4R70W Transmission Rebuild - Overhauling a Ford Overdrive Automatic

The joke among guys is if your car is making a strange or irritating noise, turn the radio up. But there are some noises you just shouldn't ignore, and the whine coming from the pump area of the 4R70W transmission in our ex-Santa Barbara County Sheriff's '03 Crown Victoria would surely leave us stranded by the roadside if we took that advice.

We were expecting a bad stator bearing in the torque converter but decided to have the whole trans gone through just to be safe. Good thing, too. It was a mess in there. If you want to see what lots of hard miles do to any transmission, follow along as Leo Glassbrenner, owner of Remac Transmissions in San Dimas, California, builds our severely worn trans to severe duty specs. Chevy and Chrysler guys, read along. Even if you don't speak Ford, there is information in this article that applies to any modern, electronically controlled transmission.

What's A 4R70W?
Basically, it's 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

Gear Ratio Chart
	4R70W	AOD
First	2.84:1	2.40:1
Second	1.63:1	1.47:1
Third	1.00:1	1.00:1
Fourth	0.78:1	0.67:1

Compare the gear ratios and you can see why the 4R earned its W designation. All 4Rs have the same gear ratios, by the way. There is no such thing as a non-W 4R70.

Applications
'93 to '98 Lincoln Mark VIII
'96 to '04 Ford Mustang
'94 to '97 Ford Thunderbird, Mercury Cougar
'95 to '04 Ford Crown Victoria, Mercury Grand Marquis
'93 to '04 Lincoln Town Car
'93 to '03 Ford F-series trucks
'97 to '04 Ford Expedition
'96 to '01 Ford Explorer, Mercury Mountaineer

We pulled the transmission from the car ourselves and dropped it off at Remac. Glassbrenner called us after it had been disassembled to break the news: It was a mess. First of all, the oil pump rotor had worn a deep groove into the pump housing and would need to be replaced.
We pulled the transmission from the car ourselves and dropped it off at Remac. Glassbrenne
The friction discs of the forward clutch were nearly worn smooth.
Second gear had been slipping, as evidenced by the blue spots on the steel rings, indicating that the whole assembly had overheated. In addition, our direct clutches and overdrive band were toast. The seals around the reverse band apply servo were also shot, explaining the annoying driveline shudder when reversing at low speeds.
Second gear had been slipping, as evidenced by the blue spots on the steel rings, indicati

Adding insult to injury, the sealing rings on the tailshaft wore deep grooves in the transmission case. To fix this, we either needed to resleeve the case or junk it for a new one.
Adding insult to injury, the sealing rings on the tailshaft wore deep grooves in the trans
We did discover the source of the mysterious bellhousing noise and were relieved to see that we weren't too far off with our diagnosis. One of the torque converter fins had snapped off and become lodged against the stator.
We did discover the source of the mysterious bellhousing noise and were relieved to see th
That scratching sound coming from the bellhousing was the fin slowly (and imprecisely) machining away our stator.
That scratching sound coming from the bellhousing was the fin slowly (and imprecisely) mac

We were unable to find a usable replacement case for less than $100 by the day we had scheduled for the build, so Glassbrenner decided to resleeve our damaged one. His employee Randy Scott used a special cutting tool to bore out the opening. He then cleaned up the surface with a ball hone on a twist drill.
We were unable to find a usable replacement case for less than $100 by the day we had sche
Glassbrenner prepped the new sleeve with green Loctite 609 retaining compound and tapped it into place with a 3-pound sledge.
Glassbrenner prepped the new sleeve with green Loctite 609 retaining compound and tapped i
Scott then drilled the new sleeve to match the fluid supply and return lines from the valvebody.
Scott then drilled the new sleeve to match the fluid supply and return lines from the valv

