I need to ad about a quart of auto trans fluid after losing some due to a radiator and trans line change. Car has BB 727.

I'm not sure what the PO used, but almost positive it's not synthetic. I'd bet it's either Dex/Merc, or less likely ATF+4. He doesn't remember.

So, assuming that it's either of the two, what would it be safe to top it off with? I can't seem to get a straight answer from the side of any bottle or from the internet on what the compatibility of either type of fluid is. All conflicting answers...

Really don't want to drop the pan unless I have to for a full fluid change. What are my options for topping off?

If you can't get an answer from the PO, I'd be inclined to bet it's Dex/Merc for a normal street-driven older car.

No way to tell really.

If it is a restoration or daily driver I would guess Dex/merc.

If it is a street/strip or otherwise modified I would guess Type F.

I'd use Type F. No problems mixing trans fluids anyway.

Use whatever's handy.

Ummmmm....my step father (40+ yr mechanic) would disagree. He always told me "don't mix trans fluid or you might get foaming...pick one & stick with it" He most certainly meant "don't mix Dextron II with Type F" based on his age. I've never tested it, but I've always followed his advice.

Nonsense, all modern ATF's have anti-foaming additives.

BTW, my favorite fluid is a 50/50 blend of type F and Dexron.

So I had some Dex/Merc handy so I added it a pint at a time while idling in neutral. I added a total of 1 quart to get the level to the full line on the dipstick. After taking the car for a spin, the level was about a quarter inch above full. Guess it wasn't hot enough when I was adding fluid.

Is a little overfill going to hurt? Should I remove some?

A little under is better than a little over.

This one is always a controversy.

I vote Dex/Merc because trans expert who's had a shop in my area for decades advised me to use Dex/Merc.

I have to change the speedometer gear, so I can remove some fluid then. Thanks!