In Part 1 of our story on Ford’s AOD-E and 4R70W transmissions, we covered some development history and how to improve some of their shortcomings to make the transmission more durable and capable of connecting real power to the pavement. 

In this article we’ll get into rebuilding a 4R70W. The main thing to remember is assembling an automatic transmission must done in as clean an environment as possible to prevent damage to seals, clutches, ring seals, and hard parts. Dirt and debris will cause big headaches if they get lodged in the tiny passages of the valve body or embedded in the frictions or bands.

The 4R70W isn’t difficult to rebuild if you do it methodically. Take step-by-step pictures during disassembly and lay transmission parts on a clean surface in the order they will go into the case. That will make assembly easier without fumbling and confusion.

Having a shop manual or other reference guide handy can be a big help. One excellent reference is George Reid’s Ford AOD Transmissions book. It has lots of photos of transmission assembly plus specifications and other valuable information.

A couple of other things to keep in mind:
• Soak clutches, bands, seals, rings, and other parts in transmission fluid before installation, and take extreme care to protect those parts during the rebuild.
• Never force parts. If there’s excessive resistance, find out why. Look closely for ragged edges and scoring that can cause resistance. I can promise you that forcing sealing rings and rubber seals will cause transmission failure.
• When you’re stacking clutches, observe proper friction and plate order. Refer to a reference guide like George Reid’s excellent book to confirm check clutch and plate clearances.
• Use compressed air to confirm clutch piston function and check clearances again. Clutch piston function should be snappy when you apply air. The same is true of the band servo function. It must be crisp when you apply air.
• If you point the clutch piston seal lip in the wrong direction (away from the pressure source) it will not hold pressure. The lip must be pointed toward the pressure source in the clutch cylinder so it will seal when pressure is applied. Otherwise the clutch pack will not work because fluid pressure will go right past the seal.

Transmission Rebuilding Company (TRC) in Chatsworth, California has built a lot of transmissions for me. I enlisted their help to reassemble this 4R70W—let’s see how they go about it.

