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#1 |
Senior Member
![]() Join Date: Feb 2022
Location: Ca
Posts: 496
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Kickdown system education needed
After 50+ years of hot rodding, this is my first automatic transmission I’ve owned. After doing some research I am not 100% sure on a few details of the TH350 kickdown system. As I understand it, there are 2 switches, so to speak, that will drop the transmission down from drive to 2nd. One is the vacuum module that, as I understand, limits the line pressure in the transmission to delay shifting further up the RPM range or down shifting when a low vacuum state is achieved under heavy engine load. I am guessing there is some sort of mechanical weight governor as well to work in conjunction with the vacuum module. The kickdown cable is a little less clear to me. Does the cable modify the vacuum signal which in turn affects line pressure and ultimately shifting? Or, is there a second valve in the pressure line adjusted by the kickdown cable directly. Is this kickdown cable system variable or like an on off switch closing a valve at the last bit of throttle travel?
The modifications I am currently in the middle of will need to eliminate the kickdown cable. Can I use a micro switch to trigger a solenoid activated vacuum valve to close the vacuum line to the module and get the same down shift result? Is this how a TH400 works, given there is an electrical switch involved with that transmission? |
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#2 |
Senior Member
![]() Join Date: Jun 2022
Location: San Ramon,CA
Posts: 497
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Re: Kickdown system education needed
TH350 actuates a valve directly.
IIRC, 400 is also valved, but a switch on the carb triggers a solenoid to open it https://www.onallcylinders.com/2014/...like-3-speeds/ I Stole this snippet from Ken Ruggles' book, (which has a whole section on performance mods, but I ain't never done that):
__________________
1970 C10 Custom longbed 350/350 |
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#3 |
Senior Member
![]() Join Date: Feb 2022
Location: Ca
Posts: 496
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Re: Kickdown system education needed
got it. Thanks Rust. So now I need to engineer a solenoid setup that will pull the cable at WOT. Anyone know of a kit?
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#4 |
Senior Member
![]() Join Date: Mar 2015
Location: washington
Posts: 2,233
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Re: Kickdown system education needed
The THM350 only requires a cable and bracket to be functional. Nothing electrical.
You can run without it but it will lack the crisp down-shift it will have with it working. The 700R4/4L60 has a TV cable and has to have it connected and functioning or it will immediately trash the transmission. The 700R4/4L60 has a TV cable looks like and connected the same as the kick-down cable but the function is completely different. Unless. by chance, you have a THM350C with the lock-up converter and you want that to function. It is electrically powered. Last edited by Accelo; Today at 02:23 PM. |
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