Always posts asking about what's the best trans fluid. Is there any bad transmission fluids to stay away from? Are there any documented failures from someone using a particular trans fluid?
What's the worst trans fluid to run?
Eman85
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Take care. Tom Worthington
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Just use water.... ?‍♂ WTF
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Water will work, just not very long.
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Guys are saying to use the Alison Tran Synd synthetic fluid. The Alison behind a relative's 8.1 says to use Dexron VI. Are the transmissions that different, that the gasser uses Dexron VI, and the diesel uses the Tran Synd? Also I've read that Alto clutches and Raybestos steels, do not like synthetic fluid. Any truth to that? Finally are there two versions of Dexron VI, mineral and synthetic?
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It might have something to do with seal compatibility. Apparently Dexron VI is not recommended by Allison in certain transmissions (depends on the S/N) --> "...DEXRON-VI caused Viton (FKM, fluoroelastomer) seals to harden and crack". But, this would only apply to Allison transmissions.
Ref:
Former Allison Transmission Fluids Engineer (Mr. TranSynd)
Hello to all on this forum. My name is Tom Johnson and I was the Transmission Fluids Engineer at Allison Transmission from 1990 until my retirement in 2009. Since my retirement from Allison, I'm free to engage in these forums and set some things straight and answer any questions you might have...
www.duramaxforum.com
Former Allison Transmission Fluids Engineer (Mr. TranSynd)
Hello to all on this forum. My name is Tom Johnson and I was the Transmission Fluids Engineer at Allison Transmission from 1990 until my retirement in 2009. Since my retirement from Allison, I'm free to engage in these forums and set some things straight and answer any questions you might have...
www.duramaxforum.com
Lots to read here: Former Allison Transmission Fluids Engineer (Mr. TranSynd) - Chevy and GMC Duramax Diesel Forum
And here: Transynd vs. Dex VI
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From the above article link posted by the allison engineer :
welcome.
![Image]()
and to settle this, in the 2006+ year models, are you supposed to run dexVI? or what.
i run transynd but others have debated forever.
so what's your professional opinion?
Dmaxryan10,
Allison published S/N cutoffs for transmissions with DEXRON-VI compatible seals. However, Allison no longer recommends DEXRON-VI for any of their products. TranSynd, or one of the other TES-295 fluids, is the best answer.
welcome.
and to settle this, in the 2006+ year models, are you supposed to run dexVI? or what.
i run transynd but others have debated forever.
so what's your professional opinion?
Dmaxryan10,
Allison published S/N cutoffs for transmissions with DEXRON-VI compatible seals. However, Allison no longer recommends DEXRON-VI for any of their products. TranSynd, or one of the other TES-295 fluids, is the best answer.
I have been using it for years. Zero issues and when I have taken the trans apart it's always clean. I like to run 303.in all of mine.
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When I was working in the test cells at Allison, we did not like Dex-6. It attacked the seals. But, that was the approved trans oil for the Allison transmissions that were installed behind the 8.1L gas and Duramax engines in the 1-ton trucks at the time. If I recall, we had for about a year before it was phased out and replaced with TranSynd.
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Why in the world would dex-6 "attack" seals in an allison but be fine in over a million other transmissions?
Not calling anyone a liar...just hoping someone can explain it to me
Not calling anyone a liar...just hoping someone can explain it to me
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Seal composition.
Viton composition solved the leak issues.
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Lots of hate for Type F. Note that not all Type F fluid is created equal. The one I use has a good bit of anti-foaming, a high flashpoint, and doesn't "coke" at all.
The worst trans fluid is no trans fluid.
The worst trans fluid is no trans fluid.
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Which one is that? Take care. Tom Worthington
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I have to ask this after reading all these replies.
We have only used Castrol DEX/MERC in our Turbo 400.
Reverse manual, trans brake, brass screen, 8" converter ~6000, ~725HP. see sig.
We have an ERPM flair on the 1-2 shift that I addressed here late in 2018. The air shifter is set to 6600, ERPM peaks at 7500.
Is the Castrol DEX/MERC an acceptable fluid for our application??????
I installed a RP trans pressure sensor (driver side port) since then but we didn't run the car in 19. Getting ready to run the car this year and I could change out the fluid if it would help. It could be another issue though.
Thanks
Tom
We have only used Castrol DEX/MERC in our Turbo 400.
Reverse manual, trans brake, brass screen, 8" converter ~6000, ~725HP. see sig.
We have an ERPM flair on the 1-2 shift that I addressed here late in 2018. The air shifter is set to 6600, ERPM peaks at 7500.
Is the Castrol DEX/MERC an acceptable fluid for our application??????
I installed a RP trans pressure sensor (driver side port) since then but we didn't run the car in 19. Getting ready to run the car this year and I could change out the fluid if it would help. It could be another issue though.
Thanks
Tom
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