Best transmission fluid for TH400

Houtan

Member
Hi everyone,

I want to change TH400 transmission fluid in my 1974 GS 455 Stage 1, There is Dexron II D, Dexron III G and Dexron VI available here, Dexron III has lover viscosity than original Dexron II and Dexron VI is even lower, My question is what is my benefit on going for lover viscosity and what I will lost on them?
 
in general, lower viscosity means less power loss. enough so that you'll notice? probably not. newer blends also typically have less of the dino / bio fuel oils ( the original Dexron II used Sperm Whale oil, which required a D-II reformulation because the US banned importation of Whale Oil ) and more custom synthetic additives.

otoh, your trans wasn't designed for the lower viscosity and may not have adequate lubrication for the clutch plates with the newer blend. also, thinner blends are more likely to leak.

GM ratified Dexron III as fully backward compatible for earlier applications but did not do so for Dexron VI. so i definitely wouldn't recommend Dexron VI.

many of the aftermarket lubrication companies such as AMSOIL will also have recommended blends for the TH-400, that's been used in performance applications for decades now.
 
Thanks bob,

I guess the Dexron B or later formula (Type A etc.) have sperm whale oil additive and from 1973 sperm whale oil was banned in the US and Dexron II C is new formulation for 1973. They used some herbal oils like Jojoba as additive on them. Dexron II C had corrosion problem and they change additives again on Dexron II D on 1975 and also they change additive formula again on Dexron II D on 1978... so I guess every Dexron II D specification on the world are according to 1978 version of Dexron II D.
 
Back
Top