Chrysler Fluid Drive-Type of fluid

What type of fluid should be used in a 1950 Chrysler fluid drive clutch? Also need to know what level to fill to?

According to the Motors manual that I have it states that you should use the Special Fluid. It does not state what it is though. I just worked on a 48 Windsor that had the same setup and I filled it with DexronII. When you bring the plug around to the inspection hole and remove it, just fill the unit untill the fluid runs out.

Good Luck, Ron

The factory manual calls for 10-W oil. Several trans shops said that either 10-W oil or auto trans fluid would work ok. The amount of oil is another thing. It depends on the system type. Manual says for a sump shared unit takes 10 1/2 quarts.

i would like a straight answer on this also.i have a 52 dodge with the fluid drive 3 speed standerd.i was told straight 30w oil.i was told to bring the converter around to the access hole in the floor and fill it all the way.Is this correct or is there a specified amount?I figured i would check the level since mine seems to slip alot

Do not use 30 oil or transmission fluid. Chrysler recommended their own Fluid Drive fluid (no longer available) or 10W motor oil. Thicker oil will not work better, if anything thinner oil will work better and create less friction drag.

Many of us use TDH tractor fluid, ISO22 or ISO32 grade. TDH stands for Transmission, Differential and Hydraulic. ISO22 is a little thinner than 10W, ISO32 a little thicker. ISO22 probably better but ISO32 easier to get. In any case, not much difference between the 2.

Chrysler never recommended changing the Fluid Drive, just topping it up every 10000 miles if necessary. There is an access plate on the right side of the transmission tunnel directly under the dash board. Remove the plate, you will see the bellhousing with a metal knockout plug. Pry out the plug. Turn the engine by *bumping* the starter until the fill plug comes into view. Stuff a rag around the hole and take the plug out with a socket wrench. The rag is to save you from dropping the plug down inside the bellhousing. Ask me how I found this out lol.

Top up the oil until full. The fill hole is located so you will have the correct amount of air space. As the Fluid Drive is a sealed unit, it must have some air space to allow for heat expansion.

The level is not critical. The Fluid Drive will continue to function if half full or less. In fact this was an early "speed secret". Draining off half the oil gives you the equivalent of a high stall speed torque converter for whippier acceleration. I don't recommend this but never heard of it doing any harm.

The same TDH fluid can be used in the semi auto M6 transmission. It too will take 10W motor oil. There is a pipe plug on the right side of the trans for the fill level and a drain plug on the bottom like any typical manual trans. The oil is supposed to be changed annually or every 10000 miles. Trans can be accessed from under the car or by another removable access plate on the right side of the driveshaft tunnel.

For the Dodge manual trans 90 gear oil (summer) or 80 (winter). Some models use 10W motor oil, the service data book I have is not clear what the difference is or what to use with a manual trans/fluid drive combination. You may need to find a 1952 owner's manual or repair manual for specifics.

The converter might need several quarts but the gear box needs few quarts.

Maybe a better search of this site will provide a proper answer. A fluid drive does not use a torque multiplication coupling !

Heed what Rusty says! 10W motor oil or ISO22 TDH fluid! The fluid drive, each division of Chrysler had its own name for the system, is a fluid coupling ahead of the clutch. It is a straight 1 to 1 coupling, no torque multiplication. I believe it was in 1951 Chrysler introduced the Torque Drive system, it was an extra cost option. Uses a torque converter instead of the 1 to 1 coupling. For cooling purposes the torque converted is in a oil filled housing. The whole thing uses 10W motor oil. Drives the same as the fluid drive. However, cars with the Torque Drive have the words Torque Drive on the original rubber clutch pedal cover.

I nominate Rusty to be the answer chairman for all FD/FTDM5/M6 questions. Round and round it goes!

If they ever catch wise to the search function I am out of a job lol.

Don't worry Rusty they won't!

Hello everyone . I am trying to bring back to life a 1941 Chrysler Royal coupe .I want to keep it all original .Everyone is trying to convince to change the transmission to a newer one . My transmission is a fluid drive .We have gone threw eng. Now we are at transmission . It runs but vacuum shifter came loose and not sure how it goes back. Does anyone know someone that works on these transmissions ? We are in long beach California. Please help .562 5086924

Get a Chrysler shop manual, not a general repair manual like Chiltons or Motors. This transmission is electric shift not vacuum. Hope you took lots of pictures when you were taking the engine apart because the transmission electrics are connected to a switch on the carburetor. The shop manual should have a wiring schematic so you can reconnect everything correctly.

Prewar transmissions were vacuum operated, postwar were electric. On the 41s there were 2 different semi auto transmissions, one for six cylinder and one for eights. My 1954 Motor manual has some information but the factory info would be best. The Imperial club web site has some old manuals. This guy has manuals at reasonable prices. Original, reprint or on CD.

transmission Service Manuals - Shop, Owner, Maintenance and Repair | Faxon

Thank you so much

Prewar transmissions were vacuum operated, postwar were electric. On the 41s there were 2 different semi auto transmissions, one for six cylinder and one for eights. My 1954 Motor manual has some information but the factory info would be best. The Imperial club web site has some old manuals. This guy has manuals at reasonable prices. Original, reprint or on CD.

transmission Service Manuals - Shop, Owner, Maintenance and Repair | Faxon

Thanks a lot for your replie

Here is a pic of a 1942 S10 early vacuum operated M-4. Late 42's had a piston type shift to replace the more trouble some vacuum type shifter.

