View Poll Results: Which fluid is best for a M12 T56?
Redline D4 ATF
53
8.85%
Royal Purple Syncromax
179
29.88%
GM Syncromesh
154
25.71%
OEM Dexron III ATF
213
35.56%
Voters: 599. You may not vote on this poll
Which T56 fluid?
12 Second Club
Joined: Sep 2005
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From: Bucks County, Pa.
Amber, Joe???
TECH Enthusiast
Joined: Aug 2002
Posts: 521
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From: Los Angeles
I had a kevlar six puck clutch, new pressure plate, new flywheel, and hydraulics. The transmission was refilled with Redline D4. Then the nightmare began. The clutch would not bed-in and the transmission would not shift easily. I had to muscle it into every gear. The Redline was too slick!!! I added some Auto-rx to the fluid. This allowed the clutch to bed-in and for me to shift the transmission. It was still a bit hard. I dumped the Redline and put on Pennzoil Syncromesh. This was a big improvement. It was still tempremental at times but 1000% better than the Redline.
I decided to dump the Syncromesh and put in Mobil 1 AFT. Now, my transmission shifts normally. This is the best stuff that I have used.
I decided to dump the Syncromesh and put in Mobil 1 AFT. Now, my transmission shifts normally. This is the best stuff that I have used.
Staging Lane
Joined: Feb 2006
Posts: 98
Likes: 0
From: FL
MANUAL TRANSMISSIONS AND TRANSFER CASES
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.
and
Use of manual transmission fluid part number 88861800 U.S. (88861801 Canada) in place of Dexron III.
Important Note: If the vehicle owners manual lists Dexron VI as the recommended transmission, transaxle or transfer case fluid disregard any information supplied in this PI. Use eSI and or the vehicle owners manual to determine what type of fluid should be used prior to referencing the below information
Recommendation/Instructions:
Manual Transmission fluid part number 88861800 U.S. (88861801 Canada) is currently available through GMSPO. Current and past model vehicles listed above with either a manual transmission or transfer case that REQUIRE Dexron III should use the above listed manual transmission fluid. This fluid is a direct replacement for Dexron III in manual transmissions and transfer cases. DO NOT use Dexron VI in place of the manual transmission fluid in any manual transmissions or transfer cases as a failure may result.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
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From recent personal experience: do not run Mobil1 synthetic. I did and was forced to change it out two days later as it became harder to get into gear like you would not believe. I made a trip to the local Walmart and bought their Super Tech brand Dexron ATF. The car immediately became easy to shift again and feels great now. There were several articles years ago concerning the T56 and synthetic fluids saying something about the synchros not functioning properly and wearing prematurely when syn was used.
I have my tranny down and need to replace my fluid the problem is i only have 3 quarts of Royal Purple and none of the local auto stores have any RP. Can i use a quart of any other brand along with my 3 quarts of RP?
12 Second Club
Joined: Sep 2005
Posts: 4,273
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From: Bucks County, Pa.
I would go buy 4 quarts of a good name brand Dex 3 mineral fluid before I would put one drop of RP in my T56!! Their Synchromax almost destroyed my gearbox. 
That said, I do like their power steering fluid, and Purple Ice (the ONLY products of theirs that will ever be in my car!).
That said, I do like their power steering fluid, and Purple Ice (the ONLY products of theirs that will ever be in my car!). 
After reading up on all the different fluids and the different experiences in the T56's on this board, I chose to run standard old Dexron III. I change it at every third oil change since it is cheap enough, and have zero problems.
12 Second Club
Joined: Sep 2005
Posts: 4,273
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From: Bucks County, Pa.
Teching In
Joined: Dec 2007
Posts: 1
Likes: 0
Don't know what stuff had my '06 GTO from the factory, but RP Synchromax definitely made an improvement (especially when cold), even at an early 2K miles.
Don't know about early T56s, but don't think ANY fluid is going to damage an LS2 T56 in any way. I think it's just a matter of preference. I might try M1 ATF next time. Later.
JC
Don't know about early T56s, but don't think ANY fluid is going to damage an LS2 T56 in any way. I think it's just a matter of preference. I might try M1 ATF next time. Later.
JC
12 Second Club
Joined: Sep 2005
Posts: 4,273
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From: Bucks County, Pa.
^^^It will be just as good as any other, regular old, mineral based Dex 3 type fluids, and probably MUCH better than the el cheapo, discount/dollar store Dex 3s, and possibly better than the Wal Mart Super Tech Dex 3.
Last edited by dailydriver; May 17, 2016 at 02:31 PM.
It's important to mention if you have stock or carbon blockers in the trans. The normal Dex III doesn't seem to work all that well for me on carbon blockers but on paper I had no issues.