91 GT Convertible AOD Upgrades

DHatton · Jun 7, 2022

Hello,

I'm looking to upgrade my stock AOD Transmission in my 91 Fox Convertible. My engine is stock, but I have some intake and exhaust modifications.

I bought a shift kit from Baumann already, but I want to change the stock gears to a 4.10.

I heard that if you upgrade the gears you should get a higher stall Torque Converter, and I am not sure which stall speed to get, should I get 2400, or 3000 stall? Any companies which make good Torque Converters?

I also need help with choosing a transmission cooler, do you know any companies which sell complete Trans Cooling kits? If not, what parts do I need?

I plan to drive on the street, and in the future I will probably install a supercharger and rebuild the engine for more power.

Thank you.

LAFF · Jun 8, 2022

DHatton said:
Hello,

I'm looking to upgrade my stock AOD Transmission in my 91 Fox Convertible. My engine is stock, but I have some intake and exhaust modifications.

I bought a shift kit from Baumann already, but I want to change the stock gears to a 4.10.

I heard that if you upgrade the gears you should get a higher stall Torque Converter, and I am not sure which stall speed to get, should I get 2400, or 3000 stall? Any companies which make good Torque Converters?

I also need help with choosing a transmission cooler, do you know any companies which sell complete Trans Cooling kits? If not, what parts do I need?

I plan to drive on the street, and in the future I will probably install a supercharger and rebuild the engine for more power.

Thank you.

With today’s gas prices—unless you are a wealthy man—I would go with a 3.08 or close rear end.
With your engine being stock I wouldn’t worry about the transmission.
Not criticizing you or your plans, but I do know what I am talking about.

General karthief · Jun 8, 2022

I'll prolly catch some flack but a 4.10 gear with a basically stock engine is not a good idea, more so if you're planning for a supercharger, the stock cam runs outta steam around 5300-5500 rpms, couple that with a higher stall converter and you'll find the 'fun ' will last about 10',
That said you need a better plan,

Mustang5L5 · Jun 8, 2022

AOD with 4.10's is great for drag racing, but for everyday cruising it's not worth it. You'll find you'll be revving high on the highway and one quirk about the AOD is that Overdrive will not engage over 3/4 throttle (or something in that ballpark), so any freeway passing requires dropping to 3rd gear. For instance if highway travel is 75MPH and you want to pass, that's 4000+RPM in 3rd with the 4.10's. Needless to say your fuel economy will go into the gutter.

4.10's are great for 0-70MPH acceleration, but if you spend a lot of time in the 50-80MPH range on the highway it gets old fast. I had 3.73's with my AOD. Was fun for racing, but I hated them for everyday driving . Felt like i was always revving the hell out of my engine for highway driving and passing.

If you plan on supercharging, i think a 3.27 or 3.55 might be a better option.

LAFF · Jun 8, 2022

Mustang 5L5 is telling you right.
My 1983 is totally rebuilt.
Only thing original is the body and interior.
People around this site know what they are talking about.
Listen to some and tune out the rest.
If you wanna use it as a daily driver you need take that into consideration.
But hey—it’s your money.

General karthief · Jun 8, 2022

@jrichker had a post about planning when building a driver, a miss matched bunch of parts can make it no fun drive. So many things to consider, look around on this site for builds and you'll get the idea.

LAFF · Jun 8, 2022

General karthief said:
@jrichker had a post about planning when building a driver, a miss matched bunch of parts can make it no fun drive. So many things to consider, look around on this site for builds and you'll get the idea.

I can tell the man plenty of to do’s and what not to do’s.

LILCBRA · Jun 8, 2022

I think, if it were me, I'd go with 3.55s and leave the converter alone. But, as far as upgrading the AOD, I'd suggest a spiral lock ring for the front planetary set. The stock snap ring tends to expand at high rpms and let the planetary move forward in the case which ends up grinding into the back of the pump. If you want to get more in depth, which wouldn't be a bad idea if you're planning on adding more power in the future, here's an article on building the "best" AOD.

