My first car with FMX

This is my first time owning an FMX car. I have had a 302 with C4 and 351W with toploader in my previous 2 Mustangs. I have a couple of questions, but will address one issue at a time. 

When I pull the car out of the garage and into the driveway I've experienced the following symptom. The driveway has a small slope to it. So if I put the car in neutral, it will go backwards. So when I have it in reverse and pull out, I shift into Drive while the car still has momentum and is going backwards, and it behaves as if it were in Neutral even if I give it a little gas (so it keeps rolling back). If on the other hand, I back out, come to a complete stop, and then shift into Drive, then I can feel the transmission engage and it moves forward as expected. I have not tried to replicate this since the last time this happened which was about a month ago.

I have also noticed, twice, that in the same right turn to come out of my subdivision, while turning, its like the tranny goes into Neutral (while in Drive), and then engages again a couple seconds later.This happened probably about a month ago as well. I have driven it 2 or 3 times after that, and have not had any issues in that right turn.

The rest of the time, it has not shown any other signs of slippage or issues while driving. I have checked the fluid level (with the engine running), and it is fine. Does this mean the tranny is starting to slip and might be due for a rebuild?

How long had the car sat before you drove it and first experienced the problems? Sitting for long periods can cause two problems, the internal soft parts (seals, etc.) can dry out and loose flexibility, causing various components to not function correctly. Sometimes they can recover after being driven, sometimes not. I'm not a big fan of transmission reconditioning additives, but a good name brand like Lucas would be worth a try if the problem persists. The other possibility is the torque converter can drain down and until it's refilled can cause low pressure to some components, in addition to not being able to transfer torque.

Because you live in Texas I doubt if you are experiencing cold weather problems, which can cause slow reactions until the fluid and parts warm up some.

Did you check the fluid level after you had driven it for a while, to make sure all air has been purged?

The FMX is very sensitive to correct fluid level and correct trans fluid (Type F).

Might want to drop the pan, change the filter and fluid and see what the fluid looks like.

The FMX is very sensitive to correct fluid level and correct trans fluid (Type F).

Might want to drop the pan, change the filter and fluid and see what the fluid looks like.

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+1 I had a tiny weep at the vac modulator on my FMX when I was running it and if the fluid was at all low it would start to act up similar to what you describe.

Thanks for the suggestions. I had no idea this transmission required this much attention to detail. I usually take the car out for a drive on the weekends, so it most likely had been sitting for about 1 week. The car was at normal operating temperature when I checked the fluid level as I had just come back from driving it for a while. I will probably look into dropping the pan, changing the filter and adding Type F fluid. Hopefully that will take care of the issue. The 2 times I have had the issue in the driveway, it has been right after starting it while it is warming up.

Since I was preparing for the worst. I found a guy selling an AOD from a 92 Mustang with 20k miles, including the crossmember, TV cable, what I am guessing is a kickdown cable (I am not too familiarized with AODs), shifter, flywheel, torque converter, cooling lines, radiator, fan, driveshaft, and could not pass it up. So I have all of that in my garage. If the issue with the FMX is fixed by changing the filter and whatever fluid is not in the TC; I would probably not got through with the swap.

Thanks for the suggestions. I had no idea this transmission required this much attention to detail. I usually take the car out for a drive on the weekends, so it most likely had been sitting for about 1 week. The car was at normal operating temperature when I checked the fluid level as I had just come back from driving it for a while. I will probably look into dropping the pan, changing the filter and adding Type F fluid. Hopefully that will take care of the issue. The 2 times I have had the issue in the driveway, it has been right after starting it while it is warming up.

Since I was preparing for the worst. I found a guy selling an AOD from a 92 Mustang with 20k miles, including the crossmember, TV cable, what I am guessing is a kickdown cable (I am not too familiarized with AODs), shifter, flywheel, torque converter, cooling lines, radiator, fan, driveshaft, and could not pass it up. So I have all of that in my garage. If the issue with the FMX is fixed by changing the filter and whatever fluid is not in the TC; I would probably not got through with the swap.

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It is a little finicky especially when cold. That being said I think you would be very happy with the AOD swap.