Fluid Drive Stalling

[James_Douglas]

Hello, I would recommend that you sit down and read a copy of my post of many years ago.  The fluid couplings work by the velocity of the fluid pushing the internal fins.  They do not work passed on any pressure or on the viscosity of the oil.  Also, if you do not have a dashpot in working order the car will stall often when coming off of a stop sign.  In addition to all of that, I ran across a Chrysler tech note that said that a fluid coupling should not be left engaged for longer than 5 minutes at idle.  So, if you are stuck in a traffic jam, put it in neutral until the traffic starts to move.

 

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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 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.

 

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

  

[Nighshade]

Great, but all i can find is 5 gallon buckets lol. 

[51_Meadowbrook]

James, thanks for the detailed information. It’s very helpful. I ran my Meadowbrook around for about an hour and a half and it stumbled and did everything I mentioned before. Then about an hour into the ride it stopped dragging at the stops and didn’t stumbled when I took off. I assumed that the fluid finally worked through and everything was great. The next day I took it for a short 15 minute ride and it acted up like before the whole time. Today I took it out for about an hour and it did the same as the longer drive I mentioned, for the first half of the ride it acted up then it started running beautifully. Is this just one of the finicky cars that is angry until the transmission heats up enough and then it runs great? Its such a pleasure to drive when it runs without problem. 

[busycoupe]

You never mentioned if this car was just taken out of long term storage.  Is it possible that you have bad gas in the tank? That could explain the erratic operation you describe.

[51_Meadowbrook]

It was away for the winter but the stumble and low idle has been an issue since I got the car 5 years ago. It leads me to believe that the dashpot plays a bigger role than people are making it seem in terms of keeping the rpms up. Also it has a fresh tank of gas and ive gone through half a tank already. 

[51_Meadowbrook]

 

[Tom Skinner]

Sharps40,

Ditto.

Check Points, Condenser, Cap, and Rotor. Set Timing with a Vacumn Gauge. Look for 20 inches steady hand.

Get RPM's to just click at Upshifts - say at 550 RPM. Drive it every day until it runs smooth.

A Car that sits - especially a Chrysler Product must be run. Do not let it sit for long periods.

Put non-ethanol gas in it. Use QT Gas if possible. Crap Gas will always screw things up (ethanol gas)

Drive it.

Tom

[51Traveler]

I need help I have a 1951 Chrysler wichrysler Windsor and someone put in an aftermarket 12 voltwelve Volt fuse Box and wiring harness it's an wiring harness that just cut the wires to all the transmission components components and I need to figure out how to how to wire the transmission so thit's commission so that it will idle at a stop with the clutch out . I'm looking online it doesn't seem that I have the little square box that has 4 wires coming out of it that is connected to the coil I do have the interrupter switch on the transmission the governor and it looks like there is a cell annoyed then up on the carburetor I've only been able to find two electrical connections clear up on top of the carburetor there's nothing down on the side that would indicate the downshifting control module I guess so now coming off the transmission all I have is a green wire a red wire and a yellow wire and I have no clue where they go. Or if I'm missing any other components