Hello, I know the th400 is no fancy modern transmission and is pretty lenient on whatever atf you want to put in it but i have a few questions. The current fill is castrol transmax dex/merc. My walmart stopped carrying it so I was thinking about some other atf options. I see that dex 6 is compatible with previous dexron fluids. I know that dex 6 is thinner but is more shear resistant than dex 3. I dont put many miles on my truck per year. How fast does dex 3 shear compared to dex 6? I am a little concerned about the viscosity of dex 6 but if dex 3 shears below dex 6 quickly then dex 6 would be better. How does dex 6 compare to dex 3 as far as friction modification? I would like to keep the atf grippyness the same as dex 3. I read that allison didnt want dex 6 in their allison 1000 because of seal compatibility. I am pretty sure my th400 is original from 1978. Would i have any seal or clutch friction issues using dexron 6? Also how would the clutches do being soaked in a conventional atf and now being submerged in synthetic? Thanks guys, just trying to see how similar dex 3 and dex 6 are and if its a good fluid for an old th400 that sees mostly street driving and occasional plow duty in the winter.
Questions on th400 trans fluid options.
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GM specifically says Dexron VI is good for all GM automatic transmissions. Maxlife is the best value. Use it with confidence
The coefficient of friction is the same in Dexron 6 vs Dexron 3.
Mineral based DexronIII would be well below a Dexron 6 after 30,000 miles, the actual overtake would be much sooner but in no time it could be down in the 5 cSt range. Dexron 6 is much more shear stable and a total replacement for Dex3.
The primary makeup of DexronVI is group 3 oils, so it's just a highly refined mineral oil, there is no harm in adding it into a transmission for Dex3.
That being said i do personally recommend and use Maxlife LV Dex/Merc over Dexron 6, although both are top choices for Dex 3, the Maxlife is just using a very nice additive package and a total bargain when you buy it in gallon jugs for around $16.
A little more technical information from a triblogist here.
https://bobistheoilguy.com/forums/ubbthreads.php/topics/3014880/Improvements_in_DexronVI_over_
Mineral based DexronIII would be well below a Dexron 6 after 30,000 miles, the actual overtake would be much sooner but in no time it could be down in the 5 cSt range. Dexron 6 is much more shear stable and a total replacement for Dex3.
The primary makeup of DexronVI is group 3 oils, so it's just a highly refined mineral oil, there is no harm in adding it into a transmission for Dex3.
That being said i do personally recommend and use Maxlife LV Dex/Merc over Dexron 6, although both are top choices for Dex 3, the Maxlife is just using a very nice additive package and a total bargain when you buy it in gallon jugs for around $16.
A little more technical information from a triblogist here.
https://bobistheoilguy.com/forums/ubbthreads.php/topics/3014880/Improvements_in_DexronVI_over_
Maxlife
MolaKule
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Originally Posted By: 901Memphis
The coefficient of friction is the same in Dexron 6 vs Dexron 3.
Mineral based DexronIII would be well below a Dexron 6 after 30,000 miles, the actual overtake would be much sooner but in no time it could be down in the 5 cSt range. Dexron 6 is much more shear stable and a total replacement for Dex3.
The primary makeup of DexronVI is group 3 oils, so it's just a highly refined mineral oil, there is no harm in adding it into a transmission for Dex3.
That being said i do personally recommend and use Maxlife LV Dex/Merc over Dexron 6, although both are top choices for Dex 3, the Maxlife is just using a very nice additive package and a total bargain when you buy it in gallon jugs for around $16.
A little more technical information from a triblogist here.
https://bobistheoilguy.com/forums/ubbthreads.php/topics/3014880/Improvements_in_DexronVI_over_
The TH400 is a good transmission and we modifiy it for use in racing transmissions.
Disregard the Allison issue as it is not germane to your transmission.
The coefficient of friction is the same in Dexron 6 vs Dexron 3.
