. They also had a unique valve body.

The intermediate servo on the right hand side is removed first. Because this C4 is for a six cylinder, it has the "Z" servo, the smallest for a C4. Servo size is a matter of piston/bore size and displacement. High-performance applications call for the largest "C" servo, which yields a firmer intermediate band lock-up. The "C" servo is available as a reproduction. TCI Automotive also has a large intermediate servo kit (No. 523005) available for C4 transmissions.

If you're running an '82-up 5.0L engine, you will need a 50-ounce offset balance flex plate or face severe engine vibration.

157-tooth flex plates have a 10.5-inch torque converter bolt pattern while 164-tooth have 11-7/16-inch.

How To Adjust Bands
Intermediate Band Adjustment: Left side of case, tighten to 10 ft. lbs., then back out 1½ turns counterclockwise. The 10 ft. lbs. snugs the band around the drum before backing out 1½ turns. Tighten locknut.

Low-Reverse Band Adjustment: Right side of case, tighten to 10 ft. lbs., then back off three turns counterclockwise.

Torque Converter-How Does It Work?
TRC has the rare distinction of being a transmission shop that rebuilds its own torque converters. Ron Hazelton's son, Troy, specializes in torque converter design and function. Troy walked us through the rebuilding of Gary's factory original torque converter, which needed little more than a good clean up and inspection. It was in perfect mechanical condition.

On the left side, neutral safety switch and kick-down linkage are removed next. We suggest a new neutral safety switch and kick-down cable/linkage from National Parts Depot. The neutral safety switch tends to be a weak link with time and age, causing a no-start condition.

A torque converter does three things: it transfers power from the engine to the transmission's input shaft, multiplies torque to give the engine mechanical advantage, and turns the transmission's front pump to make hydraulic pressure for proper function.

Torque converters consist of five major components - front shell (impeller), stator (hub), turbine (drives the transmission input shaft), rear shell (drives the front pump), and sprag (one-way clutch). The front shell, which contains the impeller, is what gets fluid moving through the converter. The stator is the torque converter's traffic cop. It vectors fluid from the impeller to the turbine, which is splined to the input shaft. The sprag is a one-way clutch located inside the stator, splining it to the transmission's front hub. The sprag's job is to keep the stator locked in position when the torque converter stalls.

Stall speed is when engine rpms are high enough to move the vehicle. As vehicle speed picks up, the stator whirls around with the rest of the torque converter. The stator's primary job is to get us started when the accelerator is pressed. In short, torque multiplication.

This is the low/reverse servo, which controls the low/reverse band and clutch drum. The cover is stamped steel, unlike the intermediate band servo cover on the other side, which is cast aluminum.

Torque converter stall speed should be chosen based on where your engine makes the most power. For stock applications, stall speed should be somewhere around 1,400-1,800 rpm. Weekend racers want to see a higher stall speed around 2,400 rpm, which helps the drag racer get rolling because that's where an engine starts making power. Serious racers want an even higher stall speed around 3,500 rpm. So what does that feel like? When you step on the gas with a high-stall converter, the engine will rev, but not begin to move the vehicle until rpm reaches 3,000-3,500 rpm, which would never be good for the street. Street engines need immediate transmission response right off idle, which calls for a lower stall speed. Street torque converters with low stall speed don't need to be as rugged as racing converters either. Racing converters with higher stall speed need to be rugged, with furnace-brazed fins and heavy-duty components.

Jaime frees up the intermediate band and reverse/high clutch and forward clutch packages, which are the first items to come out through the front. Inside the reverse/high clutch are composition steel and friction clutches along with a clutch piston that engages them under pressure. For proper operation, good friction is needed.

Valve Body
If you're rebuilding a C4 to stock specifications, all your valve body should need is a thorough cleaning and inspection. Valve pistons should be checked for smooth operation-a nice, smooth glide back and forth with no resistance. Springs and check balls should be replaced as necessary. If you desire a firm shift, TCI Automotive has complete performance valve bodies and shift kits. Ask for the #522100 performance valve body.

ApplicationShift Improvement Kit
1965-1966No. 526000
1967-1969No. 526100
1970-UPNo. 526200
When Should Your C4 Upshift?
D1/Minimum Throttle with 3.00:1 or 3.25:1:1-28-10 mph
D1/Maximum Throttle with 3.00:1 or 3.25:11-231-41 mph
D1/Minimum Throttle with 2.{{{80}}}:1 or 2.79:11-29-11 mph
D1/Maximum Throttle with 2.80:1 or 2.79:11-236-44 mph
D1/Minimum Throttle with 3.00:1 or 3.25:12-312-24 mph
D1/Maximum Throttle with 3.00:1 or 3.25:12-354-71 mph
D1/Minimum Throttle with 2.80:1 or 2.79:12-314-25 mph
D1/Maximum Throttle with 2.80:1 or 2.79:12-364-76 mph

Photo Gallery

View Photo Gallery