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1942 Fluid Drive - overdrive mystery?

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Hi I have recently bought a 42 Chrysler Windsor Coupe with fluid drive. Nobody seems to be able to tell me what the large chrome knob that sits beside the steering column. It's connected to a cable that runs to the transmission. However, I have been told that Fluid drives do not have overdrive, but I can't think what else it could be - I don't fancy engaging it when doing 50mph down the freeway. Any insight would be helpful. Mike 


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My 39 Chrysler has an OD trans but no fluid drive. When the OD is engages it will free wheel when coasting.

I read somewhere that you should never engage the OD while moving so that's what I do.

Have you tried driving the car with the knob pulled all the way out ?





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I don't know the model designations for Chrysler, so this is what The Hollander says. Was it called the "Underdrive" transmission? The case number cast in raised numbers on the trans. should be 868982 for '41-42 C30, 34, 36, 37. The same case is used with a different main drive gear in C28, C34 not 7 pass. (semi-auto trans.).


Here is what Wikipedia says about it: https://en.wikipedia.org/wiki/Semi-automatic_transmission#Chrysler


MoToR's Manual 1950 says the semi-automatic transmission used on 1941 Chrysler 8-cyl. cars combines an overdrive unit and a conventional 3-speed trans. in which low gear is blocked out. The automatic shifting feature performs much the same as the Vacamatic used in 6-cyl. models. However, in the low range shifts are between second and second o.d. while in the high range shifts are between high and high o.d..


If you can confirm the raised cast numbers and letters on the transmission case we can be sure. If there is an o.d., as indicated by MoToR, there will be an extension behind the trans. with R-6 or R-7 and other stuff cast on it. Can you read those castings to confirm what we are talking about? I expect there is an o.d. and the cable from the knob goes to a lever mounted on the side of it.


If you can tell me the vehicle model designation and whether it is a six or eight I can copy the pages from MoToR to here for you.


Can you reverse with the knob "in"? Usually with an o.d. you need to pull the knob to lock out o.d., but I am not familiar with o.ds with a governor, like that one.


I suggest you look for an owners manual about how to operate it. Don't pull the knob while moving until you know what it does.


"Fluid drive" is just where the clutch is in fact a torque converter.

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Your Winsor should be a 6 cylinder car with the "underdrive" transmission.  This transmission is a four speed unit, with the "low" gear position locked out.  The second gear position is the Low Range.  The transmission starts in first and shifts to second when you lift your foot off the gas.  The third gear position is High Range.  The transmission starts in third and shifts to fourth.  Fourth is drive, not an overdrive.  You should not slip the clutch to start out.  Depress the clutch, move the gear shift leaver to the range you want and release the cluch with you foot on the brake.  You're in Drive now.  Drive it like an automatic.  Only use the clutch when you need to move the gearshift leaver.


Now about that knob.  THIS IS NOT AN OVERDRIVE KNOB!   It is spring loaded and you must continue to pull on it to keep it pulled out.  It locks out the freewheeling used in the lower gears of each range so the car can be push started in an emergency.  Without pulling it out, the engine would not turn by driving the rear wheels.  Your owners manual and the service manual state that the knob should NEVER be pulled out while the car is moving or damage to the transmission will occur.


If you read the NOTE on the second page of "SpinneyHill"'s attachment it does a very good job of describing the use of this knob.


This does not apply to the 8 cylinder transmissions.  They are different although they drive the same way.


Yours looks like a nice car.....Enjoy the drive.

Edited by 61polara (see edit history)
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Many thanks for your replies and despite being told by the seller that it's an overdrive thank heavens I never pulled the cable out when driving, because as I have rightly been told this is not an overdrive, but moreover an emergency option when needing to tow or push start the car. I really appreciate your replies and special thanks to Spinneyhill for copies of the manual.

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