How to Build the Perfect AOD - AODetail

Ford’s hardy cable-modulated Automatic Overdrive (AOD) was produced from 1980 to 1991, then became an electronically controlled transmission known as the AOD-E

www.motortrend.com

LAFF · Jun 8, 2022

The above is what I was talking about earlier.
Some just wanna tell you how much they think they know.
I have no idea what he was talking about.
Maybe you do.
Gotta think about the $$, and exactly what you wanna have, and you want it to do.

LILCBRA · Jun 8, 2022

The above is speaking from experience with the AOD. When I swapped a 5.0/AOD/8.8 combo from a Lincoln Mark VII into my 84, I found that the front snap ring had let go and the back of the pump was eaten up some. Not enough to cause a failure, but it let debris float around in the oil. Upon research, I found that this is a common problem and the solution was to simply replace the snap ring with a spiral lock ring. The 8.8 I swapped already had the 3.27 gear, so - as I said, if it were me - I'd swap for a 3.55 gear since I've already had experience with the 3.27 ratio. I'm going to guess his car has a 3.08, either or would be a slight upgrade in my opinion, but the 3.55 would be a little more noticeable change from a stop.

LAFF · Jun 8, 2022

LILCBRA said:
The above is speaking from experience with the AOD. When I swapped a 5.0/AOD/8.8 combo from a Lincoln Mark VII into my 84, I found that the front snap ring had let go and the back of the pump was eaten up some. Not enough to cause a failure, but it let debris float around in the oil. Upon research, I found that this is a common problem and the solution was to simply replace the snap ring with a spiral lock ring. The 8.8 I swapped already had the 3.27 gear, so - as I said, if it were me - I'd swap for a 3.55 gear since I've already had experience with the 3.27 ratio. I'm going to guess his car has a 3.08, either or would be a slight upgrade in my opinion, but the 3.55 would be a little more noticeable change from a stop.

I like your explanation.
Wasn’t trying to be a smarta$$.
I took the easy way out when my old C5, or C6 whatever the hell it was, started giving up the ghost behind the engine I put in it—I just bought a new aod.

DHatton · Jun 9, 2022

LAFF said:
With today’s gas prices—unless you are a wealthy man—I would go with a 3.08 or close rear end.
With your engine being stock I wouldn’t worry about the transmission.
Not criticizing you or your plans, but I do know what I am talking about.

Thanks for your response.

Money is not an issue, and I don't drive everyday so I am not too concerned about gas prices.

Could you elaborate about the part where you said that my engine is stock, and I shouldn't worry about my transmission?

DHatton · Jun 9, 2022

General karthief said:
I'll prolly catch some flack but a 4.10 gear with a basically stock engine is not a good idea, more so if you're planning for a supercharger, the stock cam runs outta steam around 5300-5500 rpms, couple that with a higher stall converter and you'll find the 'fun ' will last about 10',
That said you need a better plan,

Thanks for your response.

I don't plan to upgrade my engine/cam, nor add forced induction soon, but I do want to "prep" my transmission and try and make my car as fast as possible in the 0-60 mph range before the added power.

I already purchased the 4.10 gear, and wanted to know whether it is even worth it to add the higher stall converter. If it is, what RPM range for the converter should I look into?

DHatton · Jun 9, 2022

Mustang5L5 said:
AOD with 4.10's is great for drag racing, but for everyday cruising it's not worth it. You'll find you'll be revving high on the highway and one quirk about the AOD is that Overdrive will not engage over 3/4 throttle (or something in that ballpark), so any freeway passing requires dropping to 3rd gear. For instance if highway travel is 75MPH and you want to pass, that's 4000+RPM in 3rd with the 4.10's. Needless to say your fuel economy will go into the gutter.

4.10's are great for 0-70MPH acceleration, but if you spend a lot of time in the 50-80MPH range on the highway it gets old fast. I had 3.73's with my AOD. Was fun for racing, but I hated them for everyday driving . Felt like i was always revving the hell out of my engine for highway driving and passing.

If you plan on supercharging, i think a 3.27 or 3.55 might be a better option.

I drive in London, and sometimes outside London. I usually drive in the street, and don't take the motorway very often.

In the UK the maximum allowable speed is 70 mph on the motorway, but usually on dual carriageways and some motorways you will be driving around 50-60 mph.

