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Converting to Automatic

Sminter33

New Member
Joined
Sep 2, 2017
Messages
33
Loc.
Macomb, IL
I may take some heat for this, so take it easy on me...i'm still a newbie haha. I have a 351 in my 75, and when it was put in it was converted to a 4 speed. The EB was originally an automatic. Is it possible to convert back to the automatic? And if so, would that be expensive to do? Thanks for all of you on this board. I've got a ton of good ideas and am currently installing carpet, new roll cage, console, new 15x 10 mags, and chrome bumpers. A lot of those ideas came from this forum!
 

ared77

Contributor
Bronco Guru
Joined
Apr 21, 2013
Messages
2,791
Hey Sminter33, I'm kind of a rookie on EB's too, but I do know it can be done. And I'd also like to convert one of mine to automatic. I'm not sure about expense but I'd imagine it can really vary. For example, if you had an EB owner who lived nearby and wanted a 4 speed instead of his automatic. You could agree to work on each others Bronco's swapping the two transmissions and keep the cost down. Or on the other extreme, drop off your '75 at a shop and have them do a complete change to automatic a very expensive way to go I'd imagine.

What I'd like to have is a list of what all would be required to make the standard to auto. swap. Someone on here may have some sort of check list like that that they will share with us.
 

Galt72

Contributor
Newbie
Joined
Apr 21, 2004
Messages
617
If your going to go through all the trouble then take a look at the 4 speed autos like the aod and the 4r70w. You can put a lot of 4r70w parts in the aod if you don't want computer controlled. They are probably easier to find than a bronco specific C4 these days.
 

PaveBronco

Sr. Member
Joined
Oct 30, 2012
Messages
912
Did mine about 4 years ago, only cost me gas money, pulled my whole 4 speed setup, clutch pedal, flywheel, starter...everything, and found a CB member who wanted to swap his automatic set up for mine. We both drove, met in the middle TX to Tennessee. Mine 71 was and auto at one point, or maybe just had the auto column, so that made it a bit easier.
So I say throw it out on the CB classifieds, see what you get back. What kind of 4 speed you have?
 

904Bronco

Contributor
Bronco Guru
Joined
Sep 28, 2004
Messages
5,749
Loc.
San Martin, CA
Short answer is yes it can be done.

The ^^^ recommendations are great, do a swap with someone.

If your are going to do it, switching to a 4-spd Auto would be good, but there will be an added cost because of the AA adapter needed, a possible rebuild and a controller if a 4R70W is chosen... The T-case shifter moves back 1.5 inches, cross member needs mods, and you might have to shorten/length drive shafts.
 

englewoodcowboy

Lick Creek Restorations
Joined
Jul 25, 2010
Messages
4,200
All good ideas but when you go 4 speed auto or add overdrive, you will push the spend a bit further with needing to regear it to take full advantage of everything. As for mixing 4R70W parts into an AOD, it is not entirely necessary. We are not building drag cars so you have to take the mindset of that as well as the mindset of those who will argue the gear ratio is better in the 4R, well if built correctly I seriously doubt anyone would ever know the difference since the ratios are so close in the first place. I am not knocking the idea of upgrading it but it really is not necessary for most of the average use these days of street and mild trail.
 
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KeithKinPhx

Sr. Member
Joined
Jan 8, 2017
Messages
444
I am currently swapping out a manual 3 on the tree for the automatic 4 speed(4r70w). Bought everything from BC Broncos and they are walking me thru it step by step. Not sure I would have tried without Jason agreeing to answer my dumb questions. It was nice to have everything arrive on one pallet.
It has been relatively expensive since I am replacing steering column and radiator too. I figure the truck is 50 years old and I am getting it ready for the next 50.

Good luck. I've been dropping videos on YouTube under Rising Phoenix Bronco.
 

73azbronco

Contributor
Bronco Guru
Joined
Nov 11, 2007
Messages
7,796
Why 4r70, Anyone considered a 6r80 or 10r80? These things can take the HP and are behind 4x4's. They have computers and kits to boot.
 

