THM400 kickdown switch.
Thread Starter
1st Gear
Joined: Jan 2020
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THM400 kickdown switch.
Wife’s Christmas present 71 c3 w/THM400 only had a kick down passing gear BELOW 50mph! At 50+mph no kick down passing gear. Is kick down switch bad??? I bought on-line @ PATC $69 identical switch that goes above the gas pedal.Same results!!! Bad replacement??? Or are both switches good because,BELOW 50mph BOTH kick down???AND I need a BEER/break/solution.
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,335
From: North of Toronto - Ontario
The transmission doesn't know what rear end gears you have so it's not supposed to be speed dependent.
I'm guessing you set it up correctly? (pull all the way then trip with the gas pedal?)
Some have added rubber sleeves to the pin so they are a little less than WOT type of thing
M
I'm guessing you set it up correctly? (pull all the way then trip with the gas pedal?)
Some have added rubber sleeves to the pin so they are a little less than WOT type of thing
M
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The kickdown switch merely sends the 12 vdc signal to the detent solenoid inside the transmission. And that item only dumps pressure which SHOULD cause a downshift -- IF the speed is not so high as to overspeed the transmission, once that downshift is made. A WOT 3-2 downshift should occur somewhere in the speed range of 58-75 mph (specs shown in Chevrolet Chassis Service Manual at the end of the Turbo hydra-matic 400 section (Section 7). So, it should downshift above 50 mph. Causes for NOT getting that downshift (when other downshifts still function) are many. Most of them are internal to the transmission valve body area.
Race Director
Joined: Jul 2015
Posts: 13,082
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From: SW Florida.
i had a catalina conv i picked up for 300 bucks because the solenoid valve in trans was stuck open, so no upshift. if valve is stuck closed it will cause no kickdown downshift. easy to check. your wifey's trans needs a new filter and fluid anyway.
