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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

OK, now is the time for the first drive around the block.
A quick run down the street and back, check the fluid one more time. That was the plan anyway. Started going down the street, then waited for a shift, and waited. Backed off the throttle, engine returned to an idle. On the gas again still in first gear. Great, I screwed up the tranny! Turn around and watch the computer monitoring the transmission controller. Take off, shifts 1 to 2 then 2 to 3. At least that is what the computer says. Too bad the transmission isn’t doing any shifting. Back in the driveway. As I am turning it off I realize exactly what I did. Don’t even get out of the truck. Reach down through the hole in the floor left from the NP435 and plug in the wires going to the valve body. Wow, the on screen trans temp now works. Time for another drive.

This time I aim for around the block. It works. Pulls a lot harder now. I had been driving in 2nd gear before thinking it was 1st. Those low gears really pay off. The shifts are late and hard, but it shifts. I get down the road hit the 2 to 3 shift. Again, late and hard. Get up to cruise and it shudders as it goes into 4th. A little more driving confirms everything works. Transmission fluid is a little low, but still on the dipstick.

Then the Crane PS91 coil goes out taking the Unilite module with it. Rebuild the ignition with a good old duraspark and a Jacobs CD box firing a stock coil. Now is the time to take care of the 3 to 4 shudder.

What was happening was that 4th gear (OD) was trying to engage before 3rd gear completely released. When I did the valve body kit I did the 3 spacers on the 3-4 modulator valve. The instructions stated 2 spacers may cause a binding shift (like what I am getting). 3 Spacers may cause a flair (momentary neutral) during the 3-4 shift. I was getting the bind with 3 shims. I had 1 extra spacer left. I decided to put it in and have 4 shims.

That required me to pull the valve body. Unfortunately for me, that is a real pain with the current exhaust. Pull the muffler and the right header pieces out of the way. Then drop the pan. The anti drain back is in the valve body so when you pull the valve body, the torque converter drains on you. Added the 4th spacer to the 3-4 modulator valve and put it together.

Time to try it again. Add fluid again back it out of the driveway. Start to go around the block. Something isn’t right. It feels like there isn’t any line pressure until you rev the engine. There is a shudder as the clutches engage and it starts pulling forward. Damn it! Back it up and pull it in the garage. No reverse. I am revving it as high as about 2200 RPM in reverse, but only have neutral. Fearing a reverse neutral drop if I rev it any higher, I shifted it back into drive and went around the block. The revised shift points I put in while waiting on ignition parts show itself through the slipping. Back into the garage.

Time for a little trouble shooting.
There is enough oil. It did work. The only part I played with was the valve body. Out it comes again. This time I pull the drain plug on the converter, much better. Careful examination shows that the gasket had a minor blemish. NEVER reuse transmission gaskets. Especially when there is a whole stack of them. One stack from the rebuild kit and another stack from the shift kit. New gasket and all is good.

There is a lot of heat coming in through the floor. Maybe I need to cover the hole left from the NP435. A section of not too molested floor comes from Randy at Driven Auto Parts. A Bronco floor to fix a Bronco floor. Self tapping sheet metal screws make it a quick release panel for easy access. A little cut and patch takes care of the relocated transfer case shifter hole. A trip to Wally World net a stout baking tin that covered the hole above the transfer case. Some trimming and some more sheet metal screws and the floor is sealed up.

Let’s put some miles on it. About 100 miles round trip to work, a friend’s house and home. This is in July is Arizona. Trans ran good and cool, about 160°. Probably the only reason it was that warm was that I was warming the fluid through the radiator cooler after the monster F550 cooler. But, the engine was running warm. Around 210 to 215°. That was on a flat level road. It didn’t run hot before the swap to the automatic. Maybe it is that giant tranny cooler blocking airflow. After all, it is larger then radiator.

Pulled the big cooler out and ran just the radiator cooler. Made another 100 mile drive to Hooters and back. Engine temp 185°, trans temp 213°. Time to compromise. Get the largest B&M cooler (about a 1/5 the size of the F550) and try that. I just put that in. Why haven’t I driven it? I had to take care of another problem. Apparently there is a little problem with the AA adapter for the AOD. The seal between the transmission and the transfer case has a tendency to fall out. I have heard of several incidents of this, but AA doesn’t know anything about it. The last drive where I was getting the higher transmission temps probably caused the aluminum bearing retainer to grow a little bit and the seal just fell out. Put a little tranny fluid in the transfer case. Got a new seal and glued it in place. Let’s see how well loctite works.

