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Kickdown Switch question  

Eminent Member

After driving my '46 with Fluid Drive for several years, I realized I had never tried to activate the Kickdown Switch. So on a recent weekly drive while going about 25 or 30, I tromped on the gas pedal. Car accelerated, but did not kick down into a lower gear. Then while going up a slight grade, I tried it again, and yes, tranny kicked into lower gear, however, the engine accelerated wildly but car did not speed up. It felt and sounded like it went into neutral. Have not tried it since. Any thoughts?  ( I should mention I previously had a '49 DeSoto and '50 Chrysler, both with Fluid Drive and used the kickdown feature with no problems.)

Posted : July 31, 2019 6:03 pm
Estimable Member

I'm no expert... but just wanted to know if you checked your Trans fluid?? Probably not the issue... but I thought I'd mention that. I have tried the "kickdown" on my 56 DeSoto Adventurer and it doesn't seem to KICKDOWN either. I have NOT yet to look into it!


Posted : August 6, 2019 1:53 pm
Estimable Member

Hi John,

Jim makes a good point.  The M6 "Tip-Toe-Shift" is very sensitive to transmission fluid.  It originally called for 10W engine oil, but Chrysler recommended changing it every 10,000 miles or 1 year.  That is reasonable if you are using engine oil, because 10W will quickly become 20W with use and that is too thick for the transmission's hydraulics.  I have tried various fluids with different viscosities and additive packages, and found that Type-F automatic transmission fluid works best.  It is a 5W-10 viscosity, has a lot of anti oxidation additives and extreme pressure lubricant additives.  Thinner stuff causes gear whine, and thicker stuff causes slow shifts, inconsistent downshifts and sometimes even a cavitation noise cold.

I wonder if your car might have something else going on though.  The 1946-1948 cars used a transmission kickdown relay which the 1949-1953 cars did not use.  Those relays can be troublesome.  There is a fuse associated, and the fuses can blow as well as the contacts getting burned or corroded over time.  If you coast the car very slowly into a stop, you should feel a noticeable downshift at around 8 MPH.  If it doesn't downshift until you are stopped, I would be suspicious that your relay isn't working.

As for Jim's car- well, he has a different transmission.  If his Powerflite isn't doing a kickdown, it is most likely the kickdown rod, or the kickdown piston.


This post was modified 7 months ago by BrentJacobsen

Brent Jacobsen
Owner of a 1952 Desoto Firedome

Posted : August 11, 2019 6:48 pm
Eminent Member

Ever since I got the car back on the road in 2012 or so, I have had no problems with the transmission shifting up and down under normal driving conditions.  Because of that, I have never checked the tranny fluid level.  Since then, I have driven the car 1000 trouble-free miles!

Posted : August 13, 2019 12:08 am
Estimable Member

90% chance the linkage at the carb is not adjusted correctly.  Also, I NEVER use transmission fluid as it can eat the brass rings. Not recommended.

I use the correct non detergent 10W as does my buddy with his '46 Chrysler T&C. Neither of us have ever had an issue traced back to fluid.

Go to the Imperial Club Website and the little service booklets online show you the proper trouble shooting steps.



Posted : August 13, 2019 5:50 pm