[davidgto]

What type AT fluid would you put in original 65 GTO AT?

[Chief of the 60's]

I run Type F in everything from my street cars to my race cars.

[b-man]

Dexron III is what I’d use.

[60sstuff]

Originally Posted by b-man

Dexron III is what I’d use.

Dexron II B, C, D, etc. including the above III as they are all backward compatible.
Just different additives were added throughout the years of Dexron when going through the above letters.

A good read on the ATF is (Dexron - Wikipedia) showing years of use and formulas.

You can still find some of the early versions of Dexron on eBay, or use what b-man suggested.

Chris.

[65 421 TODD]

I'm using Valvoline DEX/MERC ATF in my '65 GTO. The Transmission operates good, shifts nice. And I just bought a case of Castrol Transmax Dex/Merc to keep "In Stock". Check out their websites for descriptions.

[Rich-Tripower]

Originally Posted by Chief of the 60's

I run Type F in everything from my street cars to my race cars.

Type F is what I use in the TH350 in my 69 C10. It was recommended by the company that made the shift kit I put in the trans. It has always worked quite well.

[Chief of the 60's]

Originally Posted by Rich-Tripower

Type F is what I use in the TH350 in my 69 C10. It was recommended by the company that made the shift kit I put in the trans. It has always worked quite well.

All top tranny builders I have dealt with, from Art Carr to Abruzzi to Mike's, all require Type F. I have followed what the known experts say and it has never let me down. There must be a reason for that.

[Sirrotica]

Originally Posted by Chief of the 60's

All top tranny builders I have dealt with, from Art Carr to Abruzzi to Mike's, all require Type F. I have followed what the known experts say and it has never let me down. There must be a reason for that.

The reason for recommendation of type F fluid for GM as well as other transmissions in a high performance application, from what I've been told, is that it's a higher viscosity number than Dexron is at operating temperature. Same as engine oil that is thicker, it raises the operating pressure of the hydraulic circuit inside of the transmission. Type F also does not have friction modifiers that will result in a certain amount of engineered slippage for smoother, less abrupt band, and clutch applications.

Having worked with hydraulic systems in my line of work for many years, thicker fluids definitely raise the operating pressures in the system. Substituting Type F fluid is an easy way of adding more apply pressure to the systems that apply the bands and clutches without modifying the relief valves inside of the transmission. Friction modifiers (same idea that allows posi-traction rears to slip during cornering without chattering) are also omitted from the type F fluid causing less slippage during clutch and band application.

B&M used to sell a branded transmission fluid called "Trick Shift" (they may still sell it), I was told it was just Type F packaged in their own cans. Makes sense that it wasn't a completely different transmission fluid engineered just for B&M, and was just Type F fluid.

Anyway, type F will typically raise pressures in a automatic transmission leading to firmer shifts, and higher apply pressures, causing less slippage, lack of friction modifiers will allow less slippage. Dexron is a fine fluid, just a little thinner at operating temperatures, and has friction modifiers added for smother shifts. I was also told GM used tighter tolerances than ford did when building their transmissions, necessitating a thicker fluid. Dexron used in a typical ford transmission will lead to earlier failures because of the looser tolerances, and addition of friction modifiers promoting slippage, premature clutch and band wear, lower apply pressures causing slippage. These are the reasons I was told that you can use ford in a GM transmission, but not the other way around, FWIW.................

[Chief of the 60's]

Originally Posted by Sirrotica

The reason for recommendation of type F fluid for GM as well as other transmissions in a high performance application, from what I've been told, is that it's a higher viscosity number than Dexron is at operating temperature. Same as engine oil that is thicker, it raises the operating pressure of the hydraulic circuit inside of the transmission. Type F also does not have friction modifiers that will result in a certain amount of engineered slippage for smoother, less abrupt band, and clutch applications.

Having worked with hydraulic systems in my line of work for many years, thicker fluids definitely raise the operating pressures in the system. Substituting Type F fluid is an easy way of adding more apply pressure to the systems that apply the bands and clutches without modifying the relief valves inside of the transmission. Friction modifiers (same idea that allows posi-traction rears to slip during cornering without chattering) are also omitted from the type F fluid causing less slippage during clutch and band application.

B&M used to sell a branded transmission fluid called "Trick Shift" (they may still sell it), I was told it was just Type F packaged in their own cans. Makes sense that it wasn't a completely different transmission fluid engineered just for B&M, and was just Type F fluid.

Anyway, type F will typically raise pressures in a automatic transmission leading to firmer shifts, and higher apply pressures, causing less slippage, lack of friction modifiers will allow less slippage. Dexron is a fine fluid, just a little thinner at operating temperatures, and has friction modifiers added for smother shifts. I was also told GM used tighter tolerances than ford did when building their transmissions, necessitating a thicker fluid. Dexron used in a typical ford transmission will lead to earlier failures because of the looser tolerances, and addition of friction modifiers promoting slippage, premature clutch and band wear, lower apply pressures causing slippage. These are the reasons I was told that you can use ford in a GM transmission, but not the other way around, FWIW.................

The viscosity part I had not heard. The Dextron running hotter and slipping more I have heard. The slipping more part is also why none of them recommend using synthetic fluid either. In fact, they are strongly against it.

Makes sense when you think about it. Why on earth would you want clutches to "slip"?

[Sirrotica]

So I found out that B&M does still sell "Trick Shift" ATF, and as I was told many years ago it is just Type F ATF. It was verified by an inquiry about using it in a ford transmission by the seller.

Question:Will this work as an type f fluid replacement for my c4 trans?

Answer:Trick shift is type f fluid. This was made for your C4 trans. Great stuff!

My source was correct that B&M just has type F fluid packaged with their name on it. That source was also the person that told me that the F fluid is a higher viscosity number, raising line pressure and applying clutches and bands more firmly along with no friction modifiers are added to it, allowing less slippage.

Since I got this information back in the early 70s I've also always used Type F in all my street and race cars, I doubt it makes a huge difference in longevity, but every little bit helps when it comes to expensive overhauls on an automatic transmission.

BTW, the more old fluid you can remove from the transmission when converting from Dexron to Type F, the more effective it is. Ultimately a total rebuild would be the most effective using 100% type F from day one.

[davidgto]

Thanks fellows

[geeteeohguy]

Originally Posted by davidgto

Thanks fellows

Stick with any Dexron/Mercon and you will be just fine.