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Hi all, I'm hoping for clarification on a fluid drive question. My car has a push button on the end of my gear lever. I was told by the previous owner that is in how to shift from 1st to 2nd, and 3rd. Unlike how the manual says about it doing it automatically when you let off the gas pedal. The little bit I could find on the internet says that it was an option, either factory or aftermarket from Mopar. But it doesn't say much more. Any help understanding this would be very helpful. Also, I'm not sure is the car is a three speed or four. The previous owners son told me three, but videos on YouTube say four. I'm also not sure if I'm shifting properly. I've been a Mopar guy all my life, but this is my first fluid drive. Thanks for the help.
Hi there @raydevlaminck . It sounds like you are off to a good start and welcome to the DeSoto forums! (I apologize in advance for the lengthy response, but I wanted to thoroughly cover this topic and answer all of your questions the best I could). I own a 1941 and 1948 DeSoto, both with semi-automatic transmissions. I have researched these semi-automatic transmissions quite a bit over the past few years, so I can hopefully answer a few of your questions and give you a background on how they operate. The Chrysler corporation offered both a 3-speed and 4-speed transmission paired with a Fluid Drive coupling. You will see a LOT of people incorrectly call these "Fluid Drive transmissions". There is no such thing! The Fluid Drive is not part of the transmission. The Fluid Drive is a coupling between the engine and transmission that allows you to come to a complete stop without pressing the clutch in and without stalling the engine.
All three speed transmissions paired with a Fluid Drive functioned, and for the most part, were driven like a conventional three speed column shift transmission. With the exception that you would not have to depress the clutch when coming to a stop in any gear. Also, you could technically take off in any gear with the 3-speed transmission, but it would be slow going.
All four speed transmissions paired with a Fluid Drive were semi-automatic transmissions. The Chrysler corporation made several variations of the semi-automatic transmission, and every branch, Chrysler, Dodge, DeSoto, and eventually Plymouth, all had unique names for the same transmission. So it can get quite confusing!
For now, I'll start you off with this, ALL Fluid Drive DeSotos came with semi-automatic 4-speed transmissions. There were three variations of the semi-automatic transmission for DeSoto, code names M4, M5, and M6. The M4 was called the "Simplimatic transmission" (1941 & 42). Both the M5 (1946-48) and M6 (1949-53) transmissions were called the "Tip-Toe-Shift transmission". Parts and electrical components DO NOT interchange between the three variations! Fortunately, however, many of the electrical components (solenoid, governor, and interrupter switch) for all three variations can be found fairly easily.
Being that your DeSoto is a 1950, it should have the M6 Tip-Toe-Shift semi-automatic 4-speed transmission. As you have likely read, there are two forward moving "ranges" with these transmissions. Low range includes 1st and 2nd, which is selected by moving the gearshift lever to the position that 2nd gear would be on a conventional column shift 3-speed transmission. High range includes 3rd and 4th, which is in the gearshift position that 3rd gear would be. Reverse is in the normal location (towards you and up), and the normal 1st gear gearshift position is not used and is blocked out.
While it is technically a 4-speed transmission, you do not shift it 1-2-3-4. There are a few different ways of operating it depending on who you ask and their preferred driving style. You can drive it as the Chrysler corporation intended, which is to put the gearshift in High range and leave it there and just shift between 3rd and 4th by completely lifting your foot from the gas pedal for a few seconds and waiting for an audible click or clunk. Alternatively, you could start in Low range 1st, accelerate a bit, completely let off the gas until you hear a click into 2nd, accelerate a bit more, then clutch-in, move the gearshift to the High range, clutch-out, and you'll be in 4th. You can also start in Low range 1st, accelerate a bit, clutch-in, move the gearshift to the High range, clutch-out, you should be in 3rd, accelerate quite a bit, then let off the gas, wait for the click, and you should be in 4th. The transmission will automatically downshift from 4th to 3rd or 2nd to 1st (depending on the range you are in) when you slow down to a predetermined speed. If you want to force a downshift when in the higher gear of either range (2nd or 4th), you can floor the gas pedal, which makes the throttle linkage come in contact and depress a button on the carburetor that sends an electrical signal to the transmission components and forces a downshift to 1st or 3rd.
Getting to what the push button on the end of your gear lever is. It is likely something called a "Shift-Rite". I don't believe it was a factory accessory, but there were several aftermarket companies that made "Shift-Rite" knobs, so there are a few different designs out there. It replaces the factory gearshift knob. I have never seen or used one in person, but from my understanding, it only has one wire coming out of it and it connects somewhere into the interrupter circuit of the transmission harness. You would ONLY use the "Shift-Rite" to force a downshift, it would never be used to initiate an upshift.