Mineral based DexronIII would be well below a Dexron 6 after 30,000 miles, the actual overtake would be much sooner but in no time it could be down in the 5 cSt range. Dexron 6 is much more shear stable and a total replacement for Dex3.
The primary makeup of DexronVI is group 3 oils, so it's just a highly refined mineral oil, there is no harm in adding it into a transmission for Dex3.
That being said i do personally recommend and use Maxlife LV Dex/Merc over Dexron 6, although both are top choices for Dex 3, the Maxlife is just using a very nice additive package and a total bargain when you buy it in gallon jugs for around $16.
A little more technical information from a triblogist here.
https://bobistheoilguy.com/forums/ubbthreads.php/topics/3014880/Improvements_in_DexronVI_over_
The TH400 is a good transmission and we modifiy it for use in racing transmissions.
Disregard the Allison issue as it is not germane to your transmission.
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The TH 400, C6, and TF 727 were probably 3 of the best AT ever built. The TH400 does real well on Amsoil or Mobil 1 ATF. This unit doesn't need a low viscosity fluid, fuel efficient they are not.
Originally Posted By: Trav
The TH 400, C6, and TF 727 were probably 3 of the best AT ever built.
Having owned all of these transmissions, I'll second that. Especially in an automatic transmission tow rig.
The TH 400, C6, and TF 727 were probably 3 of the best AT ever built.
Having owned all of these transmissions, I'll second that. Especially in an automatic transmission tow rig.
Originally Posted By: Trav
The TH 400, C6, and TF 727 were probably 3 of the best AT ever built. The TH400 does real well on Amsoil or Mobil 1 ATF. This unit doesn't need a low viscosity fluid, fuel efficient they are not.
Absolutely not, agreed! We used TH400 short case versions in Camaros in the 70's, they fit very well in a Trans Am too. Nearly unbreakable. We would crank up the pump pressure so high we occasionally burst cooler hoses.
Want hard shifting? Mix in some type F.
And we also agree that ML is fantastic stuff, I would strongly consider it.
The TH 400, C6, and TF 727 were probably 3 of the best AT ever built. The TH400 does real well on Amsoil or Mobil 1 ATF. This unit doesn't need a low viscosity fluid, fuel efficient they are not.
Absolutely not, agreed! We used TH400 short case versions in Camaros in the 70's, they fit very well in a Trans Am too. Nearly unbreakable. We would crank up the pump pressure so high we occasionally burst cooler hoses.
Want hard shifting? Mix in some type F.
And we also agree that ML is fantastic stuff, I would strongly consider it.
Supertech DexVI
I agree with Steve SRT8. I have run Type F in the TH 400 in my big block Chevelle. If you want crisp, firm shifts the Type F is your solution. The Dex VI and III work fine , but are noticeably "softer" if high throttle shifting is your requirement. I use Magnefine remote filter plus small external cooler. I have broken u-joints and yokes, but never the trans. Very tough units.
My 1990 Jaguar XJS V12 has a GM TH400 transmission and it shifts like silk with Maxlife ATF...
I might pick up some mobil d/m atf. I see its a tes-389 fluid. i run a large atf cooler with an atf temp gauge on the output line from the trans. I only put a couple thousand miles on the truck per year and the atf only gets to about 200f when plowing and 160-180 when driving around in the summer.
Originally Posted By: zeng
That's fantastic temperatures you've .....
I think i run the tru cool lpd 4590 cooler in front of my radiator. It does work very well considering the low temp on the output side. The trans will heat up when plowing but once it reaches around 200 the cooler in the radiator stops heating the oil and starts to cool it so i usually stays around 200.
That's fantastic temperatures you've .....
I think i run the tru cool lpd 4590 cooler in front of my radiator. It does work very well considering the low temp on the output side. The trans will heat up when plowing but once it reaches around 200 the cooler in the radiator stops heating the oil and starts to cool it so i usually stays around 200.
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