Rusty is very knowledgeable about fluid drives compared to the average car guy. However, on the subject of what fluid to use I think his information is only partially accurate. In particular, the comments about not draining and refilling the coupling as well as using a generic ISO fluid. Read below why I think those recommendations are not good ones.

In 2009 I did some research, which took a year, and did a short write up on it. I am posting a copy below for those who have an interest in such things.

Best, James

*************************************

Technical Note on MOPAR Fluid Couplings

(Fluid Torque Couplings are NOT covered by this Technical Note)

By James Douglas – San Francisco

Having run several types of oil in MOPAR “Fluid Couplings” over the years and heard many recommendations, I decided to see if I could approach the issue of what lubricant to use in one of MOPAR’s Fluid Couplings by a more scientific method.

As is well known, Chrysler instructed all owners to use “MOPAR Fluid Drive Fluid” only in their Fluid Couplings. Problem is, MOPAR stopped making it decades ago.

My first stop was Chrysler Historical. After a month of looking, I was told that they do not have any of the original engineering information as to the specifications of the fluid.

Then I headed off into internet land to hunt down anything I could find on the subject from ORIGINAL sources. I managed to find an original Chrysler Question and Answer sheet from 1939 about fluid drive from Chrysler Engineering. In it they stated:

“…The proper fluid is a low viscosity mineral oil, which also servers to lubricate the bearing enclosed in the coupling. The pour point is such that the oil will pour at the lowest anticipated temperature, and has no corrosive effect on the steel parts of the unit.”

All well and nice, but not enough to figure out exactly what they used as fluid. Later in the same document they talk about the types of metal used and the carbon-graphite seal. Hum, carbon-graphite seal.

I did some more digging for a few months and turned up a can of unopened original MOPAR Fluid Drive Oil.

An analysis of that oil, and some more literature I ran across, stated that the original fluid was a pure-base mineral oil with a Saybolt Viscosity of between 100 and 150. The fluid had a Viscosity Index of greater than 80.

The fluid had anti-foaming and anti-oxidation additives. It specifically did NOT have any seal swelling agents as these can attack the carbon-graphite seal and the copper in the bellows. This last specification eliminates most modern transmission fluids.

After finding several formulas to convert Saybolt Viscosities to Kinematic Viscosities, it appears that the best match to the original specification is ISO 22 or ISO 32 oil.

However, the ISO 22 is just below 100 Saybolt and the ISO 32 is much higher than 100 Saybolt.

Based on a period (c.1947) Lubrication Industry article on fluid couplings that had the following admonishment:

“Contrary to popular supposition any attempt to use a higher viscosity fluid would actually reduce the torque transmitting ability of the coupling since torque-transmission is dependent upon a high circulation of fluid between the impeller and runner and is not caused by any viscous drag between the two.”

During my continued research on the history of the Fluid Coupling, I ran across the fact that the original company that licensed the fluid coupling technology to Chrysler is still in business and still making fluid couplings for industrial applications.

After a couple of weeks of digging, I found a senior engineer from that company that would have a long technical talk with me on fluid couplings. In essence, he agreed with the period information I quoted above. He added that the lowest viscosity oil that would still provide for bearing lubrication is the one to use in theory. However, he did say that unless the fluid coupling bearing has been replaced and is know to be very high quality then err on the heavy side viscosity wise. Just don’t over do it, he stated.

I was also told that normal hydraulic fluid does not have large amounts of anti-foaming agents in them as they usually do not have large amounts of air in the systems to foam in the first place.

A fluid coupling is only filled to 80% and as such has lots of air in it.

Therefore, when looking for fluid coupling oil, one must look for an oil that is a “Circulating Oil” which has a lot of anti-foaming additives in it.

I was also informed that the additives tend to have a shelf life in the can, or in use, of 5 to 7 years and it should be changed at that time.

I was also told that the couplings are actually somewhat permeable and water vapor will work its way into and then back out, when hot, of a steel fluid coupling. Very little amounts, but apparently is does go on.

I was also told to never use engine oil or ATF as both would cause problems in the long run.

Based on the research and discussions I have come to the conclusion that ISO 32 hydraulic oil with the proper additives and VI (Viscosity Index) above 80 is a suitable replacement for the original MOPAR fluid drive fluid. ISO 22 would be a better exact match, but only if the quality and condition of the bearing is know in a particular coupling.

The oil I have identified that meets the specification, with a higher general viscosity to deal with the age of the bearings, is: Mobile DTE light circulating oil ISO 32. This oil is available at Granger.

I have run this oil for about six months in San Francisco city traffic as well as up steep mountains on very hot days. The coupling works well. I have noticed, and other car people have as well, that the car seems to move out from a dead stop to 10 MPH better with the fluid. Only a before and after session on a dynamometer would tell for sure, but I feel that it moves out much faster.

