View topic - 1950 desoto transmission not shifting

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PostPosted: Tue Jul 13, 2010 10:21 pm 
I have a 1950 desoto custom with the fluid drive and it will not shift automaticly when i take my foot off the gas. Any ideas?


 Post subject: Idea #1..........
PostPosted: Tue Jul 13, 2010 10:28 pm 
..........idle speed set too high.

Check that and report back

PostPosted: Tue Jul 13, 2010 11:10 pm 
I agree with Steve. It is the first thing to check. The rpm's have to drop to about 500 or it won't shift.

 Post subject:
PostPosted: Thu Jul 15, 2010 3:50 pm 
Next step, if you are mechanically inclined to do so, is to take out the transmission.

Use your shop manual, and separate the front from the back. There is a screen between the the halves, that tends to clog with years of gunk. That prevents the flow of oil, to allow the shift.

It is not as simple as it sounds, to separate the halves. It is a long, process, but if you follow, step, by step, it will get you there. I have done 2 of them. The screens were plugged in both of them.

My '52 was traveling down the Interstate, when the oil pressure dropped(due to lack of fluid, because of clogged screen) and caused the shift back to low. WOW...............

That prompted me to find out what happened. I learned a lot about how very simple, but, at the same time, how advanced these transmissions are.

Good Luck.

Mark Waite

 Post subject: transmission problems
PostPosted: Thu Jul 15, 2010 8:29 pm 
I'm going through a repair process on a 49 Chrysler with fluid drive. The shop manual calls for 450-475 rpm idle speed on a warm engine. It's also a good idea to trace the wiring system for the fluid drive from the transmission to the engine area and make sure all connections are secure. If by chance the pushbutton on the carburetor is stuck in the depressed position, this will prevent upshifting. Also check the fluid level in the transmission-too low will also mean no upshift.
Marty Lum

PostPosted: Thu Jul 15, 2010 10:10 pm 
I have to disagree with my friend Mark on this one. The service manual has electrical and hydraulic checks that should be performed after the carb is set to the correct idle speed and a visible check of the wiring to make sure everything is connected. Also, make sure a wire is not shorted to ground somewhere. One of the things I learned in my conversation with John at Northwest Transmissions was that on earlier Fluid drives that filter screen was accessable from outside the transmission. I don't remember what year they put that screen inside so you have to take the transmission apart to clean it but I am thinking on the 1950 it might still be accessable from outside. I would consult the service manual and do the checks and everything else possible before taking the transmission apart.

PostPosted: Thu Jul 15, 2010 11:45 pm 
I have 50 custom with fluid drive (haven't been driven in the past 7 years though) and, if remember correctly, user manual says that to up-shift you have to accelerate to approximately 13 mph and then let it slow down to about 8 mph (and it's supposed to downshift when you stop the car). Worked for me most of the time when I followed this instruction. The problem here - all these impatient drivers behind you... I believe there was an aftermarket solution marketed as "Easy-Shift" knob. It's a knob with a push button mounted in place of a standard gearshift lever knob with a single wire running to the solenoid relay. It suppose to allow you to up-shift "at will", overriding governor rotating weights switch. So if everything else is in good shape (wiring, governor, solenoid, solenoid relay, etc.,) - that may be a good solution.

- Igor.

PostPosted: Fri Jul 16, 2010 4:07 pm 
Igor-I just purchased one of these aftermarket pushbutton setups for a 49 Chrysler I'm working on. The push button is to do a downshift from 4th to 3rd without needing to floorboard the gas pedal.
My project car would not downshift by flooring the pedal due to poor functioning of the pushbutton on the carburetor. I actually rigged up a wire from the carb connection to the cockpit and used a remote starter button to test the system. It downshifted just fine via the pushbutton so I'm going to installs the pushbutton kit on the end of the shift lever.
Marty Lum

 Post subject: Trans not shifting
PostPosted: Tue Jul 20, 2010 3:50 pm 
Ok I adjusted the idle down and that didn't work, I am now going to trace the wiring to see if it is hooked up correctly and try to locate that screen in the manual.

Thanks to everyone I really apprieciate the help.

PostPosted: Tue Aug 10, 2010 8:09 pm 
Ok I traced all the wire and they are correct. The one thing I noticed in the shop manual was a wire going from the anti-stall control on the carburetor to the kickdown switch on the carb.

I do not have this wire and I am not sure where this wire would plug into on the kick down switch.

Would this cause it not to shift into those two gears?

PostPosted: Tue Aug 17, 2010 5:36 pm 

Joined: Wed Aug 11, 2010 6:23 pm
Posts: 9
Hi-I've been driving the bugs out of a 49 Chrysler for the last 6 months. It too has fluid drive. It would upshift fairly promptly after I reset the idle to 475 rpm but it would not downshift on the road by flooring the throttle. When you turn into a side street at lower speeds, this is a problem as 4th gear doesn't have much lugging power at 15-20 mph. The hardware on the carburetor includes a pushbutton assembly on the rear part of the carb plus an electromagnet on the top of the carb. The pushbutton is actuated by the carb's throttle linkage and will downshift when you floor the throttle at speeds between 20 and 40 mph. Neither of these 2 carb items has any direct effect on upshifting (normally) if the pushbutton is stuck in the depressed position due to a broken spring, it will prevent upshifting as the unit will always be grounding the circuit. You might want to remove the carb and then remove the 4 screws which hold the pushbuttom parts on the carb body to see if anything is broken.
The wiring harness from the transmission should come up to the engine compartment and attach to the coil, a relay and voltage reducer box on the LH inner fender, and the 3 leads on the carburetor. If these leads are disconnected, it suggests someone once thought the pushbutton on the carb was a problem.
The kickdown switch should have a small tang with screw on the inboard side of the carb. You loosen the screw and attach the wire. The other 2 carb wires connect via male plugins to the top of the carb at the electromagnet.
If these leads are not attached, you will not be able to downshift.
I was finally able to get my project to downshift on the road by rebuilding the carburetor and putting a lighter duty spring in the pushbutton mechanism. If the throttle linkage is not properly adjusted, this too will prevent the pushbuttom assembly from working.
The shop manual diagrams and printed instructions are quite helpful.

My transmission wiring harness was a mess and disconnected at the carb when I started working with this car. Contact me at for wiring harness sourcing if you feel the need.

The troubleshooting in the shop manual suggests most shifting problems are due to electrical problems or low hydraulic fluid level.

Shifting is slow under the best of circumstances but it is handy in traffic to just leave it in high and not need to punch the clutch.

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