Calling all AOD gurus: 2wd vs 4wd?

[Crawdad]

I didnt want to hijack a good thread rguest3 started so I wanted to ask it here. While reading the posts I saw where Mattt managed to install a 2wd AOD in his bronco. Am I wrong but I thought you had to get a 4wd version in order for that to work? Is a 2wd the way to go or finding a 4wd the best choice? Or is the 2wd version the same as a 4wd version just with the tail shaft modified internally? Thx for the feedback! Matt

 

[MarkH@Wildhorse]

It does depend on the adapter, there were use to be adapters out there that would change the main shaft, you could then use a 2wd AOD if you had a LATE model.
The adapters we use now, you do not have to worry about the year (it always seemed to be an issue nailing down the year of a tranny) now you just need a 4x4 AOD.

 

[BUCKNBRONK]

I thought the pre 87 years had oiling issues and to stay away from them?.. I uesd one out of a 2wd t-bird, with a AA shaft kit and adapter- worked awsome. But that was 12 years ago dont know what the venders r doing now.

 

[rguest3]

Seems that WH has the Adaptor for the 4x4 version of the AOD. This also works for other transmissions as well as listed on their site.

Advance Adaptors and other vendors sell the 2 wheel Drive Version. (At least I have not seen the 4x4 version there) Not a problem at all if you get the correct Adaptor for the year transmission you have. 88 and newer being the better choice.

I have installed the AOD conversion with the 2wd Adaptor in previous builds with NO problems except the linkage for the transfer case which JB Fab seems to have solved.

Some parts below were not available when I did this before.

Here is what is needed.

Correct Adaptor for certain year 2wd AOD / Or 4x4 Adaptor
Modified Bronco Stock C4 Crossmember
JB Fab AOD Twin Sticks - T-Shift or J-shift
Lokar Column Shift Linkage if using Automatic Steering Column

Should be a pretty straight forward conversion now.

 

[Broncobowsher]

The AOD is internally the same. There are different "tunes" and different level of parts. Things like the pre '87 oiling issues.

As far as 2WD V. 4WD, it is in the tailhousing (external bolt on) and the transmission output shaft (complete trans tear down to replace).

With the AA kit you can start with either transmission. The AA kit has there own proprietary tailhousing and output shaft to work with the D20.
With the BC kit (also sold through countless sources as the ZF adaptor) you need a 4WD transmission. This adapter converts the Bronco D20 transfer case to emulate the standard full size transfer case. So you need a 4WD AOD that will have the output shaft and tailhousing for a full size 4WD transfer case, then sandwich an adaptor between the tailhousing and the transfer case. This way get you an AOD, no trans rebuild is needed (although most AOD will need one by now anyway), and you just bolt up the D20 that fits nicely in the Bronco frame rails. The same adaptor works on other full size transmissions like the ZF (for which it was originally designed), 4R70W, Mazda 5-speed, etc. This adaptor requires a different style transfer case mount and crossmember as it is completely different then the original Bronco style. The AA adaptor uses stock Bronco style transfer case mounts.

 

[mattt]

I'll add my 2 cents & a picture onto what Bbowsher said. First....in addition to the AOD being internally the same across all, I believe it is correct that all of them use the same case, expect for the tail housing and output shaft? With that being the case, they are all 1.5" longer than a Bronco stock drivetrain. That is info to correct what AA has in their tech article for using their adapter in an EB.

I look at it this way in choosing which AOD to use. Pretty much any AOD you find out there on the used market should probably be rebuilt. So.....there really is no reason to go on the hunt for the much less common 4wd version since it has to be opened up for rebuild. To use the AA adapter kit, you have to totally disassemble the trans to install the AA supplied output shaft.

You're either going to disassemble the 4wd or 2wd version to use the AA adapter kit, which includes; aluminum adapter housing, AA specific trans output shaft, AA specific spud input for D20, & various hardware, gaskets, etc.

The ONE main reason other people look harder for the 4wd version is that a full size NP205 transfer case will fit in an EB and will bolt right up to a 4wd AOD w/ no additional adapter. If you want to run a 205, then you are better to find the 4wd AOD. If you want to continue running the stock EB Dana 20 TC, then it really doesn't matter which AOD you start with.

Let me add a sidebar here......you can run the D20 with the ZF adapter on a 4wd AOD also. But, you're still buying an adapter then. What is the price difference between the ZF adapter & the AA adapter? Probably not much. What is the cost difference between the widely available 2wd AOD & the less common 4WD AOD? Enough to probably offset the adapter cost savings?!?!?!? Dunno for sure....

I've attached a picture of a 4wd AOD I used to own. You can clearly see what the Ford factory adapter(for transfer case) looks like in the pic. Everything, case length & internal wise is the same forward of the tail housing. I keep mentioning case length because in the other thread that this sprung from, (having to do with twin sticks), there is some confusion about AOD length which will have an effect on what twin stick will mount to the AA alum. adapter as JBFab intended.

There is one additional difference between AOD 2wd & 4wd. The 4wd has a factory "deep" pan. It's not deep all the way across the pan. It has a deep hump in the middle where the filter pick up snout drops into. That hump makes balancing the AOD on a trans jack during installation a real PITA! Ask me how I know.....not running that pan anymore, now running an alum. deep pan.

 

[Crawdad]

Thx Guys! Very much appreciated! I have a C6 and C4 sitting in storage that are in good running order. Just would like to have that overdrive gear bc I do a lot of driving back and forth to my hunting spot (30 miles one way hwy road) and short trips to my parents 50 miles one way (all interstate). If running skinny 33s on stock gears that may not be all that bad but I sure would like that lower 4.10 or 4.56 gear when pulling a boat. Having an AOD would help bring the RPMs down using those lower gears. I would like to keep the D20 on the C4 but I also have a 205 hooked on the C6. Selling one if not both could help lower the cost of rebuilding an AOD.

Mattt do you have a pic of the TC mods and or tranny cross member?

What is the big diff b/ AOD and AODE? Is one preferred over the other? Which years do I focus on for a donor AOD. I got this link (http://classicbroncos.com/tech/aod-3-speed-automatic-transmission-guide) from mattt earlier this morning on another thread. Says to look for 89 Mustangs on up. Any other models?

 

[Broncobowsher]

The thing when the "E" starts, it is all electronic controls. You need a computer to make it work right. The good thing, you can make it work right. You can dial in shift points. Say everything is shifting great but it is just a little late to shift into OD at very light throttle, you go in and adjust that one little bit and leave everything else alone. Probably the greatest one is the lock up torque convertor. Using an electronically locked convertor you can set it to lock and unlock based on load. It is almost like adding another gear. Set it to unlock before a downshift, you can pickup a little RPM and torque before actually getting into a full downshift. For the most part the 4R70W is the transmission to have. They are still building them new (although I think the Econoline is the last vehicle still using them, the crown vic (taxi and police cars) had them until they quit making them). You can get a later 4WD 4R70W in good condition, use the ZF adaptor and have a good overdrive transmission without taking the transmission pan off. Save the cost of transmission work to cover the computer.