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mnskaggs46

1941 DeSoto fluid drive problems

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I have a 1941 DeSoto S8 Deluxe. I am having problems with the fluid drive transmission. When in gear it will not move, engine revives up. Sounds like something is slipping. Changed the fluid levels. When not on the ground wheels turn no problem but when under a load it will not move, engine revives up. Could it be the clutch? Need help on this one.

Fluids levels are fine.

Failed to mention that the fliud drive has a vacuumatic shifter on it. After discussing this people who have pre-WWII MOPAR vehicles, they think it is either the clutch or the transmission shaft going into the clutch.

Anyone have any more ideas before I pull the transmission?

Edited by mnskaggs46
Found new information. (see edit history)

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Check the fluid coupling oil level after making sure the clutch works OK. Read your'e shop manual for correct procedures.

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I second the motion to check the Fluid Drive unit. For complete information do a search for Fluid Drive in the Chrysler and Dodge sections. This subject has been covered exhaustively many, many times. There are a couple of long threads from 2008 with everything you will need to know.

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Check the fluid coupling oil level after making sure the clutch works OK. Read your'e shop manual for correct procedures.

Thanks done that on fluid level. Clutch seems to work ok. Clutch disk looks good but how do I check it out without pulling the transmission?

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Thanks done that on fluid level. Clutch seems to work ok. Clutch disk looks good but how do I check it out without pulling the transmission? I will check the links.

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In one of the threads that Rusty refers to there are trouble shooting tips and I recall it outlines checks to determine whether your problem is low fluid level in the fluid coupling or worn clutch disc and how to check the clutch adjustment.

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In one of the threads that Rusty refers to there are trouble shooting tips and I recall it outlines checks to determine whether your problem is low fluid level in the fluid coupling or worn clutch disc and how to check the clutch adjustment.

Thanks Bob, I really think it is a slipping clutch (adjustment is correct) or as a friend of mine said I may have damaged the input shaft to the clutch. In any case I will have to take out the transmission and have a look see.

Thanks again. Mel

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Just to be sure were all on same page,,,

There are 2 fluid leavels,,the fluid coupling on the flywheel;;

AND the transmission [the gearbox ]],,,

Lubrication systems totally separate,,I think,,,

Cheers,,Ben

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Ben got it, change fluid in both with 10w ND oil. Put the correct amount in both. Anyway going to pull the trans to see what is really up.

Thanks again,

Mel

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Ben got it, change fluid in both with 10w ND oil. Put the correct amount in both. Anyway going to pull the trans to see what is really up.

Thanks again,

Mel

Mel, PLEASE let us know the outcome.

Ben

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Ben got the trans out and it looks good not problems. The problem seems to be in the coupler (torque convertor). Clutch pressure plate and clutch disc spins freely which attached to the coupler. With them off the driving disc plate spins free and is wobly. So I have made a decision to replace the whole coupler assembly this should fix the problem. I will let you know how it goes.

Mel

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Once again... Chrysler Corp did not make a car with a torque converter until 1951. Your'e car has a very basic fluid coupling unit. Finding a good used one for a 1941 or 1942 Mopar car might be tough if you really do need one.

Edited by c49er (see edit history)

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The fluid coupling is a pretty simple device and has little that can fail mechanically. If you had the correct oil level in the coupling and it is not leaking, driven side turns freely, then I would suspect the clutch pressure plate and friction disc. That is the friction lining on the disc is worn down to a point the pressure plate is not squeezing it tight enough to overcome the inertia to move the car, or, the springs in the pressure plate are weak and/or the surfaces of the pressure plate and the driven disc are warped and therefore don't have sufficient contact with the friction disc.

Someone else may have a different and better opinion. Back in the 60's I had a 50 DeSoto that had the same symptom but it was low oil in the coupling. I recently got a 52 Imperial that has the Torque Drive, same M6 trans your car but with a actual torque converter. I haven't driven it much but it does have better acceleration from a dead stop than the fluid drive.

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Mel, Everyone including me, is leaning toward the fluid level in the Fluid drive unit. You say you changed the fluid and added the "correct" amount. When you access the service plug through the floor board, the service plug is about 5 - 10 degrees from top dead center. This is intentional to prevent overfilling of the unit. I've been told to fill the unit until it won't hold any more oil, at the slightly tipped angle. It ends up about 90% full. Over filling will also affect the stiring action. But filling is not a measured amount. So when you say you have the correct amount of oil, is that a measured amount, or a visual amount? Ron

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Bob, I am getting the fluid drive assembly checked out because I think it leaking why would it stop pulling while driving down the highway. Order rebuilt pressure plate and clutch disk since I have it apart thought I would change them out. Thanks, Mel

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Ron, you are correct. The book calls for 2 3/4 pints of 10w ND oil for the unit. Now everyone is tells me like you to fill it up. Getting the unit checked out because it was leaking. No visible evidence of that but car stop moving while going down the highway. Engine would revive up but would not go. I have another unit coming which is not leaking (used). Before putting it in we will top it off as you have indicated. Thanks, Mel

