Transmission Decision

This is my first classic car and I have no mechanical experience. I’ve owned for the past two years and love tinkering and learning. We’ve done cosmetic stuff like easy electric headlight openers, led dash lights, seats, export brace and the like but nothing major.

Recently I had a transmission place replace the U-joints and bushing as I was getting a clunk when I put it into gear. They also identified a “run-up” when going from 1st to 2nd gear (C4). I felt that but didn’t know what it was called. Anyway, the choice is have the C4 rebuilt, or, upgrade to a better transmission (something with more gears for hwy would be preferable).

This is my daily driver so I would like it to run well. The shop has estimated roughly $1500 for rebuild (1 yr warrantY) and $3000 for a four speed with overdrive (2 yr warranty). They said they can put in a replacement that will require some electronics and shortening of the drive shaft making it effectively a 4 speed transmission with automatic overdrive (effectively a 5 speed I think).

So my question is, what are most Cougar owners doing as a transmission upgrade (not for performance but for comfort and fuel economy) and are there any things to avoid? Also, are these costs relatively in-line for a shop that has a good reputation? The car’s not exhibiting any other issues so I’ll probably wait until other symptoms arise. It is my daily driver so I don’t want to wait too long.

Any and all advice, experience or criticism :slight_smile: is welcome!!!


AOD is a common OD AT upgrade and it requires no electronics (AODE which is the next generation does).

I like jamming gears so I would put in a T56… but that’s me. AOD is a good option.

I third the AOD trans. It’s a 4 speed auto built on the same platform as the C-4. Most parts even interchange. Around here, you can get a Used AOD for $200 or less, and they can be rebuilt for about $700 here. That’s a stock rebuild of course. Without changing rear gears you’ll probably see a 4-5 mpg difference on the highway. The AOD came in 90’s Mustangs, Thunderbirds, And others, I believe they were also an option in the Cougars that decade, offered in the Lincoln TC, continentals, etc. They are very easy to find. On to the other question, the $1500 for a C4 rebuild seams a bit steep for a stock rebuild. I had my C6 rebuilt and modified for high performance for $1250? You can also buy a C4 or AOD from many builders in magazines for less than $1300 for stock applications. So, $3000 seams way steep to me. To me, sounds like they’re trying to sell you an electronic aftermarket TCI or something out of a Chevy?? You can get a HIGHLY modified AOD for $1200-$1900…

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The AOD is bullet proof if built correctly. Give your local recycler a call and ask for a 89-92 Thunderbird or Cougar V8 or Super Charged transmission. This particular unit comes from Ford with all the heavy duty parts and an extra clutch pack, Then find a local shop and have them freshen it up and or rebuild it. The shop will have to shorten the drive shaft and replace or modify the rear cross member. The shifter linkage will have to be modified to work with your Cougar, there are several vendors that offers this upgrade that are reasonable on there prices,

The AOD is what I thought about putting behind the 390 in the truck.
How much HP does the AOD accept before causing issues?

AOD. Where are you located?

BTW, I have a good core AOD trans with converter out of a Fox body Mustang I would like to sell. Located in central NJ.

Thanks for the great info. I’m in Seattle, WA.

$1500 to rebuild a C-4 does sound a bit high, but it’s not unheard-of. $3000 doesn’t sound too far out for a shop to swap in something that wasn’t there. Yes, it’s not a bad swap, but making sure everything functions the way it should takes time.

The AOD is a nice swap. It does add about 25% fuel efficiency on the highway. Around town mpg’s will be about the same. You will need a kick-down cable–Lokar KD2AODHT. Modify your cross member or buy a custom cross member. Being you are going from a C-4, you will need the correct flex plate. An FMX flex plate will work. It is the correct number of teeth, offset and balance weight for an early 302. Usually longer bell housing bolts. The mount is the same. The slip yoke from the C-4 should work. It may have to be cut shorter. Although some AOD output shafts did have splines the full length, some did not. The C-4 driveshaft will work AS LONG AS you do not buy a Lincoln or Econoline AOD. Those versions are 1 inch longer. The standard AOD and C-4 are 30 1/8" overall.
88-92 Mustang 5.0 is a good core the build—that flex plate will not work—it is the wrong balance weight. The 89-ish super charged 3.8 T-bird Super Coupe is best AOD–but hard to find. You don’t need to have all the strongest components that were available since you mentioned you are cruising.

What gear do you have in the rear? The AOD is 33% overdriven in 4th. So, it would turn a 4.11 gear into a 2.75. I prefer to be in the mid 3’s like a 3.50 or 3.73 for cruising with the AOD. you can get by with 3.00:1, but anything smaller is going to lug in 4th.

Yep. You gotta watch your ratios to make sure you don’t have a 4th gear that only engages usefully after 80mph.

In my opinion the C4 is fine and no big deal. You can do 120-125 top speed with one. So, highway use isn’t a big deal. I drove all over the country with my FMX in my car. (cue the “my Cougar has never had the breather off and it does 160!!!” comments)

However, just to be clear, if you don’t have the AOD built properly it’s a real piece of crap. So, you either have one built right or you don’t do it at all.

IMO, I’d just leave the C4 in it and keep everything original. It makes aggressive driving at 75 or so on the highway right in the sweet spot of the engine. But it’s nbd to swap it for an AOD as long as you look before you leap and count all of the costs so you know what you’re in for.

If I had your money and my druthers, I’d convert it to a manual trans and enjoy rowing my own.

The AOD starts pushing factory limits around 400 HP. However with an upgraded clutch, and bands, etc in a rebuild kit, you can safely push them to 500-525 depending on rear gear ratio and ability to hook. Any higher than that and you’ll start needing to replace hard parts, like the input shafts, and drums…

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With a truck, I’d prefer to run an E4OD with a stand alone computer. You have to run an adaptor plate with either trans. My 79 F-350 project will have an E4OD. That is an easy choice as the E4OD was available with the correct bell housing for a 460. Either way, continuous load is much better suited to the bigger parts in an E4OD.

By the way, the AOD is not a C-4 with additional parts, and not much swaps between the two. The AOD is based on the FMX, in style and capacity.

Agreed. E4OD is a better trans for a truck, if you’ve got the $ coin to do it. Much larger, and stronger trans, especially for a 4X4.

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