Ford 4R70W reverse clutch drum
Assembly should begin with the gear set. This is the reverse clutch drum. We’re going to load clutches and steels. Many call the reverse drum the “overdrive drum” because the overdrive band wraps around it. (Image/Jim Smart)
Ford 4R70W reverse clutch drum piston
The reverse drum clutch piston installs as shown. The inner and outer seal lips must point toward the inside of the drum. If they are pointed to the outside, it will lose fluid pressure and will not engage the clutches. (Image/Jim Smart)
Ford 4R70W reverse clutch drum clutches and steels
With the clutch piston correctly installed, it is time to install clutches and steels. They go in alternately–steel first, then clutch, then steel, and so on. Repeat until all steels and clutches are installed. This approach increases friction surfaces with multiple clutches. (Image/Jim Smart)
Ford 4R70W reverse clutch drum pressure plate
The clutch pressure plate and snap ring go on last. Always check to make sure the snap ring is secure. (Image/Jim Smart)
Ford 4R70W direct clutch drum
This is the direct clutch. It goes together the same way as the reverse clutch. The clutch drum’s hydraulic piston and seals are first, followed by clutches and steels. The clutch piston and return spring assembly have already been installed. (Image/Jim Smart)
Measuring clutch plates for Ford 4R70W
Steel clutch plates are available in various thicknesses. Check the thickness of each steel and friction-to-steel clearances. (Image/Jim Smart)
Ford 4R70W sealing ring
Sealing rings are made from iron or flexible polymers depending upon where they are located. Take note of the locations of each during disassembly. The iron rings are like piston rings in an engine. Take extra care installing each type so they don’t distort. (Image/Jim Smart)
Ford 4R70W overrunning/one way clutch
This is the sprag, also known as an overrunning or one-way clutch. It allows gearset rotation one way but not the other. Always replace this clutch even if it appears to be in good condition. (Image/Jim Smart)
Ford 4R70W gearset anti-rattle spring
Don’t forget this anti-rattle or anti-clunk spring. It keeps the gearset from “clunking” during upshifts or downshifts. (Image/Jim Smart)
Ford 4R70W intermediate clutches
Intermediate clutches are installed last. The servo piston for these is located in the front pump housing. Clutches and steels go in first, then the pump. (Image/Jim Smart)
Ford 4R70W intermediate clutch servo piston
This is the intermediate clutch, which is an integral part of the gearset and transmission case. Here we are installing the intermediate clutch servo piston, which applies hydraulic pressure to the intermediate clutches and steels. Like the reverse and direct clutches, the seal lip must be pointed toward the inside of the clutch. (Image/Jim Smart)
Ford 4R70W pump/servo sealing rings
These are the pump/servo sealing rings, which are machined iron like piston rings. They are hard yet flexible to provide a leak-tight seal. This ensures proper hydraulic pressure to all of the clutches. (Image/Jim Smart)
Ford 4R70W intermediate clutch return spring ring
With the intermediate clutch piston installed, we are ready to install return spring ring and the retainer ring over the return springs. The pump bushing has been replaced. (Image/Jim Smart)
Ford 4R70W pump stator support
The pump stator support with all sealing rings installed is next. It must be properly torqued to specifications once seated in the case. Always remember to lube the seal for ease of installation. (Image/Jim Smart)
Ford 4R70W low-reverse band servo piston
This is the low-reverse band servo piston. There are three different sizes identified by the number of grooves in the piston. According to AOD book author George Reid, there is a servo piston installer tool (Ford part number T80L-77030-A) that bolts to the case above the servo bore to confirm band torque against the drum. Reid suggests tightening the center bolt to 50 ft-lbs. With a dial indicator positioned at the piston and zeroed, back off the bolt slowly until piston movement stops. The dial indicator reading should be .112-.237-inch. If it isn’t, you need one of three piston types—one groove (2.936 inches), two groove (2.989 inches) or three groove (3.043-inches). The numbers are the measurement from the piston surface to the end of the rod. (Image/Jim Smart)
Installing Ford 4R70W reverse servo piston
Use a humble open/closed-end wrench and a socket for servo piston installation. No need for an expensive installation tool. (Image/Jim Smart)
Ford 4R70W tailshaft bushing installation
One mistake we see from time to time is improper bushing installation. This drain hole must be positioned at six o’clock as shown to ensure proper fluid drainage. (Image/Jim Smart)
Ford 4R70W valve body installation
Valve body installation is straightforward. Photograph each phase of disassembly and lay it out as disassembled to reassemble it properly. Take extra care installing the harness. (Image/Jim Smart)
Ford 4R70W transmission filter
The transmission filter plugs into the valve body as shown. Always change the filter when you do a transmission service. (Image/Jim Smart)
TCI Valve Body Kit for Ford 4R70W
This TCI Trans-Scat Valve Body Kit offers two options–towing or competition shifting. Because these kits eliminate slippage they improve fuel economy, extend clutch and band life, and improves the second to third gear upshift. You can downshift manually or just leave the transmission in Drive. (Image/Jim Smart)
Trans-Go Shift Kit for Ford 4R70W
TransGo pretty much invented the shift improvement kit. Their Performance Shift Kits are available in two versions. The Heavy-Duty kit provides short, firm, full-throttle shifts, holds the gear you select to any RPM, and lets you downshift to any gear. The other converts the transmission to full manual shifting for racing and off-road use. This kit includes a vacuum modulator and eliminates computer-controlled shifting. (Image/Jim Smart)
Remote automatic transmission cooler
Automatic transmissions can operate at fluid temperatures higher than we find in engines. Add an auxiliary transmission cooler if your car is highly modified or you tow a lot. You can never have too much cooling capacity. (Image/Jim Smart)
TCI Max-Shift automatic transmission fluid
Selecting the correct transmission fluid is important. TCI Max Shift Synthetic Transmission Fluid reduces transmission temperatures to help prevent premature wear and reduce internal friction. It’s also kinder to seals, which can harden with time and use. It is suggested you change transmission fluid every 30,000 miles. (Image/Jim Smart)
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Author: Jim Smart

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.