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In my working days as a mechanic at a large transport company I had to repair a couple of old lift trucks with straight inline dodge 6 cylinder engines . That is the one with a long INTAKE manifold. The problem was if the driver did not get it started first time, the system got flooded . I had to change the spark plugs ,or nothing doing. It also had a fluid coupling between the flywheel and clutch. At one time I had to send out a fluid coupling for repair. They put it on a lathe and cut it open. Inside were lots of broken pieces. It was repaired ,put back in position on the lathe and wire welded. I was told to fill the assembly with Delco A T F ,HOLDING THE FILLER HOLE AT TEN TO THREE position. It worked fine after. A driver told me when he was a teen ager pumping gas, a driver with a Hudson came in. Slipping clutch and wanted to sell the car. The jockey offered him fifty dollars. Sold. Mr. jockey drained the wet clutch oil ,flushed the system with some sort of tetrochloride, and put in the correct fluid . Problem solved. You see those clutch discs were lined with cork. Wine cork. I fixed a few in my days. Some of the old Baker forklifts and old Triumph motor cycles had them . Those clutch housings are sealed with gaskets. and the starters drive gears also have special rubber seals.

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Mel

The 2 and 3/4 pints is for the transmission case. The fluid coupling holds a lot more than that. The manual for my 52 Chrysler says the coupling is 13 inch diameter and takes 10 1/2 quarts of 10W oil. ALL CHRYSLER MANUALS FOR CARS PRIOR TO THE TORQUE FLITE AUTOMATIC SPECIFY 10W MOTOR OIL ONLY FOR TRANSMISSIONS, FLUID COUPLINGS AND POWER STEERING.

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Mel, 2 3/4 pints sounds awfully low. I don't have my shop manual with me but that sounds more like the transmission gearbox. Normally the fluid drive needed no service so there was no capacities listed as I recall. Those things are about 18" in diameter and 4" thick. They are not hollow but I think they hold closer to 3 -4 quarts. (It's been over 10 years since I redid mine) Maybe I'm wrong. As far as Trini's comment, there are two seals involved with these fluid drive units. One kind of resembles an accordion or paper wrapped spring and acts as a shock absorber. The second seal is a graphite ring (about 3" dia) that provides the slip surface. This ring is a fragile piece. When mine shattered there were pieces inside the unit. But it leaked like crazy once that broke. As I recall I sent it off for repair to Northwest transmissions in Winchester, Ohio. They had the seals too. As a note, once you fill it more than half full, if the seals are bad, it will start dripping. ( see Bob was a little quicker to respond than me) Ron

Edited by Ron42Dodge (see edit history)

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This one forklift was prewar made by Hyster and used a dodge engine with an updraft carburetor. It had a forward and reverse lever and a clutch pedal tool. I am sure I was instructed to fill the unit with G M A T F at a ten to two position. trini

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My shop manual says the fluid of the fluid drive unit should be maintained at the level of the filler hole. The Motors manual says to fill it until it runs out. Neither state a capacity of the unit. Suposedly they can be air tested no more than 15 lbs if you had a fitting that would seat in the service hole. They also said they can be tested like an inner tube in water. I still believe you just need more oil.

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Hi Ron, I think you are pretty close. How about draining the unit completely. Then measure the amount of whatever oil your manufacturer says, fill right up, then hold the unit with the plug out at a 2 o'clock position and let the excess drain out . Do it in a clean receptacle so you can measure properly.. That way you will know for sure how much fluid it holds. Turn the input shaft a few times to remove any possible air. You can fabricate something by attaching an air line to it through an air adjustable guage at eighteen lbs, immerse it in water and look for bubbles. You may get a spare plug, drill a hole through it and solder or braze a piece of brake line in that end and solder or braze an air hose fitting at the other end. That way you will be able to connect your shop air hose. You may also try attaching a 5/16 flexible fuel hose at the brake line and with the pressure in your air tank at 18 lbs stick the air nozzle into the flex hose. This is only my humble suggestion.

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CORRECTION. THE AIR PRESSURE SHOULD BE NO MORE THAN 15 POUNDS. If the unit has a leak and is running in the car, it will spray oil out . How much will depend on the size of the hole and duration of use . trini

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Thanks to all who responded. Got another fluiddrive which does not leak. Sent old one off to check out. This week we will installing the fluiddrive, rebuilt clutch disc, pressure plate and new throw out bearing. I will give you all an update. Thanks again. Mel

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Here is an update. The Fluiddrive assembly I sent off to get rebuilt can't be rebuilt. Seems the main drive penion bearing front went bad. Trans shaft had to much play in it. Wobbled out the bearing and seats in the fluiddrive. I am replacing the bearing in the front of the trans and going to use the other fluiddrive assembly. While the trans is out replacing clutch disc/pressure plate, throw out bearing, etc. Hope this works. Thanks

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