Ford’s 4R70W automatic transmission traces its lineage back to the AOD (Automatic Overdrive) four-speed automatic introduced in 1980. Designed to improve fuel efficiency and reduce engine wear, the original AOD had durability issues, but the big problem was the throttle valve (TV) cable that connected to the throttle linkage to control shift points. That cable was finicky to adjust—If you didn’t get it just right, the transmission would eventually fail.
Ford engineers made continuous improvements to the AOD throughout the 1980s. But the quantum leap came in 1991 when Ford replaced the TV cable with computer-controlled shifting. Thus the AOD-E was born. It provided predictable performance based on factory calibration, vehicle speed, and throttle position. That made the transmission quite reliable.
In 1993 Ford and other automakers revised how transmissions were identified to simplify identification, and the AOD-E was now the 4R70W. The nomenclature breaks down like this:
4 = Four-speed R = Rear wheel drive 70 = Input torque in lbs.-.ft. x 10 (700 lbs.-ft.) W = Wide ratio
The AOD-E and 4R70W use the same main case, valve body, torque converter, front pump, input shaft, and other core components. Both have a Ravigneaux compound planetary gear set. It employs two sun gears and a dual pinion set to allow four forward gears and one reverse. The transmissions have two friction bands, two one-way clutches, and four friction clutches. They also have a true lockup torque converter instead of the original AOD’s ‘split torque’ overdrive lockup feature in third and fourth gear.
The valve body has two computer-controlled shift solenoids and one converter clutch solenoid. It’s made from aluminum instead of steel for improved sealing and reduced weight. Other improvements over the original AOD include stamped steel clutches and a G-rotor front pump that delivers greater fluid volume and pressure at idle.
The main difference between the 4R70W and the AOD-E is gear ratios. The 4R70W has a 2.84:1 first gear and 1.55:1 second gear for improved acceleration. The 0.70:1 overdrive ratio is also more efficient. The AOD-E has a 2.40:1 first, 1.47:1 second, and 0.67:1 overdrive gear ratios.
Like all things mechanical (and electrical), the 4R70W has some drawbacks:
Soft Shifts
One downside of the 4R70W is soft shifts, which lead to wear issues and lost performance. Increasing line pressure and reprogramming the Powertrain Control Module (PCM) will help firm up shifts and prevent clutch and band slippage.
The Sonnax Hydraulic Line Pressure Booster Kit has stiffer pressure regulator springs and large ratio boost valves. This increases line pressure as you lean into the throttle. The springs are approximately 10 percent stronger than OEM but aren’t as stiff as other aftermarket springs.
Direct Clutch
The direct clutch is the 4R70W’s weakest point. Check the cast iron clutch hub for excessive wear and cracking. The direct input shaft/stub shaft will gradually move rearward until it touches the front of the output shaft. That blocks the lubrication feed orifice at the end of the output shaft, starving the planetary bushings and leading to certain gear set failure.
You can also go with an aftermarket direct clutch drum like Sonnax Smart Tech Direct Clutch Drum for improved clutch capacity. The one-piece steel drum has an integrated stub shaft machined from high-strength steel to guarantee there are no splines to strip from the drum or weaken the shaft. Smart-Tech’s drum can hold an OE backing plate and seven OE frictions for 17 percent more clutch capacity than the factory six-friction setup.
Forward Clutch Drum Assembly
The forward clutch drum assembly is another weak spot in the 4R70W. TheSonnax Smart-Tech Forward Clutch Drum from Summit Racing restores proper gear engagement and holding power. Its one-piece forged steel construction makes it much stronger than the stamped steel drum. You also get increased groove depth to provide additional ring support.
Holding power is another issue. Summit Racing offers transmission overhaul kits with heavy-duty clutch frictions and bands that provide additional holding power. These frictions are also good for stock rebuilds as they will last much longer than OEM parts.
4R70W Swaps
Swapping a 4R70W in a classic Ford muscle car or truck uses most of the AOD swap parts like the crossmember, linkages, driveshafts, etc. we’ve long been familiar with.
Because the 4R70W transmission is computer-controlled, you must have a way to control them in a vintage Ford. Holley, MSD, and Performance Automatic offer control modules that let you adjust shift points, torque converter clutch engagement, and select different levels of shift firmness without a PC.
Let’s get into the 4R70W and see what makes it tick.
