Transmission Fluid change

Jae 'Bird

Jae 'Bird

4th Gear Poster
Joined
Dec 11, 2023
Messages
244
Age
20
Location
Edmonton, Canada
Vehicle Details
1990 Ford Thunderbird Base with PEP 151A, 3.8L NA V-6
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So I am going to be pulling the car out of storage very soon and the first thing I want to do is change the tranny fluid. I want this to be a thread for others to reference in the future regarding the AOD fluid change and also a double check thread where I make sure I have everything in order to make this go smoothly (and a place to ask questions if something unexpected happens). I will list the tools and parts I have and then you can add things in that I either might want or absolutely need for this process. If I don't mention it, please ask if I have it (parts or tools) even if it seems obvious, I will not take it as an insult, I liked getting double checked. I will also have some questions farther down

So far I've got
- a safe way to lift and support the car
- wrenches and everything I think I'll need to remove the bolts and whatnot
- Breaker bar to turn the engine to get the torque converter bolt accessible
- 12 Qts of Mercon transmission fluid (Canadian Tire still has mercon and it was on sale)
- 1 Qt of Lucas transmission fix
- Wix transmission fluid filter and new pan gasket
- pan cleaning things (brake clean, rags, plastic razor for the sealing surfaces)
- drain pan and a way to measure how much fluid comes out
- Thread locker if I need it but I don't think its needed for any bolts
- torque wrench to properly torque the bolts
- Haynes manual to reference and for the torque specs

The reason for the lucas is I used it several years ago because shifting it was a little sharp and it helped quite a bit, I also like it for a preventative measure going back together to keep the clutches good. I assume this is original fluid coming out as my Dad (the previous and only other owner, doesn't recall the fluid every being changed). However, I have always kept a close eye on it and it is always at the right level and is still a decent pink color so I think I am safe to change it, the car has 181,000 km (112,468 miles)
Now for some quick questions,
I want to confirm that draining the torque converter is fairly easy, I think i just turn the engine until the plug shows and then undo it right? I don't need to remove extra parts to get to it right?
is there any checks or things I should look for while I'm looking at the bottom of the valve body with the pan off?
Are there any torque specs that aren't in the manual that I need to know?
I appreciate any and all input, this will be my first time doing this maintenance.
 
If you have help, you may be able to just crank the engine over with the starter. Just pull the coil wire so it won't start. Otherwise looks pretty good.
 
Commonly there are 2 different filters count the bolts on your pan to ensure you get the right one
 
IIRC since its a 90 it has the older model transmission, Mercon is fine to use. But Mercon V is backwards compatible, and usually considered better fluid.
I did the same fluid change and drained the converter back when I was a teenager on my crown vic. If my dumbass teenage self could do it, can't be too hard. Just take your time and make sure car is supported well. It can be messy though so make sure you have the oil absorber ready!
 
3_97_Sports said:
Make sure it is mercon v and not just mercon.
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I see what you mean, although like Kenz said, its the AOD so I believe I am fine to use Mecon, I could have gotten Mercon v but Mecon was on sale and I figure either way new fluid is gonna be better, I just checked the manual and it does say Mercon, I know either would be fine. Thank you for the check
 
If the fluid has never been changed, when you drop the pan there will be a little plastic plug with an O-Ring in there. It is used to plug the dipstick hole until the transmission is assembled to the car. They just pushed the dipstick into the hole and pushed that plug into the pan. It doesn't hurt anything being in there. Rare to see them anymore since these transmissions are so old nowadays. If you are feeling saucy, you can replace the pan with a new pan with a drain plug on it. Makes future fluid changes much easier/neater.
 
In my experience, turning the engine doesn't require a breaker bar. It's easy to turn with a ratchet.

Make sure you have a large drain pan. The torque converter alone yields 7 quarts.

Removing the pan is much easier if you siphon out the fluid through the dipstick tube first (4 quarts).

The remaining 2 or so quarts are in the various lines, valves, and the cooler. You can flush the cooler by disconnecting the exit tube and replacing it with some translucent plastic tube from the hardware store, going into a receptacle. Start the engine and monitor fluid coming out while a helper pours fresh fluid into the dipstick tube. This process can waste fresh fluid though.
 
