Went with Dexron-VI. I don't understand why it's not a more popular choice. It's synthetic, but it's also actually approved for the trans by GM, unlike other synthetics.

The old fluid @ 19,800 miles looked good. No shavings or metal flakes or anything. Still somewhat reddish.

Next up is the diff, which hopefully will also be metal flake free!

I want to say the car shifts smoother. It felt like it. But I can't rule out it being completely in my head. It wasn't too bad before, except of course reverse and the occasional difficulty with first.

 

I am going to be doing the same with my car. I just picked it up and gonig to work front to back. Engine oil, trans oil, diff oil. Probably in that order too.

Its good to hear yours went well.

 

Yes, I got mine last July. I did the coolant and engine oil first, guess I took a while to get around to the trans, though I bought it with 13k miles on the car, so it didn't seem too pressing.

 

I wonder why GM doesn't recommend Dexron VI in manual transmissions calling for Dexron III?

#04-07-30-037E: Release of DEXRON-VI Automatic Transmission Fluid (ATF) - (Apr 7, 2011)

Attention: DEXRON®-VI Automatic Transmission Fluid (ATF) is the only approved fluid for warranty repairs for General Motors transmissions/transaxles requiring DEXRON®-III and/or prior DEXRON® transmission fluids.

---snipped----
MANUAL TRANSMISSIONS / TRANSFER CASES and POWER STEERING
The content of this bulletin does not apply to manual transmissions or transfer cases. Any vehicle that previously required DEXRON®-III for a manual transmission or transfer case should now use P/N 88861800. This fluid is labeled Manual Transmission and Transfer Case Fluid. Some manual transmissions and transfer cases require a different fluid. Appropriate references should be checked when servicing any of these components.

Power Steering Systems should now use P/N 9985010 labeled Power Steering Fluid.

Consult the Parts Catalog, Owner's Manual, or Service Information (SI) for fluid recommendations.
---snipped----

 

Is Dexron VI synthetic ?

 

That bulletin is interesting.

And yes, Dexron-VI is synthetic.

 

I don't see the words "synthetic" on any of the "ACDelco" or "GM Vehicle Care" Dexron VI containers but there are synthetic blend and full synthetic versions available through the aftermarket.

 

Ahh, fair enough. I thought I had read that. Perhaps whatever I read said that at the time only synthetic could meet the spec. Dex 6 is supposed to have twice the service life of Dex 3, which is why they called it that. And apparently that required a synthetic to accomplish. Or it seemed it would at the time.

I imagine any base stock or blend that can meet whatever the Dex 6 spec is would work.

Looks like the Castrol I put in there is a blend. Thanks for pointing that out!

 

I believe this was already covered in the trans section, and the conclusion was that the newer fluid had additives that were harmful to the syncho material.

 

Yeah I definitely don't agree that Dex VI is a good replacement for all applications previously requiring Dex III. That goes for automatics and manuals. For instance, I put a Castrol Syntec Dex VI in my Fleetwood (4L60-E) and it shifted like crap. Yet the same fluid in my wife's 2000 Malibu (4T40-E) shifts perfectly. I'd stick to a Dex-III fluid in the T56. I'm using Amsoil torque drive in mine.

 

is there a diy faq thread on how this is done

 

I have read the same. Some guys that have used the Dexron VI, started to have shift problems.

Part #88861800 is what Dexron III is now called by GM.
I have also read that GM let the Dexron license expire in 2006.

I used the Castrol ATF (not synthetic) in the Trans, that is compatible with Dexron III spec.

I used Valvoline (Limited Slip) synthetic 70/90 in the Differential.

 

Allison Transmission is also addressing Dexron VI 'upgrade' issues/problems.

 

Yep DEXRON III is all you should be using. The DEXRON IV is harmful to some components in the manual tranny. I researched the **** out of it before i filled the t56 in my mustang. I would swap the IV back out for RP Syncromesh or regular DEXRON III

 

What about just running mobil 1 full synthetic atf?

 

synthetic is not good for the tranny.

I have read many posts by vendors on here in the manual trans section saying OEM Dexron III or any of the ordinary dexron III non synthetic is what you want to run.

 

Link? Also, was this for all T56's? I don't think I'd put it in a '90s or early 2000's one. But that powertrain document for the '06 trans seems pretty clear.

 

If the transmission spec calls for "Dexron III" then you'll be totally fine. I have been running Mobil 1 Synthetic ATF for the last 2 years with absolutely postively no issues. There are many members here for years running Mobil 1 ATF in their T56s. Don't confuse "synthetic" with "Dexron VI (6)."

From Mobil's website on Mobil 1 Synthetic ATF:
"Mobil 1 Synthetic ATF is recommended by ExxonMobil for use in applications requiring: GM Dexron IIIH, GM Dexron IIIG, GM Dexron IIE, GM Dexron IID, GM Dexron II, GM Dexron"

 

There are lots and lots of people running synthetic fluid in T56s, including in road race applications, without issues. I've seen 240F tranny fluid temps on track, so I have run and will continue to run synthetic in mine.

 

yeah i thought the later revision t56 units have no issues with synthetic. I'm running amsoil synthetic in mine... no probs. Actually made it shift better I think. The oem fluid looked TERRIBLE at 30k miles. Glad I changed it.