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Ford Bronco Parts - Classic Vintage Early Bronco Parts

4R70W 4 speed automatic with overdrive

Tech article by admin and filed under - Automatic, Transmission

Tech article by Tim Bowsher (Broncobowsher)

Selecting a new transmission.
It started with when I got the latest Bronco. I didn’t want the old 3 speed anymore. I have heard about the NP435, so I got one. I ran along happily with 33’s, 4.10’s, and the NP435 behind the warmed up 351. It worked ok. The granny was great, but the rest of it was still just a 3 speed. Actually a little slower then the old 3 speed. It really sucked for acceleration.

Rev to the sky. Click. Click. Clunk. Bark. Bog. Repeat.

The crawl ratio was just fine. There could always be more, but it was satisfactory. The clutch chatter was always a problem. Then came the blown D30 front end. Stripped the side gears, chunks took out the ring gear. Driveshaft, U-joints, and finally all the parts fell out of one of the kingpins. The rear posi was not locking like it should.

Came time for a driveline rebuild. Keeping the engine, that runs fine, just need a pan gasket.

I wanted an automatic. That will stop the clutch chatter. I knew I liked the low gears, but would like to get a little better highway cruise. I looked at a lot of options. C4, C6, AOD, E4OD, 700R4, 4L60E, 4L80E, then finally 4R70W. C4 would be an easy swap, but lacked the spectrum of gearing I wanted. C6 was stouter, but same gearing. Looked for something with an overdrive. AOD, It would work, but not the best reputation, put that thought on the back burner. Found AA kit for a 700R4 behind a small block Ford. That looked intriguing. I know that a 700R4 can be built real nice. But then again it is a GM transmission, and the life expectancy is almost nothing. That too hit the back burner.

While killing some time at Driven Auto Parts, I was discussing the options. Why not a 4L80E behind the AA Chevy trans to Ford engine adapter? What about the computer? 4L80E has (at least the option of having factory) a duel stator torque converter. Think of the torque! Ok, time for some more research.

Found transmission computers really expensive when Looking at companies like JET. Overall transmission lengths were getting ugly. Adapters were nonexistent, or rare. Looked at the option of swapping everything. Things looked bad, thought there wasn’t anything on the market that would make me happy. Too expensive, too long, poor gearing, poor history, something was wrong with almost everything.

Then I found a nice transmission controller at a decent price. Baumann Engineering made a nice little controller that solved almost everything. I took a tape measure to an E4OD. With a 20″ long PAN length, I knew that wouldn’t fit under a Bronco. I was pretty much down to the 4R70W. The 2.84 first gear is lower then the AOD/AODE 2.40. The Overdrive at .70 was nice. Not as wide a ratio spread as a 700R4, but it was pretty much a bolt up. Time to start rounding up parts.

Look for a transmission.
Back to Baumann Engineering with the history of upgrades to the AOD/AODE/4R70W line. Sorted through the info and came up with a ’98 or newer V8 Explorer transmission as the perfect base to start with. Soon afterward, Randy at Driven found one. But it had a broken tailshaft and output shaft. That was no problem, I need to replace those parts when I install the adapter. Get it out and find a broken case and a few other wasted parts. But I now have all the upgraded guts and low mileage too. Later I find an AODE from a 3.8L V6 Mustang. Now I have a case, and a spare close ratio gear set in case I ever want to try that.

With the basic ingredients starting to come together I find I still need more before I begin. I order up the transmission controller, specing it out for the digital range sensor. Had a custom made harness that was 4 feet longer then normal at no extra cost, just a little delay in time. That isn’t much of a factor, I have been delaying this for over a year now, mostly because of the new house. A trip to the local Ford dealer got the parts outlined in the AA catalog for making the AOD adapter work for the AODE/4R70W. Oh, I need the AA adapter as well.

Now that I have the big stuff accumulated, I need a few more little things. B&M flexplate, Starter from Towers & Harwood in Manhattan, KS (deal mainly in Ford roundy round racing stuff, aka lots of horsepower and reliable too). Some hardware like flexplate nuts and bolts, Lokar shifter (nice, but a real pain, more later). And a big cooler from an F550.

While collecting parts for the ailing Bronco, I needed to do something about the wasted D30. The answer is obvious, A D44. I wanted it fresh, might as well do it right to begin with. What gears to run? I figured I would start with highway gears and work my way down from there. It is a lot easier to go lower (Terra, cold duck, Marlin, Rock Eaters, Atlas) then it is to go higher (bigger tires, that’s about it).

The current 4.10 gears would come out to about a 2.87 in OD. That was looking a little too tall for tires in the 33 to 35″ range. Looked at 4.56. That came out to about 3.20 in OD. That would be nice on the highway. 4.86 and 5.13 were looked at as well. Those came out to 3.40 and 3.60 respectively.

Then I found Keith Jones from Protofab had a 9″ 31 spline Detroit with 4.86 gears and a D44 housing and a set of 4.89 gears for that. Coughed up the dough and got the bounty. 4.86 gears it will be. Cruise in OD lower the running 3.50 gears. Perfect. Those go under the truck and while I am at it, replace the front springs with some CITI spring from the 2000 Bronco Stampede (only been sitting on those a year and a half). Rears get a set of used 10 leaf Nationals. 2″ block brings up the back to level it. Later a torque arm solves the axle wrap problem. Drove the truck a couple of times with the 435 and 4.86 gears. Wicked. Sucked over 50 MPH.

With the axles ready, time to swap transmissions.
I rebuilt the transmission while waiting on axle parts, so when it was ready as soon as the axles were done. With luck, I had access to a copy of a factory Ford 1997 Expedition service Manual. I copied the 4R70W section and followed it. Out came the front pump, and the rest of the guts. Learned that I needed to mark the location of an anti rattle spring and a snapring. Got the good guts sitting out, time to do it again. Pulled the AODE apart. Set everything aside. Drilled and tapped the vent hole for a remote breather. Washed out the case. The AA instructions suck, but I still managed to get everything back together. While I was at it, I went ahead and replaced the clutches. I didn’t mess with taking the pistons apart, I didn’t have the right tools to put it back together right. Besides, the seals are almost new. Small gamble, but it worked out. All the easy to replace seals got replaced. Carefully assemble the guts in the case and make sure I don’t have any left over parts. A couple of calls to Greg at Baumann Engineering got me all straightened out. The valve body kit went in on the “Moderate” setting with increased torque capacity. After a little though, decided to keep the stock convertor. If I don’t like it, then I have a spare fromt the AODE that I will have reworked later.

Going into this swap I had some concerns about the exhaust clearing the transmission and the transfer case clearing the floorboard.

Then it came the day of no return. After idling into the shop in 4L granny thinking of how much I like this creeper gear. I drained fluids, dropped exhaust, unclipped the fuel injection, and pulled everything out of the way. Got the engine/trans/transfer out in one piece, just like it went in 3 years ago. Set everything on the ground and eyed thing up. Cracked off the old 4 speed and compared it to the auto. The auto was just a little longer then the NP435. Everything looked great. Pulled the slipping clutch to find the input shaft seal on the transmission was leaking gear oil directly onto the disk.

I should mention that the roll of film I burned doing all this didn’t come out, and I am not about to take everything apart just for some pictures.

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