Jim3inVirginia said:
Everytime I change the transmission fluid in mine I wish I had replaced the stock pan with one with a drain plug.
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I've read that many times, but I just don't see the point when you can easily siphon the fluid in the pan through the dipstick tube.

Hand pump $5; new pan with drain plug $50 (guesstimate). I know which I prefer.

@Jae 'Bird , I also recommend reusing your pan gasket. It's probably better than any aftermarket gasket.
 
1997ThunderbirdLXV6 said:
I've read that many times, but I just don't see the point when you can easily siphon the fluid in the pan through the dipstick tube.

Hand pump $5; new pan with drain plug $50 (guesstimate). I know which I prefer.

@Jae 'Bird , I also recommend reusing your pan gasket. It's probably better than any aftermarket gasket.
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You siphon it out and then remove the pan to change the filter?
 
Grog6 said:
dorman pan with plug 26 bux on amazon, up from 20 last year.
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That's a great idea, except dorman doesn't make one for the AOD, unfortunately. I checked Amazon and the Dorman website and it is nowhere to be found.
 
1997ThunderbirdLXV6 said:
I've read that many times, but I just don't see the point when you can easily siphon the fluid in the pan through the dipstick tube.

Hand pump $5; new pan with drain plug $50 (guesstimate). I know which I prefer.

@Jae 'Bird , I also recommend reusing your pan gasket. It's probably better than any aftermarket gasket.
Click to expand...
what type of gasket would be there now? The Wix filter I got comes with a decent looking rubber gasket, I guess I will carefully inspect the one that comes off, and if I feel confident in it then I will reuse it.
 
Sorry, missed the aod part. Advanced sells a drain plug you can put in your pan, but you have to use rtv or it drips.
 
1997ThunderbirdLXV6 said:
I've read that many times, but I just don't see the point when you can easily siphon the fluid in the pan through the dipstick tube.

Hand pump $5; new pan with drain plug $50 (guesstimate). I know which I prefer.
Click to expand...
Pumping it out through the dipstick tube works just fine too, but personally, I'd much rather remove a drain plug on the pan than spend 20 minutes pumping fluid out. I've done both to prevent making a mess. I had to service a late model Subaru transmission last weekend. It was so nice having a drain plug on the trans pan.
 
Ok urgent questions so I can convince my parents that I really can do this fluid change in one day.
Are there any bolts that are easily broken or stripped?
I know to be carful in general but there's none are especially breakable right?

Can someone give me clear steps on how to drain the torque converter?
My memory of the undercar is fuzzy cause its been so long but where is the access to the torque converter bolt? Do I need to undo the pan first or something else to access it after I spin the engine?

Also, before I lift the car, what gear should I put it in? I might be thinking wrong but wont neutral mean that spinning the engine doesn't spin the torque converter?

Thanks for your guy's help, I seriously can't thank you enough
 
Jae 'Bird said:
Ok urgent questions so I can convince my parents that I really can do this fluid change in one day.
Are there any bolts that are easily broken or stripped?
I know to be carful in general but there's none are especially breakable right?
Click to expand...

I don't think you'll need a whole day!

Do you have the torque values for all bolts involved? I remember they're not particularly tight at all; I don't think there's a high risk of breaking anything.

Jae 'Bird said:
Can someone give me clear steps on how to drain the torque converter?
My memory of the undercar is fuzzy cause its been so long but where is the access to the torque converter bolt? Do I need to undo the pan first or something else to access it after I spin the engine?
Click to expand...

It's ideally a two-men job: one person under the car; remove a small rubber plug in the bellhousing; observe the torque converter inside. The other person very slowly spinning the engine clockwise seen from the front (or whatever the engine's normal rotation is). Under the car, you look for the plug and immediately tell the other person to stop when you see it. Then you just unscrew the plug and drain it. I did that before the pan.
The Ford manual calls for a new plug, but I reused mine, as does everyone else apparently.

