1949 Desoto tip toe shift conversion to standard?

[Desoto Joe]

Help! I am having problems with my tip toe shift, semi automatic, M-6 transmission slipping out of 4th speed in my Desoto S11. It has fluid drive. I don't really want to get away from the original, but I am curious to know if it could easily be converted to use a standard 3 speed Chrysler/Dodge/Plymouth trans in place of the semi automatic?

[junkyardjeff]

I heard plymouth parts will work but the crossmember the bellhousing bolts to will need to be moved,if you could find a parts car with the regular 3 speed it would be much easier but good luck in fiding one as I only seen a couple. I have a good used fluid drive trans from a 50 chrysler in the shed that I will probably never use that I will sell cheap

[Rusty_OToole]

It would be easier to fix the tip toe shift. What do you mean slipping out of 4th?

If you mean what I think you mean it could be the trans is low on oil. There is a little pump in there that pressurises the shifter, if oil is low, no pressure, and it won't stay in 4th.

Could even be something as simple as a loose wire. Or a short, the wires get frayed and the insulation falls off after 40 or 50 years.

[Rusty_OToole]

It is possible to change to a straight manual trans. I know a mechanic who changed one in a day back in the fifties. When the customer came to pick up the car he drove straight into a wall, he was not used to the car taking off as he released the clutch LOL.

[Desoto Joe]

Dear Rusty and others, thanks for responding, I have put in new fluid and the level is good. It helps some. I was also thinking that maybe some of the valves inside the trans were sticking so I did lubricate thru the interrupter switch hole with about 2 oz of Marvel Mystery.

When I say it slips out of 4th. . .I mean it slips out of the highest gear and goes to neutral. . .you can let off the gas and it will go back into gear. . .for a while. . .now this only happens sometimes.

This past Wed. I drove it about 15 miles, the 1st 5 miles it slipped out occassionally the last 10 it didn't. I also noticed a bad vibration sometimes. . . anyway my rear u joint busted that same day and my mechanic told me it was binding up. . .of course I have to replace these U joints. . .but do you think the binding up U joint could have been causing by trans to slip out of gear? Thanks, Desoto Joe.

[De Soto Frank]

When I say it slips out of 4th. . .I mean it slips out of the highest gear and goes to neutral. . .you can let off the gas and it will go back into gear. . .for a while. . .now this only happens sometimes.

do you think the binding up U joint could have been causing by trans to slip out of gear? Thanks, Desoto Joe.

Yes!

If a u-joint were binding-up, and causing the driveshaft to whip up & down / side to side, that could definitely cause the tranny to jump out of gear.

When it "slips out of gear", does the column shift lever move ? ( literally "jumping out of gear" )

You could also have an electrical fault causing the kick-down circuit to become energized, which will energize the solenoid, causing it to divert internal oil pressure of the transmission, and the car shifts down into the lower speed of the driving range that you're in. It'll feel like "neutral', because the lower speed of each driving range ("1st" and "3rd" ) are "free-wheeling", and there is no compression braking from the engine.

I had problems with my '48 New Yorker with a crumbling wiring harness to the transmission, allowing the wire from the tranny to the kick-down switch on the carb to ground-out intermittently, causing the tranny to suddenly downshift on its own, or to not upshift.

Suggest you get a reprint of the factory shop manual and/ or find a MoToR's or Chilton's hard-bound manual that covers your car, and read-up on the operation M-6 semi-auto.
IT IS DIFFERENT THAN ANTYHING USED SINCE 1955 !!!!

For inline help, if you visit the website "the Imperialist" ( Chrysler Imperials), they have very good scans of original service bulletins available for download, and the semi-auto is covered in detail.

I think it would be more trouble to swap to a different tranny than to make yours work right.

You would have to find a 3-speed manual trans from a MoPar equipped with Fluid Drive, as the input shaft is longer than for non-FD cars. The greatest number of these still around would be '46-'48 Dodge.

Get some service literature on the M-6, and follow the diagnostic processes, replacing any faulty wiring before you embark on a tranny swap.

Once I got the tranny in my NYer sorted out, it performed reliably for another 40,000 miles, until I retired the car ( early 1990's).

[Desoto Joe]

Thanks Frank, for all the info and time. After I replace the U joints I'll check all the wiring.

