It’s no secret that trucks are built to work hard, and it’s no surprise that parts eventually wear out. Case in point: our 4R70W automatic transmission. With 200,000 miles on the clock, the transmission had a pretty good run, but it was time for an overhaul. Desiring another 200,000 out of a rebuild, we turned to the transmission experts at TCI. What started in 1968 as a shop dedicated to providing high-performance transmission parts to a small group of devout drag racers has grown to be one of the largest and most technologically advanced aftermarket drivetrain companies in the world. So while we could have used the shop down the street, we chose to ship our transmission off and have it not only rebuilt, but also improved. Nothing that leaves the shop at TCI is left stock; the crew only provides performance builds.
Our 4R70W is a great testbed to show just what goes into an automatic transmission rebuild since it was used in such a wide variety of trucks. Ford’s AOD transmission begat the AODE, which then spawned the 4R70W. This transmission was used for 10 years: 1993 to 2003 in the F-150 pickup, 1997 to 2004 in the Expedition, 1996 to 2001 in the Explorer, along with the Mustang, Thunderbird, Cougar, Crown Victoria, and many more Ford applications. From there, it grew into the 4R75W, which lived on in the F-Series until 2008.
Even if you don’t speak Ford, we hope this article gives a brief glimpse into the inner workings of a modern electronically controlled automatic transmission and what it takes to keep it moving down the road. We also hope to give a little insight into building for performance and longevity. There’s no need to scrap a truck when the transmission dies, as a rebuild like this will keep you going for a very long time!
What's a 4R70W?
The 4R70W Ford Overdrive Transmission is an updated version of Ford's long-running AOD transmission that first appeared in the ’80s. The nomenclature breaks down like this:
4 - Four forward speeds
R - Rear-wheel drive
70 - Torque rating x 10 (will hold 700 lb-ft)
Note: This rating is based on torque converter multiplication. It won't stand up to an engine that makes 700 lb-ft at the crank.
W - Wide ratio
Fun Fact: There’s no such thing as a non-W 4R70.
Gear Ratios
First: 2.84:1
Second: 1.63:1
Third: 1.00:1
Fourth: 0.78:1
| 001 Ford 4R70W TCI Automatic Transmission Rebuild
Our 4R70W automatic transmission had a presumed hard life. It spent its days bolted behind a 5.0L V-8 engine, which racked up 200,000 miles. While we didn’t have a catastrophic failure, it was time for it to be gone through. In an effort to get another quarter-million miles from our workhorse transmission, we strapped it to a pallet and shipped it off to the skilled hands at TCI.
| 002 Ford 4R70W TCI Automatic Transmission Rebuild
| 003 Ford 4R70W TCI Automatic Transmission Rebuild
Once the transmission arrived at TCI’s headquarters in Ashland, Mississippi, technician Jeff Reed set to work disassembling the slushbox. First up—removal of the transmission pan followed by the valvebody.
| 004 Ford 4R70W TCI Automatic Transmission Rebuild
| 005 Ford 4R70W TCI Automatic Transmission Rebuild
Next up is the removal of the reverse servo and manual first gear selector, followed by the 3-4 accumulator. When reassembled, a stiffer spring will work to provide increased pressure.
| 006 Ford 4R70W TCI Automatic Transmission Rebuild
Also improved in the valvebody is the overdrive servo. This provides for a firmer 3-4 gear shift and ensures Fourth gear holds solid for many years.
| 007 Ford 4R70W TCI Automatic Transmission Rebuild
| 008 Ford 4R70W TCI Automatic Transmission Rebuild
With work to the valvebody and servos complete, the next step is to move on to the fun stuff, beginning with removing the pump housing from the transmission body.
| 009 Ford 4R70W TCI Automatic Transmission Rebuild
One of the most important parts of any automatic transmission is the oil pump. High-pressure fluid is what enables shifting and holds gears, so having a perfectly functioning pump is absolutely crucial. TCI went to task with replacing the pump gears, along with truing the pump face on a surface grinder.
| 010 Ford 4R70W TCI Automatic Transmission Rebuild
| 011 Ford 4R70W TCI Automatic Transmission Rebuild
Next to come out are the reverse drum and intermediate clutches. This is where we spotted the first signs of heavy wear, as the clutches were badly worn.
| 012 Ford 4R70W TCI Automatic Transmission Rebuild
The folks at TCI replace the intermediate shaft of every 4R70W they build with a high-strength steel unit. This is a common point of failure for these transmissions—and a part you really don’t want breaking.
| 013 Ford 4R70W TCI Automatic Transmission Rebuild
Next out is the forward planetary gear housing. For an increase in holding surface area and friction, TCI squeezes in eight clutch plates in the space that originally held six.
| 014 Ford 4R70W TCI Automatic Transmission Rebuild
| 015 Ford 4R70W TCI Automatic Transmission Rebuild
With the transmission fully disassembled, Jeff cleans all the internal parts, inspects everything, and installs new bushings. Also laid out are all the bolts, nuts, thrust washers, and solenoids.
| 016 Ford 4R70W TCI Automatic Transmission Rebuild
The case also undergoes a rigorous cleaning process during which every bolt hole is inspected for bad threads, every passageway is flushed, and a new case bushing is installed. At this point, the transmission is ready to be reassembled.
| 017 Ford 4R70W TCI Automatic Transmission Rebuild
TCI uses Alto Red Eagle high-performance clutches to ensure an extremely long life. Hard parts are cleaned, inspected, and reused. If any defect is found, the part is replaced.
| 018 Ford 4R70W TCI Automatic Transmission Rebuild
| 019 Ford 4R70W TCI Automatic Transmission Rebuild
| 020 Ford 4R70W TCI Automatic Transmission Rebuild
With the internals back in their proper resting places, the pump and valvebody are both installed and torqued to spec. A fresh filter and gasket round out the rebuild.
| 021 Ford 4R70W TCI Automatic Transmission Rebuild
Every transmission TCI builds runs on the company’s Axiline dyno. This ensures all the critical systems are functional, pressure levels check out, and each unit is completely leak free.
| 022 Ford 4R70W TCI Automatic Transmission Rebuild
Our freshly built 4R70W was returned to us with a new torque converter and fresh coat of paint, ready to slam back into the truck. While this level of rebuild is higher than what most would do, what we have here is something that will keep our truck running for a long, long time.