He chamfered the holes after drilling.
Glassbrenner told us that during reassembly, you have to pay the most attention to the valvebody components, checking everything for wear. "You must verify the hydraulic integrity in the valvebody. The valvebody is regular aluminum, but the valves are hard anodized [aluminum] or sometimes steel. These electronic transmissions oscillate the valves much more than older transmissions, so there is a lot more potential for wear. All specs need to be spot on." Additionally, we should mention that Glassbrenner, seen here drilling an additional fluid pressure exhaust port in our valvebody, rebuilt our transmission with a Trans-Go shift kit and new parts and a rebuilt torque converter supplied by Tav-O-Matic Transmission parts in El Monte, California.
Glassbrenner told us that during reassembly, you have to pay the most attention to the val
There are a few valves Glassbrenner told us he pays especially close attention to. The first is this solenoid regulator valve that oscillates rapidly in its bore. He replaced it with the new valve in the foreground. Its improved shape fits into and seals the bore better than the stock one. If this valve fails, it can cause a sudden Neutral (i.e., no forward gears).
There are a few valves Glassbrenner told us he pays especially close attention to. The fir

The second is this overdrive servo boost valve, which Glassbrenner replaces in all '01-and-newer 4R70Ws. The original valve is steel (left, upper) and wears out the bore it fits in (left lower), while the new valve (the black one) is anodized and fits into a hardened sleeve. This valve helps control pressure to the overdrive band. When it goes bad, the band will wear excessively, ultimately resulting in the complete loss of overdrive.
The second is this overdrive servo boost valve, which Glassbrenner replaces in all '01-and
The last valve to watch out for is this torque converter clutch lockup bushing. If it goes south, it causes low converter clutch apply pressures and TCC slippage codes. Glassbrenner always replaces this valve. In addition, he replaces all the shift solenoids as good insurance.
The last valve to watch out for is this torque converter clutch lockup bushing. If it goes
The rest of the build is straightforward clutches and seals stuff. Glassbrenner soaks the clutch friction discs in transmission fluid for about 20 minutes before rebuilding, and he lubricates the seals and their mating surfaces with a mixture of automatic transmission fluid and STP engine treatment (in the little coffee can in the photo).
The rest of the build is straightforward clutches and seals stuff. Glassbrenner soaks the

He also verifies that all the seals are holding pressure by blowing compressed air into the fluid passages. You'll be able to hear the pistons apply. If there is no air leaking around the seals, you're good to go. Glassbrenner says, "If it works with air, it will work with fluid."
He also verifies that all the seals are holding pressure by blowing compressed air into th
Be aware that transmission work will require special tools, spring compressors, access to a press, and a good set of snap-ring pliers. Here, Glassbrenner installs the retaining ring to the forward clutch drum.
Be aware that transmission work will require special tools, spring compressors, access to
Also, be sure to lubricate the oil pump rotor and housing. "Don't let it start dry," Glassbrenner warns. That's a good way to burn up all the money it cost to rebuild the trans in the first place.
Also, be sure to lubricate the oil pump rotor and housing. "Don't let it start dry," Glass

Finally, Glassbrenner installed the valvebody, torquing the bolts to 95 in-lb, slapped on the pan, and sent us on our way.
Finally, Glassbrenner installed the valvebody, torquing the bolts to 95 in-lb, slapped on
He gave us a can of cleaning solution to flush out the cooler and lines. You don't want to contaminate your new transmission with trash left behind from your old one.
He gave us a can of cleaning solution to flush out the cooler and lines. You don't want to

AOD vs. 4R70W
While our transmission was strewn out before us on Glassbrenner's bench, he was able to show us the hard part differences among the 4R70W and its predecessors, the AOD and AOD-E. The differences are surprisingly few.

To change the ratios, Ford engineers redesigned the planetary gearset. Note that the 4R70W reverse input shell gear and sun gear (right) are a smaller diameter than the AODs.
To change the ratios, Ford engineers redesigned the planetary gearset. Note that the 4R70W
The smaller sun gear allows for bigger planet gears in the 4R70W carrier (foreground). This accounts for the 4R70W's higher torque load rating.
The smaller sun gear allows for bigger planet gears in the 4R70W carrier (foreground). Thi
Models built after 1998 utilize a mechanical diode in the intermediate clutch, replacing its predecessor's roller clutch. This type of clutch works like a ratchet and is stronger than the springs and ramps of a roller clutch. Unlike a roller clutch, the mechanical diode is not rebuildable and must be replaced if it is not functioning correctly.
Models built after 1998 utilize a mechanical diode in the intermediate clutch, replacing i

There are some other bushing and bearing differences, but think of the 4R70W as an evolution of the AOD. You can rebuild AODs with a 4R70W gearset if you want that transmission's ratios.
There are some other bushing and bearing differences, but think of the 4R70W as an evoluti