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C4 to AOD swap question

Robster

New Member
Joined
Aug 4, 2015
Messages
36
Will I need to add a body lift kit to help clear the AOD transmission or can I keep the factory body mounts. I have a 2.5" suspension lift but don't really want to do a body lift if I can avoid it. Thanks guys
 

needabronco

Bronco Guru
Joined
Jul 2, 2004
Messages
6,411
Loc.
Prescott/Farmington
You don't need a body lift for an AOD. A 1" helps but is not needed. You will need to modify the crossmember and move it back a little bit, but that's really a 15 minute job with a cut off wheel and a welder. You will need to re-gear your axles and you 'might' need to shorten your driveshaft? I did a 3.5" lift and an AOD at the same time and I didn't need to change my drive shaft out.
 
OP
OP
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Robster

New Member
Joined
Aug 4, 2015
Messages
36
.

Do u have a picture of what needs to be done to the cross member? Is there any frame modification that need to be made? Thanks
 

Tulsa76bronco

Sr. Member
Joined
Apr 23, 2013
Messages
584
That’s exactly what I am doing I have a 302wiyh an aod and have been wanting to get my gears changed that’s what I’m going with
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
You will probably want a lot more gear with those tires and the overdrive in the AOD. 5.13s come to mind. Still have a 302?

This advise comes from someone who has run 4.88s with 33s and a 4R70W behind a 351W built for torque. Your planned 4.56 gears you can expect gear hunting on every hill, and gear hunting in and out of OD is what kills an AOD.
 

Tulsa76bronco

Sr. Member
Joined
Apr 23, 2013
Messages
584
In my situation I will just be riding it around town and an occasional highway 98%of the time
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
In my situation I will just be riding it around town and an occasional highway 98%of the time

Yea, that is where the 5.13s would be really good. Strange to think of 5.13 as a good highway gear, but they would be. Comes to an effective 3.42 gear with the AOD. And the AOD has a locked convertor in OD, so no fudging a little slip, its locked like a stick shift would be. Now 3.42 gears and 35" tires, that's still pretty tall geared. I can remember my first bronco running around with only 31s on it and 3.50 gears. And I know I was pushing a lot less air then you will be, you have a lift and taller tires I didn't have.

If you have 3.50 gears and a C4 already, 5.13s will be even less RPM. Geared a little taller, and a locked convertor.

You need enough gear that at cruising speed you are still pulling some manifold vacuum. If you are not pulling vacuum at cruise the engine is running a peak torque (at that RPM), you have no reserve capacity to pull a grade or accelerate, fuel and timing will be in "power" delivery and not "economy" mode.
 

Tulsa76bronco

Sr. Member
Joined
Apr 23, 2013
Messages
584
I mis spoke my bronco with the AOD has 33inch tires and I am putting in the 4.56 gears what’s ur thought on that

%) that’s what happens when u have two EBs can’t keep them straight othe is 302 w C4 but was still going with 4.56....thoughts
 

Tulsa76bronco

Sr. Member
Joined
Apr 23, 2013
Messages
584
both have 302 engines
C4 had 35 tires 3.5 lift 1 inch body
AOD has 33 tires 2.5 lift 1 inch body
 

Nothing Special

Sr. Member
Joined
Nov 25, 2016
Messages
804
I'll represent the other view. For a while I had an AOD with a manual valve body and a non-lock-up torque converter (yes I know now that was a bad idea) with 4.10 gears and 33" tires. I actually really liked the gearing. (I still have the 4.10 / 33s but now with an NV3550). Yes it needed to be downshifted to pull hills, but the flat cruising was great for what I want anyway. With the manual valve body mine didn't hunt obviously, but manually taking it out of overdrive when needed works too.

But yes, if you want to stick it in "OD" and not think about it, the 4.10s were way too tall.
 

chriskent85

Full Member
Joined
Aug 17, 2016
Messages
293
Not trying to highjack the tread, I plan on running 37's, AOD, 302. which gear ratio would work best for me, its just gonna be a highway driver.
 

Tulsa76bronco

Sr. Member
Joined
Apr 23, 2013
Messages
584
So if I understand this correctly I should do
C4 had 35 tires 3.5 lift 1 inch body...... 4.56
AOD has 33 tires 2.5 lift 1 inch body..... more than a 4.56

I don’t understand what “way too tall” means on gears
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
Tall gears = numerically a low number.

Think of a tall person who only takes a few strides to cover a lot of distance.
Short gears is a small dog whose legs are a blur trying to keep up with the person walking along slowly.
 

Nothing Special

Sr. Member
Joined
Nov 25, 2016
Messages
804
Higher gear ratio equals “Tall gears”

Tall gears = numerically a low number....

... and surprisingly, even though they seem to be saying opposite things, both are correct. "Higher gear ratio" usually is in reference to picking a "higher gear" in the transmission or transfer case, like high range is "higher" than low range. But high range in a Bronco transfer case has a gear ratio of 1:1 while low range has a "higher number" of 2.46:1.

So to be clear people resort to different techniques. Some, like Broncobowsher did, get wordy and specify numerically higher or numerically lower ratios. But a really common way to distinguish is "taller" and "shorter" (or maybe more commonly "deeper"). And Broncbowsher's leg length example is a great way to visualize that. Or you can think about tire size, with taller tires letting the engine go slower at a given vehicle speed
 
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