trans fluid type?

[harmony]

I've just discovered that my 48 Chrysler that has a fluid drive coupler actually has ATF in the transmission.  I spotted a drop on the bolts on the end and it seemed to be a bit redish in colour.  I was checking the level and sure enough it seems to be a bit red.  But not a deep red.  But quite clear and not dirty at all.  So Perhaps it was filled with ATF  at some point and the topped up with 10W  down the road.  So that might explain why it's not a dark red.  I used my baby finger as a dip stick and I couldn't smell that distinctive ATF smell either.  I'm curious if 10W and ATF like each other?

Having said all that, it seems to operate fine.  But with this new discovery, I'm temped to drain the trans and refill it with 10W.  Is it necessary to make sure all the ATF is out of the trans?   Should I but a few miles on it after I fill it with 10W and then drain that out and fill with new 10W again?

Cheers 

[keithb7]

The Mopar semi auto transmission oil spec is 10W motor oil. ATF, (automatic transmission fluid) with red dye is also generally a 10 weight oil.  When speak of weight, we generally referring to the viscosity rating. How well the oil flows in various temperatures. ATF and engine oil have a very different additive package. ATF oil is dyed red so we can easily distinguish the difference between it and engine oil. Engine oil is designed to work in very toxic environment. Crank cases fill up with by-products of combustion. Both gases and particles such as soot are found. Condensation, unburnt fuel, lead, dust from the environment, and more. It's nasty in there. Modern detergent engine oils are designed to trap, carry, and suspend all the crap in the engine crankcase within the oil. The transmission runs in a much more controlled, cleaner environment.  ATF has special friction modifiers added for wet clutch and brake band parts. Engine oil does not.  Your semi auto tranny has no wet clutches or brake bands inside it.

 

Both the ATF and the 10W engine oil will work in your semi-auto transmission. The engine oil is all that is called for, likely because it does not need all the additives found in ATF. Engine oil is cheaper and more often readily available in ones garage or trunk. The additive package in engine oil won't hurt your tranny either. You can use either. Mixing the two? I don't know what that can lead to. Personally I'd run one or the other. Not mix them.

Edited April 11, 2020 by keithb7

[harmony]

15 minutes ago, keithb7 said:

The Mopar semi auto transmission oil spec is 10W motor oil. ATF, (automatic transmission fluid) with red dye is also generally a 10 weight oil.  When speak of weight, we generally referring to the viscosity rating. How well the oil flows in various temperatures. ATF and engine oil have a very different additive package. ATF oil is dyed red so we can easily distinguish the difference between it and engine oil. Engine oil is designed to work in very toxic environment. Crank cases fill up with by-products of combustion. Both gases and particles such as soot are found. Condensation, unburnt fuel, lead, dust from the environment, and more. It's nasty in there. Modern detergent engine oils are designed to trap, carry, and suspend all the crap in the engine crankcase within the oil. The transmission runs in a much more controlled, cleaner environment.  ATF has special friction modifiers added for wet clutch and brake band parts. Engine oil does not.  Your semi auto tranny has no wet clutches or brake bands inside it.

 

Both the ATF and the 10W engine oil will work in your semi-auto transmission. The engine oil is all that is called for, likely because it does not need all the additives found in ATF. Engine oil is cheaper and more often readily available in ones garage or trunk. The additive package in engine oil won't hurt your tranny either. You can use either. Mixing the two? I don't know what that can lead to. Personally I'd run one or the other. Not mix them.

Thanks for the details of ATF.   I should have been more specific when I said 10W.  I actually meant 10W engine oil that was non detergent  as the manual calls for.  Was ATF fluid even invented back in 48?  As we know there is that metal sign on the trans spcifically saying to use 10W non detergent oil.  

My thinking in draining the fluid is because it may be mixed,  But like I said it seems to function fine.  

[greg g]

For piece of mind, drain and replace with sae10.  Somebody probably toped it off with atf, because, well it's a transmission ain't it???... But it doesn't hold a lot any way so the AMT of atf is probably small, but for the cost time and effort, drain and replace with spec lube seems to be the way to go.

[harmony]

4 hours ago, greg g said:

For piece of mind, drain and replace with sae10.  Somebody probably toped it off with atf, because, well it's a transmission ain't it???... But it doesn't hold a lot any way so the AMT of atf is probably small, but for the cost time and effort, drain and replace with spec lube seems to be the way to go.

