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Discussion Starter · #1 ·
Okay all you AOD experts and enthusiast...I'm thinking about switching out my C4 for an AOD when I put the car back together. A few questions...
1. What are the pros and cons of this type of switch?
2. What do I have to change up and/or swap out to make the change?
3. What are some of the pitfalls I might run into making the switch?

Car currently has a 302 and C4. As much info as possible will be greatly appreciated. :grin2:
 

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1st question- why? I assume everything works as is, so what are you hoping to gain? I went through this the hard way. I swapped out the rear gears for 3:90 and had too high rpm's on the highway. To correct it, I swapped in the AOD thinking it would let the legs stretch a little more. Aside from all the parts needed- crossmember, kick down, exhaust clearance, etc, it was pretty straight forward. The extra gear solved the high end, but the low end is annoying- it's got a goofy quick first shift. I believe there's a kit to help, but it's inherent in the design. If you're looking for a little more oomph, I'd say swap your gears to 3:50's and see how you like it. I guess ultimately it depends on your needs...
 

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two suggestions;

1: get a reprogrammed valve body from either lentech or silver fox. this changes the shift pattern from P-R-N-O/D-3-1 to P-R-N-O/D/3-2-1 so you have full control over second gear. there is an optional o/d lock out if you wish.

2: get the constant pressure valve body option as well so you dont have to get the TV cable adjustment correct to prevent burning up the trans in short order. the benefit of this is that the TV cable becomes the kick down cable.

this swap has been done so many times that there are kits available from various suppliers to help do the job. overall it is pretty straight forward.
 

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1) AOD is heavier, and in stock form, has poor shift quality compared to a lot of other transmission. It does not tolerate hard shifts in 3rd and 4th gears at WOT very well. It will snap the shaft for your mechanical torque converter lockup or burn up clutches if you keep your foot in it at the top end. This can be fixed, but not without removing the torque converter lockup feature. You'd be a lot better off with its younger sibling, the 4R70W, which is the same transmission, but with updated features, and asynchronous shifting. That transmission features a better gear spread, can handle much better power, and shifts great.

2) The AOD requires a mechanical cable linkage for a TV cable, which is usually hooked up to your carb with some fiddly bits. Typically, you will want higher rear gears as well, (3.73+) to take advantage of the overdrive. It will need a new crossmember, and a new driveshaft (preferably a non-steel one, to prevent driveline vibration from the higher RPMs). You will need to do some exhaust work to get around it, because it's wider.

3) Don't put in an AOD. You get overdrive, which is nice for highway driving, but in every other way it's worse than a C4, mugh less the 4R70W. If you want 4 gears, get a V6 4R70W, a controller from Baumann Engineering, and do nothing else to it. If you only drive like a boring elderly woman, you would be fine with an AOD, but if that's the case why swap out the C4 anyway? And why spend big bucks to make an AOD work the way it should (but losing your TC lockup in the process) when you could have all that with a 4R70W, along with the better gearing? Kind of a no-brainer.

As an addendum: the C4 is surprisingly good, if you put in a shift kit. With a hot 302, you can make plenty of tire smoke even with 2.80 rear gears, and run at reasonable highway RPMs on a C4. It may be primitive, but the people who engineered it sure got things right. It's light, it's strong, and it doesn't steal much horsepower. Almost like a throttle-shifted manual transmission. =)
 

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Discussion Starter · #7 ·
1) AOD is heavier, and in stock form, has poor shift quality compared to a lot of other transmission. It does not tolerate hard shifts in 3rd and 4th gears at WOT very well. It will snap the shaft for your mechanical torque converter lockup or burn up clutches if you keep your foot in it at the top end. This can be fixed, but not without removing the torque converter lockup feature. You'd be a lot better off with its younger sibling, the 4R70W, which is the same transmission, but with updated features, and asynchronous shifting. That transmission features a better gear spread, can handle much better power, and shifts great.

2) The AOD requires a mechanical cable linkage for a TV cable, which is usually hooked up to your carb with some fiddly bits. Typically, you will want higher rear gears as well, (3.73+) to take advantage of the overdrive. It will need a new crossmember, and a new driveshaft (preferably a non-steel one, to prevent driveline vibration from the higher RPMs). You will need to do some exhaust work to get around it, because it's wider.

3) Don't put in an AOD. You get overdrive, which is nice for highway driving, but in every other way it's worse than a C4, mugh less the 4R70W. If you want 4 gears, get a V6 4R70W, a controller from Baumann Engineering, and do nothing else to it. If you only drive like a boring elderly woman, you would be fine with an AOD, but if that's the case why swap out the C4 anyway? And why spend big bucks to make an AOD work the way it should (but losing your TC lockup in the process) when you could have all that with a 4R70W, along with the better gearing? Kind of a no-brainer.

As an addendum: the C4 is surprisingly good, if you put in a shift kit. With a hot 302, you can make plenty of tire smoke even with 2.80 rear gears, and run at reasonable highway RPMs on a C4. It may be primitive, but the people who engineered it sure got things right. It's light, it's strong, and it doesn't steal much horsepower. Almost like a throttle-shifted manual transmission. =)
Hey Grim - tell me more abpout the shift kit for the C4.
 

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Ahhh the C4. How I love thee. Let me count the ways...
 
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Well, it's pretty straightforward. A shift kit changes out a few bits in your transmission, allowing hydraulic pressures to rise, or bleed off more rapidly, and engage the servos with more force. Basically, it allows your transmission to shift harder, and slip its friction materials less.

A normal street/strip shift kit will still shift gently and smoothly when you're not on it, but when your foot's in the throttle you'll get hard, tire-barking engagement. This also means that your friction materials will last longer, and your entire transmission will go for many many miles without incident. Sort of "the way it should be" for any performance car.
 

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1) ...
As an addendum: the C4 is surprisingly good, if you put in a shift kit. With a hot 302, you can make plenty of tire smoke even with 2.80 rear gears, and run at reasonable highway RPMs on a C4. It may be primitive, but the people who engineered it sure got things right. It's light, it's strong, and it doesn't steal much horsepower. Almost like a throttle-shifted manual transmission. =)
I have a 289 in my '66 with a C4 with a '67 valve body with shift kit. I replaced the 2 barrel carb years ago with a 4 barrel, Edelbrock intake, and headers. Maybe not "hot" enough, since I've never been able to smoke the tires with the 2.80 gears.

I've since changed the gears with 3.55, but for several reasons haven't been able to drive it yet. I love the C4, but will be looking for someone to replace it with a 4R70W.
 

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^^^ Maybe something else is wrong with your engine because I have been able to burn a tire with the same 2.80:1 gear ratio from stock to modified for 27 years. :shrug:
 
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