The Chrysler service bulletin says Type F or Type FA automatic transmission fluid...is that what you guys use?

Racers back in the day used it I think because of the heat transfer, fluid compaction(none) and high viscosity rather than the thick sludgy, stinky straight 80 or 90.
Because it is a gear box, I would recommend straight 80(The same for the diff.).
Like all petroleum products after heated up to temp. it will become very viscous so there won't be as much "Fluid/power loss". The dynamic seals will not act differently with either.


The Mopar Junky

Use 90 weight gear oil,my friend did what the book said,and it cost him two 4 speed transmissions. The front bearing in one came out in peices. ATF may be ok in northern Alaska,but not down here.

use the ATF recomended by Mopar. Thats what was in that tranny when new. It's worked fine for 40 years. Mopar knows better what to use seeing they designed it. I've had plenty of 4 speeds and never a failure due to fluid.

90 weight gear oil

At different times MOPAR recommended both ATF and gear oil. The ATF mostly for cold weather areas. Unless you're driving often in 0 degree weather with it I would suggest gear oil. I do believe it provides better protection.

hi
atf-dextron not type f for manuels 1/4 - 1/2 " below fill plug hole !
over fill it and a hot day it expands a little and may be forced out the vent !

Just looked at my 69 mopar shop manuel. SAE 140 for warm climate. SAE 80 or 90 or ATF fluid for cooler climate. So if you live in Florida use SAE 140 if you live in Michagin use ATF. If your in the middle guess. I'm in New England. All the 4 speeds i've had were full of ATF when i drained them and i never had any problems. Every couple of years i changed the fluid and they always worked fine.

myself I'd 1st start w gear oil for the wear protection offered by the "extreme pressure" formulation/additives and if it will work for you as in the shifting quality is acceptable then I would stay with it & if not try
ATF.

I used to use ATF in Winter and 90wt in summer. Very often a blend of the two.

Now Passon has his own formula out that I want to try.

It ought to be worth it.

I ran an 80 OD833 in my 81 short bed that had ATF in it when I got it and I ran it like that for 10 years and it's it still works fine.

As mentioned, ATF tended to be recommended for cold weather and 90 weight or heavier gear lube for hot. Common GL5 gear lube is not friendly to syncros. For 3 season use, suggest SAE 90 GL4 gear lube (hard to find), better yet Redline MT90 gear lube or the Passon fluid. Redline MTL for cold weather.

It does not seem that current ATF formulations are friendly to MT applications and I think the 833 likes a heavier lube.

Resurrecting a 5 year old thread?

I only use gear oil in mine for over 30 years.
Don't fall into the ATF crowd They just haven't had one apart that ate the cluster because ATF doesn't lube well enough for your car. You run your car hard and it needs the correct lube. The guys that say it's OK either have low horsepower or don't whoop on them
Gus

Tractor gear oil, GL3 or GL4.

I'm a gear oil kinda guy myself, never felt good about ATF in a gear box.

I first saw ATF in Mopar stick trannys in 1963. It held up fine in my three speed stick drag cars and Muncie transmissions to.

I agree with Gus.I bought my 65 in 69.The 4speed had gear oil from the factory.Still has gearoil after all these years.Oh yeah it was a daily driver everday for at least 5 years.Ohio winters are cold and never a problem shifting.Rocky

80-90 weight gear oil