I agree

[Dodgeb4ya]

Mixed fluids wouldn't damage anything in a M4,5 or 6 transmission. It's all just constant steel mesh gears and and has a steel mesh screen to collect metal filings. Nothing special.

But yes as mentioned drain it all out and put the new 10W in.

[Dan Hiebert]

No, ATF as we know it now had not been invented in '48.  10w oil is just that, thin oil.  Principle additives to ATF are to prevent foaming in (duh) automatic transmissions, protection so the heat ATs generate doesn't break the fluid down, and some have additives to swell modern seals to prevent leaks (Type F comes to mind).  None of those additives will harm the fluid drive system, although some will argue that the swelling properties will ruin fluid drive seals.  Our fluid drive units did/do not have foaming issues, so that's an unneeded but harmless additive.  Oil does break down over time, though, so the unit shouldn't go forever without a fluid change, but you'll still see clear oil when that time comes, so don't be fooled because you don't see dirty oil.  As Dodgeb4ya notes, mixing won't hurt a thing, although most here will champion one or the other, with factory spec preferred.     

[Dodgeb4ya]

Yep as mentioned above...

But....I never mix types of / or even brands of oils on my cars

and trucks.

I've rebuilt/repaired quite a few of these goofy transmissions and broken the rules as for the required 10 W oil.

Re-did a M5 trans for a friends old beater daily driver the "Blue Blaster" a 1948 Windsor cpe.

He ran 10/30 in the M5 trans for almost 5 years and said he liked the way it

up-shifted so fast.

I have 20W in my 1946 NewYorker 3 cpe. Works fine.

I like to see what happens if I experiment with things just to learn.

I would not tell anyone else to try these oil options though.

Do what the factory shop /owners manuals tell you!?

 

[harmony]

Thanks again guys for all the info.  Just the last few day's I've noticed that it "sometimes" resists going into high range.  It has a mechanical feel about it. Like there is a bit of binding in the linkage, but most of the linkage joints are metal on metal or a couple have a rubber bushing.  They all seem to be fine and clean and I sprayed them with silicone spray lubricant.  But no grease nipples except the two on that long tube shaft, plus one other. .  With a slight extra pressure on the shift lever it slides into high range.  It only happens one out of 10 times maybe,  and I don't think it matters if the car has been run for awhile.  However I rarely go for drives more than an hour at a time anyways right now.

[greg g]

Thanks for the update.  Check all your electrical connections associated with the trans.

[Richard A]

I wouldn't want ATF in my gearbox, but as I recall Dex3 was an "acceptable" fluid in the fluid coupling. As I recall AW32 fluid was also acceptable in the fluid coupling, but do your own research. I wouldn't take that as gospel without checking.  It's been too many years ago that I had to research it.

[Loren]

There are lots of older transmissions that specified ATF as the lubricant of choice, Mercedes comes to mind.

ATF has cleansing effect on the insides of a gearbox that Gear Oil doesn't have. When I was going to rebuild a transmission, I used to drain the 90wt and refill with ATF.

Then put several hundred miles on it before opening it up. The insides were always razor clean! Sometimes this inside cleaning made an overhaul unnecessary.

The early SAABs had a sprag clutch freewheeling device. It was absolutely necessary on a two stroke but its use was optional on the four stroke engine. If they went unused for long periods of time they would collect gummy dirt and slip when you did try to use them. Most of the time mechanics would pull the transmission and make a big expensive deal out of it. I could change the lube and have it working perfectly in one trip around the block.

SAAB hunted around for better lube for years. They found out that lighter oil actually lowered the operating temperature. They went from 90wt to 75wt which was like water. Sometime later they gave up on 75wt as it was too hard to find and settled on 30w Motor Oil. They didn't care if it was non-detergent or anything like that. You could use the same stuff you put in the engine.

Current manual transmissions are using rather thin fluid which is supposedly very high tech. (and priced wildly high too) ATF is undergoing some changes too, and that's making it pricey as well. Standard old ATF is more than good enough for a manual transmission. If you're paying $15 a quart you're buying the wrong stuff.

So will ATF (such as type F or Dextron) work in a FluidDrive coupling? Of course. Will it attack the seal? Now that is an unknown. If I had a FluidDrive car (and a spare coupling) I'd sure try it. That's not really a good test as if it fails it might have been on its last legs anyway, but at least it will be very clean on the inside. lol