Any years ATF for use in GM automatic Transmissions

[Chopper1942]

Anyone who would like to understand the progression of of the fluid in your automatic transmission should watch this YouTube video produced by Weber State University.

https://www.youtube.com/watch?v=8oWFTOY-3tY

This will clear up many questions and posts about what to use in your vehicle.

[Chopper1942]

If you can find Dexron III fluid it will be less expensive to purchase than Dexron VI and will work fine in the older transmissions.

[Cadillac Jack 82]

Use Dexron/Mercon III which can be found at any parts store.  The newer stuff will work but its too thin for those older transmissions from the late 60s and earlier.

[Chopper1942]

Actually all of the fluids today are thinner (lower viscosity) than the fluids used in the old Hydramatic transmissions. Until about 1946-1947, the Hydramatic transmissions used 30W motor oil in the summer and in the winter in colder climates it was changed to 20W.  Because of the high temmperature in the transmission, the motor oil had to be changed often. The motor oil easily oxidized and would sludge up the transmission.

In about 1946, GM specified only Hdramatic Fluid be used in the transmission and it was only available at the dealership. In the owner's manual for these cars, it stated that if you needed to top off the transmission fluid, you could substitute 20W motor oil, but it should be drained and the transmission filled with Hydramatic Fluid as soon as possible.

[PHIL WHYTE CLC 14192]

Great video, thanks for that. I'll carry on using dexron 3 in my 54 CDV, even though its not licensed by GM anymore.

[Lexi]

Yes, I agree with Phil it was a great video. Thanks for posting Chopper1942. Clay/Lexi

[64\/54Cadillacking]

Have you guys ever used the Rislone Transmission Stop Leak/Slip fluid before?

Or even the Lucus transmission stop leak transmission fluid as an addition to the regular Dexron III fluid that's already in your transmission now?

Reason being is because those 2 fluids are very thick and might work better in our old hydramatics than standalone ATF.

As a matter of fact, I'm going to buy some for my '54 today and see if it will help reduce the serious ATF leak that I have.
 

[TJ Hopland]

The Lucas stop leak is so thick you can't even pour it if its below about 50*F so I would think mixing it in would have to at least slightly thicken things up. 

[64\/54Cadillacking]

The Lucas stop leak is so thick you can't even pour it if its below about 50*F so I would think mixing it in would have to at least slightly thicken things up. 

I believe this could help with rough 2-3 shift points and possibly stop or at least slow down leaks from these transmissions. If worst comes to worst, you could always simply do a drain and refill with straight Dexron III during the winter season. If anything, you'd probably want a slightly thicker fluid circulating in these old Hydramatics for added protection especially since I believe the Type A whale oil fluid was much thicker than Dexron III (which pours in like water) so it makes sense having higher viscosity ATF in the unit for smoother shifts all around.

One bottle of the Lucas shouldn't hurt anything, from watching that very informative video above, The Suffix "A" transmission fluid was equivalent to a 30W motor oil.

The problem with all the early thru the mid 50's hydramatics is that heat destroys them. Since there's no external cooling for the transmission fluid, the fluid would burn up rather quickly thus the laughable low fluid change intervals of the time.

It's interesting how GM was constantly revising the fluid it seemed like on a yearly basis to improve and prevent the rapid wear from not just the Hydramatic trans, but the Power and Turbo Glide transmissions as well. Eventually when Dexron first came out, it really helped cut down on transmission fluid change intervals and extended the life of all GM transmissions. But once Cadillac finally sent the transmission fluid to the radiator for cooling, and the introduction of the TH400 trans, it eliminated a lot of premature destruction of its transmissions that was also helped out with the introduction of Dexron at the time. .

[Chopper1942]

The cause of the hard 2-3 upshifts and 3-2 downshifts is twofold. First is the design of the transmission.

1. In 2nd gear the front unit band is released and the front clutch is applied and in the 2nd unit the rear band is
   applied.

2.  In 3rd gear the front unit band is applied and the front unit clutch is released while the rear unit band is
    released and rear cutch is applied.

3.  Because the transmission is releasing and applying 2 bands and clutches at the same time, the timing has to be
    perfect to have a good smooth shift.

First, adjust the throttle linkage. Throttle linkage adjustment must be spot on.  This controls pressures inside of the transmission and the shift points.

Second, perform an internal band/servo adjustment.

If these are done correctly, it will greatly improve shift performance. It will never shift a smoothly as a Turbo 350 or 400. In these units each shift was made by applying a clutch pack. No bands applied or clutches released.

Now back to the additives.  Draining the fluid coupling and droppping the pan (must be done to perform the band/servo adjustments) and filling with Dexron III is the best option.  The lower viscosity will improve the application and release of the bands and clutches.  Also, the better lubricity makes for smoother application.

Another thing to remember is that the fluid change intervals listed for Dexron III is for vehicles that had external transmission fluid coolers.  Your Hydramatic does not and will still generate high fluid temperatures.  The Dexron III's additive package can tolerate higher temperatures before oxidizing unlike the older fluids. But, you still should change it more often, maybe 10K-20K.