How to operate Tip-Toe Shift transmission c.1946

[marcapra]

I've seen many videos on Youtube where the owner of a semi-automatic Mopar does not quite know how to drive it. They often just drive like a 3 on the tree. So I'm including a little folder that came with new DeSotos in 46-49 to instruct new owners on how to drive with the semi-auto M5 transmission.

 

 

[mrspeedyt]

My 41 DeSoto had the earlier version of that transmission (fluid drive simplomatic ) and had its own idiosyncrasies that were corrected with the later version.

[marcapra]

I'm curious, what needed to be corrected with the 41-42 semi auto transmissions?  Was it a vacuum leak?  

[c49er]

Early Simpli-Matic transmissions used  rubber diaphram using vacuum to shift into high gear.

The rubber diaphrams were prone to failure so the piston type came out in late 1941.

Ii was a 4" vacuum cylinder with a large piston and leather wiper seal.

a much better trouble free design.

 

[mrspeedyt]

also, in the early simplamatic transmission of the 41 DeSoto, has a ratchet mechanism for splitting the two forward gears and frequently that ratchet mechanism wears out with use  and you have to pull the knob under the dash (which is the same kind of looking knob as a overdrive unit on other cars) to lock out the ratcheting mechanism... so in effect you have only two speeds... low and direct instead of four speeds. it honestly is not a very good transmission because of this. on the otherhand... the clutch of the fluid drive works reliably.

 

the foot clutch is used to put the transmission in gear and then you release the clutch and let the fluid drive do its job to move the car from a stop. also I use the foot clutch when I am shifting from low to high. you don't have to feather the clutch in any situation. it's just basically in and out.

 

so most of the time I would drive the car using the two speeds low and direct and if stopped on a slight downgrade I might just leave it in direct while I'm stopped and when taking off. it's a slow long acceleration but eventually the car moves on down the road. it's probably the slowest thing imaginable to accelerate with in direct drive.

Edited October 10, 2023 by mrspeedyt (see edit history)

[marcapra]

So the prewar m4 transmissions only have Low and High with nothing in the middle after that rachet thing wears out?  If it can't be repaired, that doesn't sound too good.  Sounds like what you are saying is that there is no automatic shifting within the two speed ranges, low and high range on 41-42 MoPars.    

[mrspeedyt]

yeah.  if the ratchet thing is worn out basically it's just a two-speed transmission.

[61polara]

The knob under the dash on the pre-war versions was to be pulled out when push starting the car only.  It is spring loaded and must held out against the spring and returns as soon as it is released.  The owners manual and service manuals state that the knob should never be pulled out while driving or transmission damage will occur.  Pulling out the knob locks a one way roller clutch in the lower range of either gear so that it does not freewheel and the car can be push started in first (low-low) or third (low-high) gear.  I believe the post war transmissions still have this one way roller clutch, but changed the instructions on push starting to eliminate the knob.  Both of these transmissions free-wheel in the lower gear of each range, but become non-freewheeling when in the higher gear of each range.  Push starting a post war car you are to get up to at least 15 MPH and then release the clutch.  This is because the governor points will have opened and the transmission will be in the higher gear of the range.

If the one way roller clutch is worn out, it's time for a transmission overhaul to prevent further damage to the transmission.

 

Driving the pre and post war transmissions is the same.  The high range is adequate for 90% of all driving and is not sluggish.  Better off the line performance can be had by starting in low range and manually shifting to high range.  This is a very flexible transmission and it does not damage it to start in low and shift to high.  Shifting this way you can choose, through the accelerator to hit gears 1-2-4 or 1-3-4.  Overall, it's a very simple transmission that is very trouble free.  Slipping the clutch on a start all the time will quickly wear out the clutch as it is a small unit and not designed to be slipped for a start.

[1950sportman]

I have a 1950 DeSoto Sportsman 

 

I have found in my life that diagrams and reading up on something before I tackle a problem is better than getting half way done and then looking for answers 

 

What I have read is the tip toe transmission has electric over drive

 

I have read the electrical and transmission section of my repair manual and neither has a wiring diagram for this function

 

Does anyone have a service manual with this diagram or even a scratch on a napkin of the wire routing for the electric part of the transmission 

 

 

Thank in advance

[c49er]

The DeSoto TipToe M-6 transmission does not have overdrive...no and no.

It's just a Hydraulically operated Hi/Low  two range four speed transmission. Direct in forth.

Exactly the same the 1949-53 Dodge and Chrysler M-6 transmission.

[Rusty_OToole]

4 hours ago, 1950sportman said:

I have a 1950 DeSoto Sportsman 

 

I have found in my life that diagrams and reading up on something before I tackle a problem is better than getting half way done and then looking for answers 

 

What I have read is the tip toe transmission has electric over drive

 

I have read the electrical and transmission section of my repair manual and neither has a wiring diagram for this function

 

Does anyone have a service manual with this diagram or even a scratch on a napkin of the wire routing for the electric part of the transmission 

 

 

Thank in advance

Slight misunderstanding here. There is no overdrive, there is a 4 speed transmission with direct drive top gear. Shifting is done by a hydraulic piston driven by a pump on the back of the transmission. The shift is controlled electrically.

