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Changing fluid on fluid drive unit


jharring10

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I have a 1949 Desoto S11 second series that I have owned for 40 + years and has run flawlessly until Ethanol gas additive was introduced in the auto industry. In 2008 the car started to hesitating on the highway like it was starving for fuel but it would never stall.  The problem eventually got worse and has been un drivable for the past few years. Various people made recommendations as to what the issue could be. Sludge in the gas tank was a suspect as Ethanol may have loosened years of dirt going back to the days of leaded gas. It seemed to run a little better when it sat for a while (dirt settled) and worse when I filled up the tank and mixed up the sediment. Last summer I decided to replace the gas tank and now then car would not start. Tried priming the car and it would start until the gas burned out or the carb. I finally decided to take the same approach that Ii did when I had issues with the brakes leaking brake fluid.  Rebuild the entire fuel system. So that’s exactly what I did last fall. New gas tank w gas gauge sensor, rebuilt carb and when I removed the rubber fuel line I found the issue as there wasn’t much left of the line and was sure sucking air. Replaced the line and the sucker fired right up! Little did I know that the fuel pump was leaking like a sieve.  Ethanol apparently destroyed the seals. Bought a 6 Volt electric fuel pump with an attached fuel filter and problem solved. She now starts and runs as good as ever but now a new problem and that is Fluid Drive. Sorry for the long story but I want to provide as much history as possible.  When I took the car out for a test drive, she backed out of the garage in reverse no problem. I then put her in high gear (shifter down) and she took off but will not shift into the second gear. I have been taking her in the neighborhood for the past couple of weeks trying to loosen it up but no luck.  Semi-Automatic  transmission issues have been my biggest fear with this car and now it has happened. I have never done anything to this tranny. When I spoke with some of the older mechanics about fluid drive, their response was “if it isn't broke don’t fix it”.  It was recommended that I start with changing the fluids on both the tranny and fluid drive unit. I recently drained the tranny and added fresh 10w oil. I have also purchased hydraulic ISO 32 "tractor hydraulic fluid" for the fluid drive unit but have no clue as how to drain and replace the fluid. Any recommendations would be greatly appreciated.

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J. Harring,

Check and Clean the Governor's points on the Tranny.

Also check to see if the RPM's are below 500rpm's at Idle. The tranny will not upshift if Idling too high.

There is a special section in your Service Manual on just this problem with a checklist to pin it down.

If pump doesn't reach 30-40psi in tranny it won't upshift.

Try checking the fuse on your tranny relay switch, is it good? Not burnt?

All ground connections as well.

Look - in plain speak - this is a mechanic's car - not real reliable - until you become a reliable mechanic.

(By the way if you open your Fluid Drive Unit Fill Bolt and it's full - do not mess with it - close it back up and proceed to your manual - see above)

Good Luck!

I too have owned several 1948 Chrysler Royals with Fluid Drive - a lifetime of research - fun - and work.

Happy Easter.

Tom

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To locate the fluid drive fill plug you will need to get under the floor mat on the transmission hump on the passengers side. There should be a small cover there somewhat like the cover over the master cylinder.

 

Removing that cover will allow you access to the plug/cover in the bell housing.

 

Removing the plug/cover in the bell housing will reveal the fluid coupling.

 

Fluid coupling must be rotated until it reveals the threaded plug.

 

To drain it the plug must be removed.

 

Either use a siphon to get the fluid out, of rotate and let it drain (read as spill) out the bottom.

 

After drained rotate the fluid coupling until the hole in the coupling again aligns with the access hole in the bell housing.

 

Fill per your manual until fluid is at the level of the plug.

 

Edit: spelling

 

EDIT 2: let me add that this is not an endorsement to change the fluid. Just the "how to" as an answer to the OP ?

Edited by shel_ny
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check the electrical connections from the carb to the transmission. as stated previously, fluid drive is simply a hydraulic clutch, has nothing to do with tranny function. you said you had carb rebuilt, make sure shift solenoid connections are correct. 

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Well, I just registered and signed in in order to assist with the initial question. I see it has been thoroughly answered, so I'll not go there. Just to add this, the transmission is the M-6 which is used behind either fluid drive couplings or torque converter as in a V8 engined car such as a 51 - 53 Chrysler or Imperial.

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I agree with advice offered above, if the fluid coupling is up to the correct level, leave it alone, it has nothing to do with the shifting.

 

The transmission shifts range with hydraulic pressure which is proportional to speed.  It will work without the electrical controls but will not downshift since the downshift is effected while in motion by dumping the hydraulic pressure.  It could be, due to a fault in the electrics that the trans is in "downshift Mode"all the time.  Disconnect the electrics and drive the car to see if you get an upshift.  If you do, then you must find the fault in the electrical circuit and the first place I would look is at the carburetor kick down switch.( which completes a ground when pushed in )  Possibly someone has reversed the wires that go to the switch and to the coil above the carb bowl ,(which is there to enrich the mixture) .

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Guess we have to keep hammering at this.  You do not have a fluid drive transmission.  You have a hydraulic power transfer unit between the engine and the M6 semiautomatic transmission.  Like all soap is ivory, all tissue Kleenex and all window cleaner Windex.  All fluids drives are confused with the transmissions behind them.   This is not a dig against any one, just a reminder that the components are seperate and have separate functions. Not to mention different and specific lubricants.  

