What can I use in a trans that has had Dexron ll ?

Dex II is an old GM spec replaced by Dex III which has been around forever. Might see it labeled Dex/Merc. Not to be confused with Dex VI.

I've been using John Deere Hy-gard for many years in my 727. A super stock racer told me to try it and it's cheaper (over here in the uk at least) than DXII. Didn't make the car go any quicker or slower and we've had no issues with the stuff, even when the 'box was behind a 4 figure 655ci engine.

The latest Dexron states it is "Backward compatible" meaning it can be used in older equipment that specifies a previous Dexron formulation. This is what's stated for a jug of "ACDelco GM Original Equipment 10-9395 Dexron VI Automatic Transmission Fluid - 1 gal."

STP Dexron / Merc Automatic Transmission Fluid

Dextron/Mercon from your local parts store

Dex VI has friction modifiers and is more "slippery" than Dex III. It is also synthetic where Dex III is not. And Dex VI is typically more expensive.

Compatible, but not the same. In a performance application, Dex III would likely be more desirable, since converter shudder is not a consideration.

Which nobody asked about

Sorry. I didn't know taxi cabs and Granny's old 318 New Yorker were popular topics on this site. A little context would help.

You could probably put peanut oil in a 727 and get by with it. No need to sweat the decision.

Doesn't matter if someone did or didn't , DexIV sounds like ATF 3/4 , friction modifiers added to help a lockup convertor SLIP upon application . If the OPs trans does not have a lockup converter the last he , or anyone else without a lockup converter wants , is more slippage in clutch packs that don't need to slip on application.

speaking of lockup converters..........
my wife's car had a shudder when the converter locked up, and it kept getting worse.
i changed oil and filter, but no change. the oil was bright red, no smell, and just a tiny trace of gunk in the pan.
i discovered [quite by accident] that adding a small tube/bottle of mopar brand additive for limited slip rears cured the problem, and has worked for many thousands of miles since. to say i was amazed was an understatement !
just what my personal experience was, and your mileage will surely vary.............

Since the subject is compatibility i.e. "being able to exist together with no ill effects", just about any current transmission fluids can be mixed. While other fluids could be used and would work, they're not necessarily "compatible".

ATF 3/4 has varying amounts of Lubegard added to address exactly what you had happening , but to me there is a line where too much of that stuff may cause issues inside the trans itself . Where it's just your wife's DD it's probably not an issue adding more , but in a performance application I wouldn't trust it . I stopped using the +3/+4 in my 2000 ram with a Cummins at the first fluid change , 30k , didn't have any issues and the shudder I did experience was because of the wonky programming by Chrysler of getting the trans into OD and Lockup at 40MPH which with factory tire size and 3.54 gears gets you lugging the engine at 1300 rpm , drop it out of OD and the problem goes away . I have a stock 98 2500 rwd and I have the same problem , I really don't want to switch to 4.10's which would move the RPM up high enough that it would go away .

Adding sure grip additive reduces clutch capacity.

Guys on the Chrysler Tech Line recommended it back in the day and it did work to alleviate L/U shudder.
But on 40/41TE, 42LE and 42RLE it could cause L/R clutch failure under severe conditions.

For daily passenger use it worked in most apps.

The additive also attacks bronze bushings.

"The additive also attacks bronze bushings."



interesting. could you please explain ? [TIA !]

As I suspected , that's an interesting note on the limited slip additive attacking the bronze which isn't an issue on a rear diff because there isn't an bronze parts in one.

I don’t remember the exact reaction to the yellow metals, or how long it took. That was over 30 years ago.☹️