Another annoying part of the conversion should have been very simple, the shifter. I wish I just got a simple column shifter. But not having one, I did a floor shifter. I didn’t like the standard mega shifter type of floor shifter. While working on getting the shifter the way I wanted it, I did a temporary shift cable. It was real simple. I took an old shift cable, hooked it to the transmission and welded a bolt to the other end. Simple T handle, push and pull. (image 7 below)

I picked up a Unimatic, but didn’t like the feel and got rid of it. What I did get is a Lokar floor mound shifter. (image 8 above) I got a C4 kit instead of the AOD kit. I wanted the correct pattern on the knob. Nice, simple, small, no big bulky cheap looking plastic housings, but not that easy to put in. The kit came with a solid shift rod. There is no way that is going to work. The transfer case just isn’t going allow it. I got a push pull Morse cable 6 feet long with 3 inch stroke. Hooked one end to the transmission and wrapped it around back to the shifter, which is mounted between the seats. The shifter lever is spun 180°, Shelby Cobra style. Had to do some playing to get the stroke of the shifter to match the stoke of the transmission. I still wasn’t done. After all that, the gates in the shifter were not where I wanted them. Lokar likes to lock the shifter in neutral, I don’t like that. I want a stock shifter feel. Maybe I should have used an old Mustang shifter? I had to take the shifter apart and file the shift gate to get the action I wanted. The first time I fixed the flaws I knew I didn’t like. A second trip with a file cut the gates to match the detents on the transmission. Maybe I should have done a Lokar Nostalgic double bend shifter for an AOD and just changed shift knobs instead? Too late now.

I have done a half dozen revisions to the shift tables to get where I am now. Much easier then setting the fuel injection. It took a little work to clean up the early and late shifts and set the line pressure. I had a flair going from 3rd to 4th at light throttle, I though it was the extra shim in the valve body to cure the before mentioned bind shift into 4th. I discovered that I was locking up the torque converter in 3rd. The flair was when the converter unlocked just before the shift to 4th gear. A quick change of software took out the 3rd gear converter lockup, and the flair.

I have only done a little off roading so far. A few hundred incident free street miles and it will ready for a little light trail work. Then we will see how much fun I can have with it. There is a trip to the dragstrip planned soon. It ran a 16.3 weighing 4000 LBS with a bad carb and the NP435. No telling what it will do now with the lower gears, automatic, winch, very heavy bumper, rock skis, fuel injection and larger tires.

Do I like the transmission? Yes. I have dropped about 600 RPM on the freeway, even though I jumped from 4.10s to 4.86 gears. The simplicity of just drive and go is great. Shifts are firm and quick. The adjustability of the transmission controller has allowed me to set the shift points and firmness where I want it.

Would I do it again? Yes.

Did I gain gas mileage? Don’t know. Still playing with it and haven’t checked yet.

Would I have done a different transmission? Probably not. I would liked to have done an E4OD, but the bronco doesn’t have enough wheelbase.

Any thing that I might have done differently? I would liked to have done an Atlas 3.8 instead of reworking to D20. Budget didn’t allow everything.

Costs for the transmission: (not including axles, lift, or the Tera low set):

  • Broken 4R70W: lucky freebie
  • AODE: $350
  • Baumanator: $406
  • Rebuild and valve body: $250?
  • Adapter: $500 ?
  • Starter, flexplate, shifter, cooler, fluid, misc.: $500 ?

I tried to spread the costs out over a long time and I don’t really want to know what I just spent on it.


  • Transmission and other Bronco stuff: Driven Auto Parts
  • Transmission Controller, rebuild parts and a lot of good info: Baumann Engineering (Try the middle of the week, they are often out racing on the weekends. Take Friday and Monday off too)
  • AOD adapter: Advance Adapters
  • Ford engine parts and starter: Towers and Harwood Performance (785)833-6093
  • Flexplate, shifter, hardware, and miscellaneous speed parts: Summit Racing

Tech article by Tim Bowsher (Broncobowsher)

Pages: 1 2 3

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