C6 ATF
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6th Gear
Joined: Apr 2023
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C6 ATF
Here's my problem.. I don't know what ATF to use.. My truck is a Frankenstein its a 72 f250 with a 67 hood. A 71 grill.A 400 engine thats from 79 (according to valve covers) and a C6 tranny with no id plate.. The dip stick calls for CJ .. But due to the Hodge podge of mixed matched parts its not hard for me to think maybe a dip stick wasn't replaced at some point in time and that maybe I really need type F. And to make matters worse for every piece of info I find on the net I also find a piece of conflicting info.. So I have two ?'s
1) are the 2 types interchangeable?
2) if not is there 1 substitute for both that will work
1) are the 2 types interchangeable?
2) if not is there 1 substitute for both that will work
Lead Driver
Joined: Jul 2017
Posts: 9,569
Likes: 1,158
From: San Jose, CA
Was the transmission rebuilt by anyone?
If I remember correctly, early C6, transmissions used type-F fluid. Later models, such as would’ve come in a 79 truck, used Dexron fluid.
But the primary driver of fluid type, again, if I remember correctly, is the material of the clutch plates.
Which means a transmission can be built to use either type of fluid.
They are not generally considered compatible or interchangeable, but it’s the clutches that determine what type is used.
if the transmission was rebuilt, check with the rebuilder.
If I remember correctly, early C6, transmissions used type-F fluid. Later models, such as would’ve come in a 79 truck, used Dexron fluid.
But the primary driver of fluid type, again, if I remember correctly, is the material of the clutch plates.
Which means a transmission can be built to use either type of fluid.
They are not generally considered compatible or interchangeable, but it’s the clutches that determine what type is used.
if the transmission was rebuilt, check with the rebuilder.
Logistics Pro
Joined: May 2015
Posts: 4,463
Likes: 954
From: Tri Cities, TN
It does not matter which fluid you use as long as you don't mix them up. You need to drain the trans and the converter and refill it with your choice Type F or Dexron. I always use type F because it has fewer friction modifiers and gives firmer shifts. Back in the day the Chevy guys racing automatics would use Type F to get better shifts.
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
The bolt pattern on a transmission for a 351M and 400 is different from a FE engine. Assuming of course that your truck originally came with a FE. So chances are the trans and engine came from the same truck. 3X 1 Ton and 2X Mark. But, one thing not mentioned yet is during the 1977 model run (the year the 351M/400 replaced the FE) is when Ford switched fluids in the C6. So if your tranny happens to be an early 1977 (you stated Frankenstein) it would have used type F. Of which your dipstick says it takes Dexron. Moral of the story of facts, chances are it takes Dexron. But the only way to make sure is to take a sample to a local research lab that can test it and tell you. If there is an aftermarket fluid that can be mixed with either, I would never use it. There is a lot more to an oil product than what most think. Different brands formulate their fluids different. I would only use a name brand oil product. First choice, Genuine Ford Motorcraft. Second, Valvolene if I have to.
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