[Desoto Joe]

And Frank, to answer your question, it does not go out of gear on the column shifter. . .it happens in the trans

[martylum]

Hi Joe-I have a 49 Chrysler in the shop with fluid drive and have worked to improve the operation of this car's trans. for several month. The 49 Chrysler or Desoto shop manuals gives a very clear explanation of the inner working both mechanically and electrically.
It sounds like your car's hydraulic pump in the transmission body is failing to maintain a steady flow of hydraulic pressure to the shifter fork which keeps the transmission in the higher or 4th gear. This could be caused by a low oil level, improper fluid, or an electrical malfunction. Using the troubleshooting procedure in the shop manual will point out the problem area.
One simple on the road test is to see if it will shift from 1st to 2nd gear in the low range position at 8-10 mph. If this won't occur, then you'll certainly have problems keeping it in 4th gear.
A test drive in my car yesterday found everything working well except the ability to downshift to 3rd gear on a hill by flooring the accelerator. Flooring produces no downshift.
I think the transmission is well worth fixing up as the transmission is pretty convenient in city driving and some online searches suggest they were relatively trouble free transmissions..
Martin Lum

[Desoto Joe]

Thanks Martin, What fluid/oil are you using in the M-6 trans?
The book calls for 10w motor oil which is hard to find. I am currently using a NAPA product 85-401 that is packaged as Heavy Duty Tractor & Hydraulic Transmission fluid. The sales guy looked it up and said it was basically 10w. I am using it in both the fluid drive chamber and in the transmission. It seems to do the job. Desoto Joe

[Rusty_OToole]

A lot of us use TDH tractor fluid (stands for transmission, differential and hydraulic oil) ISO 32 grade.

It sounds to me like you have a wire shorting out when the tranny jumps around. Check the wiring carefully.

Marty I thought you fixed that? Your prob sounds like the kickdown switch on the carb is not working. It is supposed to "cut out" the ignition for a split second to allow the downshift. Again it sounds like a wiring prob or possibly the switch not making contact.

[De Soto Frank]

A Quickie test to determine if the problem of dropping out of gear is eletrical, is to carefull remove the floor mat, then the cover over the tranny, and disconnect the wires from the solenoid, and tape the terminal ends. ( The solenoid is the "big can" on the passenger side of the transmission case.)

Drive the car. You may have to use the clutch to assist in down-shifting at stops.

If the "dropping out of gear goes" away, then there's a good chance that the tranny's hydraulics & mechanicals are functioning correctly.

Reconnect the wires to the solenoid, and drive the car. If the drop-out problem returns, it is being caused by electrical issues.


A second vote for ISO 32 "Tractor Hydraulic Fluid" - found at some Wal-Marts and Sam's Clubs, as well as Tractor Supply Co. or other Farm stores.

Good luck !

[Rusty_OToole]

Frank will the transmission shift up with the wires off? Or will it stay in low gear of high range?

By the way Joe the TDH fluid is equally good for the fluid drive and the transmission.

[De Soto Frank]

Rusty, et al;

The function of the solenoid & related controls ( governor, kickdown switch, relay on '46-'48 models) is to control when the tranny achieves its automatic up-shift and / or down shift.

When the ignition is switched on, and vehicle is standing still, the governor points are closed, and the solenoid is energized, diverting oil from the transmission pump back to the case.

When you put the car into gear, and get under-way, the governor points open at about 7 - 10 mph, and the solenoid is de-activated.
Now the oil from the transmission pump is sent to the shifting piston, which moves and compresses a heavy spring against the direct-speed shifter fork/sleeve.
The up-shift doesn't take place until the driver releases the accelerator pedal long enough for strain on the gears to be relieved, allowing that heavy spring to move the direct speed shifter & sleeve, putting the car into the high-speed of that driving range.
( "Wait for the clunk." )

When car speed drops below 7-10 mph, the governor points close, the solenoid is energized, dumping the oil-pressure from the shift piston, and the tranny downshifts via internal spring.

So, whenever the solenoid circuit is enerigzed, the tranmission does not upshift, no matter how fast you're going or how long you leave your foot off the gas.

The tranmission does not need the electrical components to up-shift; only to down shift.