There is a manual shift to select Low range, High range or Reverse. Then there is an automatic 1-2 shift in Low range, and an automatic 3-4 shift in High range.

Here is the wiring diagram. Power is tapped from the coil. There are 2 on-off switches on the carburetor, one for full throttle one for closed throttle. Then there are 3 controls on the trans, the governor, solenoid and interrupter switch. Below the interrupter switch you can see the hydraulic piston that slides the shifter fork back and forth.

 

[61polara]

Chrysler helped with confusion on their various transmissions offered in the 1940's and early 1950's.  I just pulled out my 1940-48 Chrysler factory shop manual and here are the sections I find relating to transmissions:

 

Fluid Drive - This is covered in the clutch section and is only the fluid coupling used either with a standard 3 speed transmission or a semi-automatic transmission.  Available on Chrysler, DeSoto and Dodge, but not Plymouth.

Three Speed Manual Transmission - no automatic shift.  A standard 3 speed transmission available with standard clutch or Fluid Drive coupling.

Vacamatic Transmission - This is the prewar version of the semi-automatic transmission that is vacuum shifted.  In Chrysler cars, this was called Vacamatic, in DeSoto cars it was called Simplimatic.  Same transmission, just different names for marketing.  Overdrive was not available on this transmission.  It was not available on Dodge or Plymouth.

Vacamatic Overdrive - This is where it gets confusing.  It appears it was available on the C-30 and C-33 1941 Chryslers.  It appears to be an overdrive unit on a standard three speed transmission and is cable controlled by a knob on the dash.  Pushed in gives overdrive operation and pulled out locks out overdrive.  It operates just like a normal Borg-Warner overdrive.  The confusion is that Chrysler refers to it as Vacamatic Overdrive.  From the diagrams, this is not vacuum controlled and is not available on the semi-automatic Vacamatic Transmission.

Hydraulic Operated Transmission - Post war the semi-automatic transmission changed to being shifted by hydraulic pressure rather than vacuum.  The operation of the transmission remained the same.  Overdrive was not available on this transmission.

 

To further confuse things, I've seen other MoPar manuals describe the semi-automatic transmissions as Underdrive and Overdrive semi-automatic transmissions.  With the post war semi-automatic transmission different transmissions were used for the 8 cylinder cars and the 6 cylinder cars.  The 8 cylinder car used a three speed transmission with the low range blocked out.  In Low Range it shifted from second to second overdrive.  In the High Range, it shifted from third to third overdrive.  The top gear was not a true overdrive but a 1:1 ratio.  Overdrive only described the method of shifting.  For the 6 cylinder cars, a four speed transmission was used.  In places I've seen these gears described as second-underdrive and second gear in Low Range and third-underdrive and third gear in High Range.  Again, the highest gear was a 1:1 ratio.

[Rusty_OToole]

You can go nuts trying to figure out the welter of transmissions used on Chrysler products 1939 - 1954.

[marcapra]

16 hours ago, 61polara said:

To further confuse things, I've seen other MoPar manuals describe the semi-automatic transmissions as Underdrive and Overdrive semi-automatic transmissions.  With the post war semi-automatic transmission different transmissions were used for the 8 cylinder cars and the 6 cylinder cars.  The 8 cylinder car used a three speed transmission with the low range blocked out.  In Low Range it shifted from second to second overdrive.  In the High Range, it shifted from third to third overdrive.  The top gear was not a true overdrive but a 1:1 ratio.  Overdrive only described the method of shifting. 

AS far as I know from reading Chrysler shop manuals, the 8 cylinder Chryslers from at least 41 to 50 used the same M-4,5, and 6 transmissions as the 6 cylinder transmissions.  

[61polara]

The prewar Vacamatic Overdrive transmission was used in the 8 cylinder Chryslers and was made to drive like the 6 cylinder semi-automatic Vacamatic.  This was a 3 speed overdrive transmission with the low position blocked so you could not place the transmission into the 1st gear position.  So the shift controls for driving were the same as the 6 cylinder car.  In low range it shifted from second to second overdrive and in high range shifted from third to third overdrive.  Just like in the 6 cylinder cars, you had to lift your foot off the gas for the shift to occur.  It appears this transmission had a lockout to disengage the overdrive function.  Since it was actually a 3 speed transmission (the gears are there, just not used) it was possible to remove the block on the first gear position and then have first and first overdrive.  This transmission would also shift into reverse overdrive if you were over the cut over speed and lifted your foot off the gas.  Note that the M-4 was not available on the prewar 8 cylinder Chryslers, so this was used to make the 6 and 8 cylinder cars drive the same.

Edited December 12, 2023 by 61polara (see edit history)