hey guys

Looking to replace the tranny fluid in my 89 formula t5 since i don't think it's ever been done before. From what i've researched it should take automatic tranny fluid (it's a world class T5) and it should be dexron III.

The problem is i can only find DEXRON 6 which claims to be backwards compatible with III and II. was looking at AC Delco Dexron 6 since i think that's what's closest to original, here's the link

you guys have any thoughts or suggestions on what's best to use? is Dexron 6 truly backwards compatible?



thanks in advance

The internet isn't backwards compatible with Dexron III.
But getting off your keister and buying Dexron III in person fixes a lot of Google Fu white belt problems.

Dexron VI will be fine for it.

None of the local parts stores around me carry it but thanks for your insightful comment.

Yes they do, or else you'd have a location in your profile.

Dex 3 hasn't been available (at least not widely) for 25 years or so.

The reason the transmission "specifies" that is because at the time, that was the current version. Incredibly enough, those engineers, however smart they may have been (although giving that transmission model the nickname "World Class" makes me think they were all a bunch of bozos living under a rock they hadn't crawled out from under since ... a long time, and they made their summer co-op do ALL the work instead of just the 90% of it that's boring and technical like most companies) weren't aware of how the ATF specs would be updated in the future.

AFAIK the only way to get it nowadays, is to pay extra for special packaging that they print "Dex 3" on the same ATF they print "Dex 7" on (or whatever version of it they're up to now) because you're one of those people that doesn't understand that it's ALL backwards compatible. Just like, you won't ruin a motor from the 60s if you put SG motor oil into it instead of SC.

Whatever ATF you buy at the store today, any normal garden variety of locally produced no-name on up to top brand-name synthetic, will work fine. Which revision of the Dexron spec doesn't matter, as long as it's 3 or greater.

also most places still sell DexIII. Just look for the bottle that has DEX/MERC on it.

Nope... that's Dex 6. (or 7; whatever it is this week)

Doesn't make a damn bit of difference though. Just go buy some ATF and get it over with already. You don't have to find it with the "vintage" spec still printed on the label. ANY ATF you buy today is perfectly acceptable. ANYwith a capital "N". Capische?

running SM or SN rated oil in an engine with a flat tappet cam could very well cause the lobes to go flat. it's documented, there were a whole lot of cams that went flat right around the time they made the switch from SL to SM oils.. so not everything is always "backwards compatible".

i don't know anything about what they did to Dexron for the 6th version, but it's very possible that they took something out of it that older manual transmissions need to survive. i know some people have reported problems with older automatic transmissions with the new fluid.. research is always a good idea.

I'm a service writer at a GM dealership and DEX 6 is ONLY backwards
compatible with AUTOMATIC transmissions. Not manuals...I got into a discussion about this with 2 techs of mine when me and one where working on my 91 Firebird with a V8 and WC-T5.


Reasons why not to run Dex 6 in our WC-T5s is simple, Dex 6 is a synthetic and its more lubricity and can do harm to some carbon friction parts I believe in a WC-T5 and burn them up over time. Just like they say don't run gear oil in WC-t5s but you can run DEX 3 in NON WC-T5s because of some of the brass parts.


So I just went got a thing of Valvoline DEX/Merc and perfectly fine. Though I did find out their is some oil that GM makes to run in T5s but i'm still investigating that.

The shop that rebuilt my WC T5 this past fall recommended Mobil-1 Synthetic Multi-vehicle ATF.


Since he insisted on it for warranty purposes, and it's his dime if it blows up, I'd assume it's a safe bet.


I've put 4,000 miles on my T5 since reinstalling it, and using his recommended fluid, and have had no issues.

AMAZING how that one simple word, all by itself, generates myths out of thin air!!!

A whole shipload of smart inventive imaginative educated people deliberately bending their minds toward it couldn't come up with crap like this; but ONE numbnutz can do it single-handedly.

I guess it's really true: it takes an idiot to make a village.

I've reread your post several times...I'm not trying to be difficult, or flame here, just trying to understand what you were trying to say.

To clarify, I don't claim any special knowledge or understanding of the pros or cons of synthetic versus mineral derived ATF...


The shop that rebuilt my T5 specializes ONLY in manual transmissions, specifically T5's, and the T56. All I did was relay what the rebuilder recommended. Since he actually has to fix them under warranty if things go south, I have serious doubts he's likely to recommend something that would create a problem.

Who me???

If you're asking me, I was referring to the post above yours, not yours.

"Synthetic" seems to bring out that sort of thing. It's almost like we can pick out any sophisticated-sounding long or obscure word out of the dictionary, or even an unusual form of a common word, and pair it with "synthetic"; and the people who didn't pay much attention to anything in school, will fall for it.

Let's play a word game:

"Synthetic [fill in the blank your favorite fluid] is bad because":

Here's a few words to start with. Mulct, conflagration, demurrage, eructation, ... go ahead and add a few of your own. Throw darts at a dictionary page or something.

You could even make a drinking game out of it: surf car-related sites on the Internet, and for every post you come across about why "synthetic" something or other is bad, chug a beer. Wow, my Friday night is looking better already...

That made perfect sense....thanks!

And, just as a FYI:

For the last coupla T-5s I ran, which were the 2nd design, I put Mobil1 in them; and they worked perfectly fine for quite a few years.

You know...I have to agree with sofaking. At what point do you just get it done and over with? You know what's interesting? BORGWARNER makes these transmissions for our cars and ALSO other vehicles. For instance, the same (for all intensive purposes) T-56 in a 90s viper and 90s camaro are nearly the same. Granted input shafts, gear ratios possibly, maybe different style bearings. Between those TWO transmissions built by BorgWarner, what do you think the MFG of either the Dodge Viper or Chevy Camaro recommend filling the trans with? That's right. Vipers suggest ATF+4 while the Camaro suggest Dexron.

Now looking at that, WHAT do you think is the bigger picture of things here? What can you take away from this? Simple. Those transmissions are made to be ran with ATF. Why? Because of the composite synchros vs the non WC that used brass synchros. Also because the WC uses more needle bearings that sleeves as the non WC. Little things.


What would be INTERESTING is looking at an oil analysis between Dex III, Dex VI, ATF+4, etc. and COMPARING what's actually in it. I tried searching on bob'stheoilguy for these, but mostly you'll probably find the viscosity is a tiny bit difference, and a few additive amounts.

What I always ran in the T5s after rebuilds. Stangs and f-cars.

You're right.

What's interesting is GM did release a memo re: the approved use of Dex VI some time back and later rescinded it for the manual Tremec vehicles.

ATF+4 wasn't out in 1992. Early Vipers did have Dexron II tags on them from Borg Warner.

Shore...but from 92-02. ATF+3 or ATF+4. Same idea that was mentioned above with Dexron. Even with the Stang Cobras and their trans.

Synchromesh is made for brass synchos to my understanding. The nonWC that works great in and also the NV2500 or NV3500 transmissions.

You use ATF for composite style synchros.

From what I'm reading online about synchromesh, it seems some people use it in their composite synchro trans as well.


http://www.bobistheoilguy.com/forums...Number=1114224

To me, the trans feels better with synchromesh and have always used it with the fiber blocker ring clutches.
Got turned on to it by D&D, they recommended it.

I have been using ATF with a pint of MT-1 (military grade yellow safe) gear oil.
The gear oil adds sulfur (lubricity) and helps with 25 plus year old transmissions ware issues.

As always.... your mileage will very.
some have good results with water and gravel and some have good results with OE only and some have good results with there own snake oil mix.