Fluid drive service

[Doug&Deb]

So to service the fluid drive unit do I remove the clutch inspection cover then rotate the drain plug straight down? The service manual really doesn’t explain the procedure. After draining rotate the drain plug to the correct angle and refill to the top. Sound right? I’ve topped off the unit but after 7 years of ownership a refill with fresh fluid seems like a good idea.

[Worden18]

I might not be the only one who suggests this, but unless you have a major leak, IMO I'd leave it alone.  My Meadowbrook still has the original 70 year old oil in it...works perfect.  Before you go draining anything wait for some others to give opinions. 

[Dodgeb4ya]

I second the leave it alone.

Certainly a real pain in the arse

job to drain and fill one.

[Frank Elder]

IF IT IS NOT LEAKING RESIST THE URGE TO SERVICE THE FLUID DRIVE.........BY THE TIME YOU PASS AWAY IT WILL STILL BE WORKING JUST AS IT SHOULD IF YOU NEVER OPEN IT.

Fluid drive is the rough equivalent to Pandora's box, it should never be opened just to satisfy your urges. 

[James_Douglas]

I disagree based on my research.  Read the following and be advised. (This thread is in the system if one looked).

 

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

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

 

[Doug&Deb]

I’m inclined to agree. That explains why the service manual doesn’t cover a service process. I’ll just keep driving it till it goes boom.

[Dodgeb4ya]

I have never changed fluid in any of my fluid drive cars.

Two alone of which I have owned for over 40 years.

Don't want a leaker.

[Doug&Deb]

Just out of curiosity does anyone know what size magnetic socket for the fill plug on the fluid drive unit? I’d like to at least check if it needs topped off.

[Dodgeb4ya]

3/4" hex plug. 

[Doug&Deb]

Thanks 

[Doug&Deb]

Of course I’m still not sure how to drain and refill should I ever decide to. I’m going to at least do a slippage test and perhaps top off the unit. I’m inclined to agree with James Douglas about these units. He’s done more research than anyone I know. New fluid can’t be a bad thing. I do however know my mechanical limitations.

[Frank Elder]

14 minutes ago, Doug&Deb said:

Of course I’m still not sure how to drain and refill should I ever decide to. I’m going to at least do a slippage test and perhaps top off the unit. I’m inclined to agree with James Douglas about these units. He’s done more research than anyone I know. New fluid can’t be a bad thing. I do however know my mechanical limitations.

That of course is your decision to make, If I had a grandfather clock in the hallway that hadn't been moved for 75 years and it kept perfect time.........Should I take it apart just to make sure it kept good time for the next 25 years....? My cheesy analogy and my last effort, good luck and the best of results with your endeavor.?

[Plymouthy Adams]

apologies to Frank...was not my intent nitpick his analogy....most folks when they have a nice no leaking unit leave well enough alone...but as Frank says, this is your call completely....I know I would not mess with it if working.

Edited November 22, 2020 by Plymouthy Adams

[Frank Elder]

4 hours ago, Plymouthy Adams said:

Franks an old grouch!

Edited November 22, 2020 by Frank Elder

[Plymouthy Adams]

yo Frank.....here is a good one.....

[Tom Skinner]

First: Thank you James Douglas for very valuable information. I have owned 1948 Chrysler Royals with Fluid Drive for 47 years. Never touched the F.D. units. 

Second: Grandpa used to say "If it ain't broke then don't fix it.

Third: The new ISO 22-32's etc. may have detergents in them that might eat up a compromised/older slow leaking seal.

But hey, for those of you that can't leave it alone - have at it. Personally if I did drain one I would run it through a panty hose filter

several times and re-fill it using the same fluid, (Maybe have to add a touch of ISO 32 to complete the fill).

Es ist mir egal. It is all equal to me. Enjoy your choice.

Tom

[Frank Elder]

I wonder how many microns a panty hose filter is....lol. Pretty good idea though.

[Plymouthy Adams]

not sure Frank...they say a well dressed lady when passing gas balloons at the ankles....?

[James_Douglas]

2 hours ago, Tom Skinner said:

First: Thank you James Douglas for very valuable information. I have owned 1948 Chrysler Royals with Fluid Drive for 47 years. Never touched the F.D. units. 

Second: Grandpa used to say "If it ain't broke then don't fix it.

Third: The new ISO 22-32's etc. may have detergents in them that might eat up a compromised/older slow leaking seal.

But hey, for those of you that can't leave it alone - have at it. Personally if I did drain one I would run it through a panty hose filter

several times and re-fill it using the same fluid, (Maybe have to add a touch of ISO 32 to complete the fill).

Es ist mir egal. It is all equal to me. Enjoy your choice.

Tom

Tom,

 

All ISO fluid is not the same. When I had the MOPAR factory fluid analyzed, it had two additives. One was a rust inhibitor and the second was an anti-foaming agent.

 

When I talked with the Engineer at Gyrol, who licensed the technology to Chrysler and still makes industrial fluid couplings, he said the same thing.

 

If you read my write up on fluids you would have noted that I SPECIFICALLY stated that one should use Mobile DTE Light Circulating Fluid 32. The full specification is below:

 

Grade                                                                                        ISO 32
Air Release Time,                                                                     50 C, min, ASTM D3427    3
Copper Strip Corrosion,                                                           3 h, 100 C, Rating, ASTM D130    1B
Density @ 15 C,                                                                         kg/l, ASTM D4052    0.85
Emulsion, Time to 3 mL Emulsion,                                           54 C, min, ASTM D1401    15
Flash Point,                                                                                Cleveland Open Cup, °C, ASTM D92    218
Foam, Sequence I,                                                                     Stability, ml, ASTM D892    0
Foam, Sequence I,                                                                     Tendency, ml, ASTM D892    20
Kinematic Viscosity @ 100 C,                                                    mm2/s, ASTM D445    5.5
Kinematic Viscosity @ 40 C,                                                      mm2/s, ASTM D445    31
Pour Point, °C,                                                                             ASTM D97    -18
Rust Characteristics,                                                                   Procedure A, ASTM D665    PASS
Rust Characteristics,                                                                   Procedure B, ASTM D665    PASS
Turbine Oil Stability Test,                                                             Life to 2.0 mg KOH/g, h, ASTM D943    5000
Viscosity Index,                                                                            ASTM D2270    102

 

Make note of the Copper Strip Corrosion rating. At the end, notice the "1B" what this says is that this oil has the lowest rating on the ASTM copper stip test meaning it will not harm any copper or brass parts. Also, there is no detergent in this oil as there is in motor oil and ATF.

 

The only other part that is not steel is the graphite seal and I doubt that the oil would bother with that. But to be sure, I have email American Graphite who made and still makes seals asking them.

 

James.