Jae 'Bird said:
Also, before I lift the car, what gear should I put it in? I might be thinking wrong but wont neutral mean that spinning the engine doesn't spin the torque converter?
Click to expand...

No, the torque converter is bolted to the engine; it spins regardless of gear.

I cannot remember putting it in anything other than Park...but now you have me wondering. In any case, it would be either Park or Neutral.

Once you get to the refill stage, you'll have to start the engine at some point to fill the torque converter.
Say the whole system takes about 11-14 quarts, not sure how much exactly, about 7 quarts go into the torque converter; but you can't just pour them in. The fluid has to be pumped into it.
So you fill the pan, about 4 quarts. Then one person starts the engine while the other person keeps pouring in fluid. This part you can also do on your own.
 
Thank you so much, this was very helpful, one last double check, since your car is the late model withe the 4r70w, do you still think everything applies to the AOD? I know its probably similar, but just want to double check
 
Jae 'Bird said:
Thank you so much, this was very helpful, one last double check, since your car is the late model withe the 4r70w, do you still think everything applies to the AOD? I know its probably similar, but just want to double check
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You'll have to wait for the real experts to chime in there.

I  think it applies...but I never researched AOD to 4R70W differences.

I did two fluid changes myself: one where I flushed through the cooler line (without taking off anything under the car), and one where I drained the torque converter and the pan and changed the filter.

I'm happy to share my observations with you, but there are guys on here who have done this service literally a hundred times! Though they might be sleeping right this moment.
 
Ohh, and not sure if anyone mentioned this: if you spill even the tiniest amount of transmission fluid onto your exhaust, it'll cause a huge, dense white cloud of smoke as the fluid evaporates. It's apparently harmless, but it can be scary if you don't know what's going on.
 
Jae 'Bird said:
Ok urgent questions so I can convince my parents that I really can do this fluid change in one day.
Are there any bolts that are easily broken or stripped?
I know to be carful in general but there's none are especially breakable right?

Can someone give me clear steps on how to drain the torque converter?
My memory of the undercar is fuzzy cause its been so long but where is the access to the torque converter bolt? Do I need to undo the pan first or something else to access it after I spin the engine?

Also, before I lift the car, what gear should I put it in? I might be thinking wrong but wont neutral mean that spinning the engine doesn't spin the torque converter?

Thanks for your guy's help, I seriously can't thank you enough
Click to expand...
Engage the parking brake! I always put it in park, that way the rear wheels won't move easily. But it can be in any gear with the engine off, turning it by hand wont develop pressure to engage a clutch. None of the bolts should be tight enough to break.
You can do it by yourself, as long as you can look in the hole ( there's a round rubber plug in front of the pan,small screwdriver to remove it) while turning the 18mm socket on the crank. tc bolt is npt tapered, finger tight it, then 1/4 turn. 6 quarts will refill it, if you don't remove the valvebody. seems to be 4 quarts in the tc, 2 in the pan, 4 more if you drop the vb for a jmod. It should be doable on ramps,in a couple of hours, without the jmod. I do the oil at the same time.
pan bolts are 8mm, do not overtighten. You will deform the gasket area of the pan. Torque to 12-15 ft-pounds.
I have 4r70w trans', but the aod is close. Big difference is tv cable vs electronic control. There's a grommit on the tv cable that wears out, but I've never seen it.

Wear safety glasses, getting mercon in your eye hurts like hell. While you have the pan off, take a pic of the magnet, then use a rag to pull it loose, clean it off, and put it back, after wiping the pan clean inside. I usually clean the outside and paint it, but that's just me.
Refilling, I put 4 quarts in the pan, start the engine, and with your foot on the brake, shift it thru the gears, letting each one engage before moving on to the next. ending back in park.Get out and check the fluid level add 1/2 qt at a time until it gets to full cold.
Take it for a drive to the store. When you get back, check the fluid again. If it's between full cold and full hot, you're done.
I park over an open newspaper after, just to look for drips.
1/2 qt low is better than 1/2 qt high.
Pan magnet crud: This shows state of the trans. Post pix. Metal chunks=bad, black crap is wear, normal unless excessive. Post magnet pix; I have some terrible ones,lol.
 
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