Fluid Drive fluid, what is available in today's oils?

[Bruce48D24]

I tried searching for this information on this site, but did not get any result.  What are people using for the fluid drive fluid now?

If anyone knows the oil type and some vendors for it, I appreciate any info.

Thanks,

Bruce48D24

 

[Merle Coggins]

I used AW32 Tractor Hydraulic fluid from Farm and Fleet. I believe that's about as close as you're going to get.

[DonaldSmith]

Don't change the fluid drive fluid as a maintenance item.  Not like motor oil and coolant.   Maybe check the level, but there is a trick for that.  There was a recent thread on that.  Good luck finding it. 

 

(Two posts, May 16,2018)  

Edited June 19, 2018 by DonaldSmith

[James_Douglas]

 

 

*************************************** Fluid Drive Fluid Tech Note *************************

 

Technical Note on MOPAR Fluid Couplings

 (Fluid Torque Couplings are NOT covered by this Technical Note. Copy/Publish at will so long as you copy the entire 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 FluidCouplings.  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 fluidcouplings 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 drivefluid. 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.

 

As a post scrip in 2014.  I ran across and old Gyrol book that talks about the filling of the fluid couplings.  In short, how much you fill it affects the torque-stall curve.  Chrysler set that by the position of the hole in the bell housing.  However, if one is to fill it a little less or a little more one can change the curve.  Do so at you own risk and never fill it past 90% so it has air in it to compress less you blow the thing up!.

 

James Douglas

San Francisco

[Andydodge]

James..........I've never had nor driven a Fluid Drive mopar nor do I expect to in the future, they were available here in some Oz Dodges and DeSotos ,tho' am not sure whether any Oz Plymouths ever had this setup...........I enjoyed reading the report and commend you for taking the time to research this and whilst its not something or information I expect to personally need its good to learn something new each day.........thanks..... Andy Douglas.

[chrysler1941]

All the threads about fluid drive only talks about what goes in the coupling. Never about the transmission itself. 

Mine says 10W.  Using 10W at high speeds, mine pops out of 4th and will only return when letting of accelerator.

Replaced the 10W with the same ISO32, and presto, works like a dream for 2 years now.

[51_Meadowbrook]

I was told in a forum I have on another site that 10w oil was only a temporary fix. I drained mine in my 51 Meadowbrook and found the original fluid. It was suggested I replace it because of a stumble I had. I used ISO 32.  It didn’t work for the stumble but the rpms don’t drop way down when stopping in gear anymore. I also replaced the transmission fluid at the same time. The first picture is how it started coming out. The second is how the last quart or so came out. 

Edited June 22, 2018 by 51_Meadowbrook

[Dodgeb4ya]

That's the 3 speed transmission oil... looks ugly for sure.

The fluid coupling oil is checked via an access plate and hole in the floor tunnel.

Lot's of posts on how to check it.

[51_Meadowbrook]

Sorry, you are correct. I just figured it was worth pointing out that they do go hand in hand when replacing. 

Edited June 22, 2018 by 51_Meadowbrook