 

Check the Imperial Club website in their repair section for a primer on all thsoe things mentioned above.

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Don't mess at all with the fluid drive coupling other than to check the fluid level.

Up Shifting problems are either idle speed, wiring, solenoid, governer or transmission fluid lever or many other possible issues. 

Get a factory shop manual and read it and use it to fully understand how to repair and fix problems with your car.

The factory service manual will have the right answers as will the Master Technicians Service booklets ....... Vol.2 No.11   Vol.2 No.12 and Vol. 4 No. 

 

If the car was sitting for several years I would check just the transmission  (M-6) fluid level as they seem to leak a little. . The fill plug is on the right side in the middle. It needs to be full so the oil pump can build up 40PSI or more oil pressure to cause an upshift.

Fill the trans till oil runs out of the fill plug hole.

Top it off with 10 Weight oil. Others use tractor fluid... I don't.

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Good advice on checking the two wires to the carburetor, to make sure they run to the right places. Maybe this belongs to the "stupid is as stupid does" thread, but on my car I had the two wires switched, and things didn't seem to work right.  A major "Duhhhh!"

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I had ongoing issue with my 48 Chrysler with fluid drive(says so on the brake light cover) or if others prefer, "fluid coupling". Search my posts. There is a great reply that has an old training film in it. Watch it and you will be able to solve the shifting issue. Mine boiled down to the wires from the relay and the button in the governor. Fixed the first with new wires and the car ran great for a bit then would not shift again. Then fixed the governor. No issues since. "Remember up is up and down."

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Thanks for the great advise everyone. First I want to reply to shel_ny. My DeSoto is a 49 first series (looks like 48). I mistakenly identified it as a second series in my original post so I believe this does make it an S-11. To everyone else. I already did clean the points on the tranny. I also decreased the idle on the carb to see if that made a difference which it did not. Before it sat for a while it was a little sluggish shifting for a few minutes until she warmed up. Another mechanic suggested that I change the tranny fluid with fresh 10w and clean the filter screen which I recently did (the screen was filthy). I have not driven the car since I did that. Sounds like I should leave the fluid drive alone. It may be possible that I reversed the connections on the carb when I reinstalled it after the rebuild. Sounds like I should go through all electrical connections as a next step.

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I was hoping that I was onto something with the connections to the carb maybe being reversed. However, that is not possible as one connection is a ground to the carb and the other plugs in so they cannot be connected in reverse. I will be taking her off the jack stands and fire her up for a ride and start to go through every electrical connection. Is it possible that something in the carb changed when it was rebuilt? She starts and runs as good as ever though.

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Disconnect the wire to the transmission solenoid and if it doesn't upshift there is an issue in the trans. The solenoid only gets power to hold the transmission in 1st or 3rd. If the solenoid has power all the time the trans won't upshift in either range.

Does it shift up to 2nd in low range?

Earl

Edited by mopar_earl
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  • 1 month later...

So I got back to addressing my shifting issue last weekend. There are three connections on the tranny and I disconnected the one to the solenoid which by the way I pulled apart and cleaned the contacts as recommended in another forum. I took her for a ride and she was in fact now in the higher gear. I then decided to go for a little a cruise on a main road as she may be a little slow taking off but I can now run at an acceptable cruising speed. I got a little way up the road and she stalled and I could not get her started. I reconnected transmission solenoid  and she started right up but ran in the lower gear. Disconnected again and same results. Not sure what correlation the transmission solenoid has to do with providing fuel to the carburetor.  Also, one thing I failed to mention is that I converted the stock fuel pump to a 6v electric as Ethanol destroyed the seals on the stock one. Any help would be greatly appreciated. At a stand still right now.

Edited by jharring10@live.com
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  • 4 months later...

The GyroMatic in my 50 Coronet will not upshift unless the clutch pedal is depressed. But what is the technical explanation for this? Another question: what is the correct filler cap for the trans, the upper one in the side or the one top next to the solenoid? And yes, I know it needs nearly 3 pints, but the question is if I do any harm by pouring the 3 pints in the top hole (far easier than using the one on the side...)

Edited by HotRodHerman
precising question
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My 50 dodge didn't start. Unhooked the wire from coil to the, can't think what it's called not, on the aircleaner bracket where wires go to carb and trans. Now starts better than it ever did. If I come eo complete stop it will shift down, take off and let up on gas and it shifts up. The only thing it doesn't do is if I slow down and floor it no down shift.

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10 hours ago, HotRodHerman said:

The GyroMatic in my 50 Coronet will not upshift unless the clutch pedal is depressed. But what is the technical explanation for this? Another question: what is the correct filler cap for the trans, the upper one in the side or the one top next to the solenoid? And yes, I know it needs nearly 3 pints, but the question is if I do any harm by pouring the 3 pints in the top hole (far easier than using the one on the side...)

Fill it through the side with a small hand fluid pump or a flex funnel through the floor access opening......M-5 is shown but fill and drain plugs are the same.

 

M-5 Drain and Fill.JPG

Edited by Dodgeb4ya
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