The electronically controlled AOD-E and 4R70W four-speed automatics introduced in the early 1990s share a main case, valve body, torque converter, front pump, input shaft, and other core components. The main difference between them is the gearset ratios. The 4R70W has a 2.84:1 first gear and 1.55:1 second gear for improved acceleration. (Image/Jim Smart)The AOD-E and 4R70W have a larger input shaft that connects the locking torque converter to the gearsets. They use one input shaft instead of primary and intermediate shafts, which eliminates the smaller lockup shaft as found in the original AOD transmission. (Image/Jim Smart)This is the backup light/neutral safety switch. The output shaft speed sensor is on the left-hand side of the main case. The output shaft speed sensor works with the Power Control Module (PCM) to control shifts based on vehicle speed. (Image/Jim Smart)On the right-hand side of the case is this shift solenoid and torque converter lockup that connects the transmission to the PCM. This connection eliminates the need for a throttle valve cable and mechanical shift modulation. No more messing with a finicky TV cable. (Image/Jim Smart)This is the speedometer speed sensor for an electronic speedometer. If you’re doing a 4R70W swap in a vintage Ford, you may use a speedometer cable drive gear at this location instead of the speedometer sensor. (Image/Jim Smart)The AOD-E and 4R70W manual shift mechanism is the same as the AOD’s except the neutral safety/backup light switch is located outside the case at the manual shifter shaft near the harness. The solenoid controls system line pressure. (Image/Jim Smart)The AOD-E and 4R70W valve body is completely different from the AOD’s. It lacks the throttle valve found in the AOD to control shift programming. The manual shift valve (arrow) has a bolt-on detent not shown here to hold shift selection. (Image/Jim Smart)The AOD-E was originally fitted with a wiring harness that connected the multiplex plug to the two shift control solenoids (black arrow) and the converter lock-up solenoid (white arrow). (Image/Jim Smart)Ford went the AOD-E one better by giving the 4R70W a protective wire channel for the three shift control solenoids. (Image/Jim Smart)This is the AOD-E and 4R70W’s Ravigneaux planetary gearset. What makes the 4R70W better is the wide ratio gearing for improved acceleration. These ratios were chosen to work with the 4.6L Modular V8’s torque curve, which is much different than the Windsor small blocks it replaced. (Image/Jim Smart)The AOD-E and 4R70W transmissions have an improved positive displacement front pump which delivers greater fluid volume and pressure. (Image/Jim Smart)The 4R70W has a deep sump pan for generous fluid content along with a magnet to pick up ferrous metals (steel and iron). It will not catch aluminum and other forms of debris. (Image/Jim Smart)Summit Racing offers complete AOD-E/4R70W transmission kits including this TCI Master Racing Overhaul Kit. It includes performance clutches frictions, and steels; bands; seals; gaskets and bushings; a filter; and a drain plug kit. Most kits don’t include parts like solenoids and other electronics. (Image/Jim Smart)The best life insurance you can give your transmission are premium clutch frictions. Even if you’re building a stocker, opt for high-end, heavy-duty friction clutches and bands. The reward is durability. (Image/Jim Smart)A shift improvement kit increases line pressure, which keeps clutches and bands firmly engaged. Enthusiasts think of shift improvement kits for performance, but they also provide durability. This 4R70W from an F-150 was fitted with a B&M shift kit when the vehicle was new. The transmission got regular fluid and filter changes every 30,000 miles and has been serviced with synthetic fluid. These clutches and overdrive band have 266,000 miles on them and show no wear. (Image/Jim Smart)The AOD-E and 4R70W are equipped with Torrington thrust bearings between gearset segments for reduced internal friction and lost power. (Image/Jim Smart)Most transmission rebuild kits will have these sealing rings. Keep an extra set on hand because they can be damaged during installation. (Image/Jim Smart)The MSD Atomic Transmission Control Module is simple to configure with the supplied hand-held monitor—no PC required. You can adjust shift points, adjust torque converter clutch behavior, select different levels of shift firmness, choose auto-shift or manual shift mode, and activate dyno mode to deliver repeatable chassis dyno results. (Image/Summit Racing)Performance Automatic’s Smart Shift Transmission Controller is another excellent choice. The controller has easy-to-set dials for setting shift points, shift firmness, and torque converter lockup. It also has built-in diagnostic capabilities and indicators to tell you what gear you’re in and whether your torque converter is locked up. (Image/Summit Racing)
Jim Smart is a veteran automotive journalist, technical editor, and historian with hundreds of how-to and feature articles to his credit. Jim's also an enthusiast, and has owned and restored many classic vehicles, including an impressive mix of vintage Ford Mustangs.
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