Classic car owners are advised to use this information at their own risk. I am not a fluid coupling engineer, a bearing engineer, or a lubrication engineer. I have done my best to find out what was in the original MOPAR Fluid Drive Fluid. This effort is in essence industrial archeology and should be carefully considered prior to use.

Wow. Great write up. VERY informative. Thanks!

Thanks for the information. Not changing the oil comes from Chrysler's own publications of the late 40s - early 50s. It is not my idea. But I don't think they had any idea we would still be using them 60 or 70 years after they were made. An oil change couldn't hurt if you use the correct oil.

The TDH oil recommendation came from this forum. Other, more experienced Chrysler owners used it and recommended it, and it seemed the most suitable replacement for the Chrysler Fluid Drive oil. It's good to know I wasn't wrong.

I knew the ISO22 was closer to the original spec but ISO32 is easier to get. The thinner kind is not always available, the ISO32 seems to be fairly standard around the country.

Have also been told that an old speed secret is to drain off up to half the oil. This gives the same effect as a high stall speed torque converter. I have never tried this. Would be interesting to hear the engineer's take on this.

How does the TDH tractor fluid compare? Is it a good second choice if the DTE isn't available?

Rusty, I have not been on this forum for a while. But I got a question from it so I dropped on to answer it....

I did find a little book last year made by Gyrol on fluid drives. It goes into a little detail about the fill level and the stall speed. Draining half the oil would not be a good idea. A change of 10% is al I would do up or down. Remember that the fluid coupling has no stator. Therefore it will never work like a torque converter. There is never any torque multiplication. If ones fills it up to much, then there is no room for expansion when it gets hot and it will explode.

By changing the fill level, you shift the RPM when it locks to 1 to 1. You never change the torque curve just the RMP point when it does.

Tractor fluid does not, I am told, have the extra VI and Circulating additives. Also, I am told by Gyrol that they break down after about 5 to 7 years and that a coupling should have the fluid drained at that interval. The Mobile DTE can be had via Granger. It is a little pricy however. You pay for those additives.

James.

I have recently acquired a 1949 De Soto and appears the Mopar Fluid Drive fluid may be low. Is there an update to the previous forum blogs on the availability of replacement fluid? 

Use the Mobil  DTE ISO 32 light circulating oil.

Available at Grainger.

on the M6 that i owned it had a leak. i used hydraulic jack oil. it was easy to get and was non foaming.it always worked fine.   dennis 

I have a 1942 Chrysler Windsor Highlander with the six cylinder and want to drain out the ATF in the fluid drive and replace it with the Mobil  DTE ISO 32 light circulating oil. Should I simply drain and refill or do I need to flush with something else. Please keep in mind that the mobile oil is very expensive.

If you are talking about the transmission, I drained mine and flushed it w/ kerosene. I then refilled with 10w engine oil.  I drained my fluid clutch and refilled it with ISO 32. I did not flush the clutch.

I see that all the talk on here about using 10W motor oil in the fluid drive unit, but nobody mentions that it has to be non-detergent oil. Maybe some newcomers to the discussion don't know this, so I wanted to mention it. 

@24Chry48 Yes, I did fail to mention that I did use non-detergent oil. Very hard to find locally, Tractor Supply in Viroqua Wisconsin did have some. Thank you for clarifying that fact.

Jeff, 

On 4/4/2023 at 12:09 PM, Jeff Perkins / Mn said:

If you are talking about the transmission, I drained mine and flushed it w/ kerosene. I then refilled with 10w engine oil.  I drained my fluid clutch and refilled it with ISO 32. I did not flush the clutch.

On your fluid drive or clutch, did you have ISO 32 in it before you drained and refilled or was it automatic transmission fluid or something else because I'm wondering if it depends on what was in there that determines whether it needs to be flushed or not.

On 12/13/2014 at 12:03 AM, James_Douglas said:

Rusty, I have not been on this forum for a while. But I got a question from it so I dropped on to answer it....

I did find a little book last year made by Gyrol on fluid drives. It goes into a little detail about the fill level and the stall speed. Draining half the oil would not be a good idea. A change of 10% is al I would do up or down. Remember that the fluid coupling has no stator. Therefore it will never work like a torque converter. There is never any torque multiplication. If ones fills it up to much, then there is no room for expansion when it gets hot and it will explode.

By changing the fill level, you shift the RPM when it locks to 1 to 1. You never change the torque curve just the RMP point when it does.

Tractor fluid does not, I am told, have the extra VI and Circulating additives. Also, I am told by Gyrol that they break down after about 5 to 7 years and that a coupling should have the fluid drained at that interval. The Mobile DTE can be had via Granger. It is a little pricy however. You pay for those additives.

James.

James, in your research, did you run across any recommendations regarding flushing the fluid drive before you fill with the Mobile DTE? I think my '42 Chrysler has automatic transmission fluid in it now. 

Not much in a Fluid Drive Coupling...just two grape fruit halves and bellows/and graphite ring seal up to middle of 1950.

Some pics...