In the street I drive between 20-30 mph.

Hence why having a 4.10 isn't too much of a bother for me.

When you had the 4.10 installed, did you use a higher stall torque converter?

Thank you.

Mustang5L5 · Jun 9, 2022

DHatton said:
When you had the 4.10 installed, did you use a higher stall torque converter?

I had 3.73's in my AOD. I never did the torque converter or shift kit. I was actually considering a 4R70W gearset swap along with a torque converter, and then I 5-spd swapped the car.

US speeds are higher, typically 80MPH or so on the highway, which is why I did not like the 3.73;s with the AOD.

JD1964 · Jun 9, 2022

The 93 I just sold had AOD with stock converter and 4,10 rear. I thought it was pretty decent as an all around driver. If your motor is stock or stockish, a higher stall converter really isnt needed in my opinion.

Middleagecrisis · Jun 10, 2022

My '93 GT has an AOD with 3.27 gears. I just installed a new motor with ported GT-40P heads, Lunati Cam and several other engine upgrades. I added an ACC Nightstalker Level 2 torque converter, only because the cam needed the higher stall. I'm staying with the 3.27 gears for now, because of the 80 mph speed limit on our highways and I plan to add nitrous in the future. I haven't rung the motor out yet, because I've only got maybe 100 miles on it so far, but it seems like the 3.27 gears won't be an issue. As mentioned above, a stock motor really doesn't need a higher stall converter. I think you'll find the Bauman shift kit and 4.10's will give you all the benefit the stock motor can provide. Definitely install a plate type trans cooler! You want to keep the fluid cool. Have you done the typical bolt-on upgrades?

DHatton · Jun 10, 2022

Middleagecrisis said:
My '93 GT has an AOD with 3.27 gears. I just installed a new motor with ported GT-40P heads, Lunati Cam and several other engine upgrades. I added an ACC Nightstalker Level 2 torque converter, only because the cam needed the higher stall. I'm staying with the 3.27 gears for now, because of the 80 mph speed limit on our highways and I plan to add nitrous in the future. I haven't rung the motor out yet, because I've only got maybe 100 miles on it so far, but it seems like the 3.27 gears won't be an issue. As mentioned above, a stock motor really doesn't need a higher stall converter. I think you'll find the Bauman shift kit and 4.10's will give you all the benefit the stock motor can provide. Definitely install a plate type trans cooler! You want to keep the fluid cool. Have you done the typical bolt-on upgrades?

Thanks for your response.

By typical bolt-on upgrades, so far I have installed: sn95 5 lug conversion with cobra brakes, 17 inch wheels, cold air intake with new throttle body, exhaust headers and tailpipes.

I am still confused about the transmission cooler, as I have also been told that I don't need one since I am running a stock converter, with the only mods being the shift kit and the 4.10 gears. Do I absolutely need it? I drive between 20-50 mph, with 60-70 mph being rare in the UK unless I plan to travel across the country.

If I absolutely need a plate type trans cooler, can you recommend me any kits which would work with my car? If not, what parts do I need for a 91 convertible fox?

Thank you.

Mustang5L5 · Jun 10, 2022

Heat is the worst enemy to an AOD. The stock cooler is part of the radiator and uses the coolant to cool the trans fluid, but I would recommend going with a decent air-to-air cooler in front of the condenser instead.

Middleagecrisis · Jun 10, 2022

You absolutely need an auxiliary cooler, there are no downsides, only benefits to keeping the fluid cooler. Use in conjunction with the factory radiator cooler, but route the cooler lines to the auxiliary cooler before you go into the factory radiator cooler. You want to cool the fluid before it goes into the radiator cooler. I also have a 1 qt. deeper finned aluminum pan that I bought from Summit for ~$100, not necessary, but another benefit. I used a Hayden (HDA-678) plate cooler that I bought from Summit for $48.99. Sounds like you've got the bolt-on situation handled. A bigger Mass Air unit might be another option, if you haven't already done that, but only so much you can do with the stock intake, it's very restrictive. Hope this helps

91 GT Convertible AOD Upgrades

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