Some people installed a "Shift-Rite" to have better control over what gear they were in. Some installed it so you don't have to floor the gas pedal if you want to downshift from either 4th to 3rd or 2nd to 1st before you reach the predetermined speed slow enough for the transmission to downshift automatically. Or, it is possible that the previous owner(s) may have installed a "Shift-Rite" as a band-aid to an actual problem. These semi-automatic transmissions are fairly reliable, and in most cases, when something goes wrong, it is typically with the wiring/electrical components that control the transmission, rather than something internally wrong with the transmission. If the transmission harness hasn't been replaced, the newest factory wiring harness is, at best, 71 years old. Rhode Island Wiring sells reproduction transmission wiring harness, but make sure you get the correct one for the version of semi-automatic transmission you have (that is only if you need one), as the wiring harnesses are completely different depending on M4, M5, or M6.
Hopefully this helps clear up some of the questions you have. I know this was a bit of a long-winded response, but I wanted to break it down in simple terms for someone just getting their feet wet with the Fluid Drive and semi-automatic transmissions. If you have any further questions, please don't hesitate to ask, I have lots more Fluid Drive related knowledge I can share!
Carl
Carl, don't apologize for the long response, I appreciate all the useful, information! It gives me a good beginning understanding of the transmission, and fluid drive operation. I dropped my car off today at the Jack Frost automobile museum to have some light damage from its cross-country transport repaired. (The transport company is paying). The manager there, had never seen or heard of the shift rite and was interested in learning about it as well, so I will print your reply for him. If I can figure out how to post a picture on here, I will take a picture of the drive rite so you can see what it looks like.
I sold my 74 Dart, and 46 Hudson to buy this car, and so far have not been disappointed. I love driving it I've wanted something from that era that was original for a long time. Eventually I'll finish my hot rod, ( a 34 Ford 2 dr sedan),and have the best of both worlds.
The manager at the museum told me he was very impressed with it, and actually said it belongs in a museum. I was shocked, and happy. I've joined the great lakes chapter, and am looking forward to the events. I'm planning on being at the national convention as well. It sounds like a great time.
I'm sorry to hear that your DeSoto was damaged in transport, but I'm glad to hear that the shipping company is working with you to repair the damages. I am pleased to hear that you got some valuable information from my post! As I said, if you have any further questions on the Fluid Drive or Tip-Toe Shift transmission, please don't hesitate to ask.
As you may know, Glenn Colburn is the president of the Great Lakes Chapter. He is a really nice guy! I have very much enjoyed the conversations I've had with Glenn at all of the past NDC Conventions I have attended. He owns a 1959 DeSoto Firesweep 2-Door Hardtop. He has driven it to countless conventions, no matter the distance, since I believe the early 2000's.
I am excited to hear that you are planning to attend future NDC Conventions! The convention for 2025 is going to be in Akron, Ohio. I have every intention of driving my 1941 DeSoto DeLuxe 2-Door Sedan to next years convention...if I can get it back together in time...😳 It is currently in many pieces, as the entire front suspension, steering components, and steering gearbox are totally disassembled. I was trying to repair some excessive slop in the steering, but one thing lead into another, and here I am rebuilding the entire front end! I am optimistic that it should handle very well once it is all put back together. It's just a matter of if I can get it all reassembled before June 2025, as I do all of the work on my DeSotos myself.
Carl
"Shift-Rite" - I learned about something completely new (to me) today!
@davidfrank it's always a good day when we learn something new!
@carlnutaitis Carl, I pick my car up from the museum today. They were able to take care of the repairs. I'm so exited to drive it one more time before I leave for deer camp, and the cold weather hits. I found some original key blanks,and some cool old DeSoto key chains for them, so I'll get them cut on the way home, ( it only came with one set.) I'll snap a Pic of the drive rite when I get back home.
@raydevlaminck I'll bet that feels good to have that resolved before winter!
@carlnutaitis I got my car back,and they did a fantastic job! The paintless dent guy was great!. And the scratch turned out really nice! I'm trying to send pictures, of the drive rite but I live in the sticks, and it's storming here.
@davidfrank Yes, it's was nice to get it back before the weather turned bad. I took her for a spin yesterday, and washed it and covered it up for the winter. I'll spend the winter months finishing up my flat bed dually shop truck, and continue work on my 34 Ford.
@raydevlaminck Thank you for taking a couple photos of the "Shift-Rite" knob! There is very little information about the "Shift-Rite" knobs on the Internet and very few photos of the knob installed on a car, so I appreciate you sharing the photos!
I'm glad to hear that the repairs to your car from the shipping damage were taken care of in a timely manner and are resolved before Winter. It's great that a paintless dent guy was able to repair your car, instead of having to send it to the all too familiar, especially for old cars, "body-shop prison".