KeithKinPhx

Sr. Member
Joined
Jan 8, 2017
Messages
444
4r70w has the same lower three gear ratios as the stock 3 speed manual with the fourth acting las the over drive. This maintains off road performance. The tranny is widely available so parts and service are not an issue. Adapter kits readily available.

The big one is physical size. To do the install you only need a 1" body lift and a modified cross member.
 

bronconut73

Bronco Guru
Joined
Aug 7, 2012
Messages
9,916
Everyone talks about how the 4R70W has a better 1,2,3, gearset than the C4. I think the AOD has the same 1,2,3, gearset as the C4 but of course both with OD.
The AOD was the old "stand-by" overdrive tranny but the 4R70W was just so much better stronger almost everybody has walked away from the AOD.
 

69broncofun

Bronco Guru
Joined
Nov 22, 2016
Messages
1,380
Sorry dumb question from a novice . Why not just got with a c4 tranny? Seems like it would be less mods to Bronco. ?
 

Broncos n' VWs

Sr. Member
Joined
Nov 6, 2005
Messages
360
I have done the auto swap myself. I have a 75 that was originally an auto (still had the column shifter) and the p.o. had put a 3 speed with a hurst floor shifter in its place. After I had swapped that 3 speed out for a T-18, I drove that for about 4 years and then decided to go with the 4R70W after much thought and hours upon hours reading this forum. Search for the 4R70W threads, especially those where BroncoBowsher has replied... he's a 4R70W guru and he helped me plenty when I did my swap. I would recommend doing the 4R70W swap, because that's all I know and I've been very happy with it. Now... if you are considering that, a couple things to consider and I'm sure you already have looked into this but; tire size and gearing are crucial. 33 inch tires and 4.56 gears are great. I had 33's and 4.56 gears. I went up to a 35 inch tire and the 4.56 is just borderline tolerable. 4.88 or 5.13 with a 35 is a better combo.
You will need to make modifications to your crossmember to accomodate the t-case adapter.
You will also need a controller and TPS signal. I already did the EFI swap with a RJM harness so I had the plug-n-play with the Baumann Controller.
Drive line lengthen for the front and shorter for the rear, as the 4R pushes the t-case back by an inch or so.
You need to fab up or purchase a shifter
I sure if I missed anything, someone else will chime in.
In all reality, finding a C4 setup is easiest (cost and install).
 

Hazegray

Sr. Member
Joined
Aug 10, 2004
Messages
795
Everyone recommends the 4R70W swap, but when I had my AOD built, I ensured top quality parts were installed...that was 10 years ago and it's still going strong! My 351W with 4.11 gears and 33 tires pushes the bronco just fine down the highway 65 - 70 mph.:cool:
 

rguest3

Contributor
Bronco Guru
Joined
Dec 13, 2012
Messages
3,778
Sminter33 - I am doing s C4 swap to a 69 that I am restoring.

I am fortunate that I have a 77 that I am pulling all the original Drivetrain, Kickdown Rod, Steering Column, Auto Radiator and large Power Brake Pedal to complete the conversion into the 69. It will look completely stock and only those here will know it is not original. The C4 and Dana 20 are already rebuild and installed. The 302 will be rebuild in a couple weeks.

It will be a street driven truck and rarely, if ever, see the highway. 265 / 70 / 17s and 4.11 gears should have a comfortable top speed of about 60 MPH with a nice rebuilt 302 with a FiTech EFI. No need for overdrive in this one.
 

sanndmann3

Bronco Guru
Joined
Jun 13, 2007
Messages
1,774
[QUOTE tire size and gearing are crucial. 33 inch tires and 4.56 gears are great. I had 33's and 4.56 gears. I went up to a 35 inch tire and the 4.56 is just borderline tolerable. 4.88 or 5.13 with a 35 is a better combo.[/QUOTE]

x2 on this. I have the 4R70W, NP205, 35" tires and 4.56 gears. changing out to 5.14s over the winter...
 
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