'99 FRC with MN6 transmission. Been searching for days and haven't come to a definitive conclusion on which type/brand of ATF to use.
Some say stay away from synthetic because I might have paper blocking rings. Others say it doesn't matter, go for a synthetic.

I settled on the factory ACDelco stuff. When I searched, I couldn't find anything that said DEXRON-III on the bottle.

Is this the correct fluid?

I

 

pm C66 Racing on here, he is Amsoil dealer and will make recommendations, stand behind his product, and give you a good price. I've done it for 3cars (iirc) and highly recommend.

 

AMSOIL makes an excellent ATF that can be used in the early and or late model MN6 transmissions. Yes it does matter for the early MN6 in that you should not use anything but the DEXIII or equivalent.

If it were me, I would use the AMSOIL Torque Drive. Its synthetic, compatible with your early MN6 and a very stable fluid.

BC

 

I see the Amsoil crew has already jumped in with their opinion. To answer your question, no, that's not the exact fluid that GM recommends for the T56 nowadays, although it would probably work. The correct part number is 88861800, or AC Delco 10-4033.

I've used a couple different non-synthetic ATFs in mine and never noticed any difference. Castrol, Valvoline, SuperTech, they all worked fine for me. I don't think there's any need to go out and spend a lot of time or money getting something special, but if you want to be 100% sure it's right, then AC Delco is a good choice. Good luck.

 

Thanks TastyBacon.

I just talked with my local GM parts/service department and asked what I should use and their first answer was the ACDelco part number you referenced above (manual trans fluid). Then I told them the side of the transmission says to use Dexron III only. So he consulted with another individual in the shop that told him Dexron VI is the correct fluid to use. Now I'm more confused. I'd prefer to use a non-synthetic fluid in this particular application.

 

There are multiple bulletins out from GM instructing dealers NOT to use Dex VI in any manual transmission that specified Dex III, as it can cause failure. If your dealer told you to use it, find another dealer. Here's an extract from one of the bulletins - #04-07-30-037E: Release of DEXRON-VI Automatic Transmission Fluid (ATF) - (Apr 7, 2011):

"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."

When they introduced Dex VI, GM started selling their own "Dex III" now called Manual Transmission Fluid - see above. But beware, GM has produced multiple "Manual Transmission Fluids" over the years all for different applications and with different part numbers. Therefore, make sure the part number is correct if you want to go the AC Delco route.

You absolutely need something that meets the Dex III spec. I am running Valvoline Dex/Merc, which meets the spec (says so on the container) and is easily obtainable - gallon jug from Walmart and others. You also have a '98 (as I do), which means the trans does not play well with most synthetics - parts were changed internally on later 'boxes, so they can safely use synthetics.

 

Thank you for this detailed response!

Two questions:
1. The first line of the service bulletin states, "The content of this bulletin does NOT apply to manual transmissions or transfer cases." This directly conflicts with the next sentence. What am I missing?
2. I saw other brands of ATF that reads "Dex/Merc" on the label, but wasn't sure if it meant Dexron III or VI. Does "Dex/Merc" translate to Dexron III compatible in most or all brands?

The GM dealer's (which I have no particular loyalty to) first answer was P/N 88861800 as you stated. As I told him the transmission case itself had a sticker that said use Dexron III only on it, he decided to consult with someone else. Then he came back with the Dexron VI answer.

I'm just trying to avoid doing damage to a transmission with 79,000 miles on it. I may go with the Valvoline Dex/Merc you suggested.

 

That was an extract. The full bulletin is here: http://www.revbase.com/BBBMotor/Tsb/...dPdf?id=168779

My trans has 80k+ on it. Most of it's life was the OEM fill. I decided to change the fluid when some shifts would unexpectedly "balk" (around 65k). What I found was that the amount of fluid that came out was considerably less than a full fill - since I don't have any leaks, I am putting it down to evaporation, etc., over the years. Anyway, I decided to go "by the book", i.e. a Dex III - which is incidentally what Tremec (the trans manufacturer) has confirmed is the "correct" fill. There are a number of Dex/Merc fluids out there from the major manufacturer's, usually labelled "for GM and Ford vehicles" needing Dexron III or Mercon. With a "full fill" of the Valvoline, all shifting issues were gone. I did decide to skip "store brands" - cheaper for a reason, in my book.

Anyway, it's only $16.87 at Walmart.

 

Forget the ATF and use this ...



Around 90k, I started getting an occasional grind going into 4th. I swapped the fluid with fresh DexIII and ... nothing changed. Drained the dex crap out and filled with it that stuff, and the grind hasn't returned in 30k miles. You can definitely tell that there's a higher viscosity lubricant in there especially when it's cold, but I actually prefer how it feels now ... smoother, less notchy.

 

What yr is your car???

 

 

Pennzoil Synchro Fluid is their version of the GM fluid that was formulated especially for the GM/Chrysler "New Venture" light truck transmissions.

It does not meet Dexron III.

 

'02

I'm not a mechanical engineer by trade, but when a transmission grinds with fluid A and that grind disappears with fluid B ... personally I'll stick with fluid B. And that transmission now has 120k miles on it. YMMV

And honestly I think the choice to use DexIII had more to do with maximizing power to the wheels and minimizing heat than it did with longevity of the transmission.

 

 

I will add my opinion. I know a lot of people use RedLine oils. The RedLine 30505 D4 ATF is Dexron III and made for the T56. A lot of people swear by it. I am going to try it in my 2002 Z06.