Wow your AOD is being really nice to you. At least it's warning you of a potential problem; mine didn't! How does your fluid look and smell? Brown & burned? Red & sweet?
A grinding sound before each shift, eh? Ooh boy, I guarantee if you take it to any transmission shop they'll want to install a totally new/rebuilt unit. Is it really before
every single (UP OR DOWN???) shift the trans makes, or is it just one or two gears? I'd suggest you stop driving it until you can drop at least the valve body and see the contents of the pan. While you're doing that, change the fluid and filter. You'll probably also want to take apart & spray out the valve body with brake parts cleaner. If you've never done this it's a good idea to find someone to help who has, plus it'll help it shift quicker & cleaner, if it can be simple as this. As to what the problem actually is, without being there to hear it I could only make a stab in the dark. I hope it's not your direct drum and shaft stripping their splines out. Maybe you'll be "lucky" and find the torque converter's internal splines eaten away like I did.
To see if your TV cable is set correctly,
click here. Find the AOD links and you'll see a half page devoted to setting this very important piece of the AOD puzzle.
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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch