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66 401 dual quad kick down & TH400 sp


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As I understand it With my 66 TH 400 sp both the kickdown and sp are electronic off the TH 400 is that correct. Do I still need a kickdown bracket ? Do I need a vacuum connection ? I am using after market Carters. I also understand the best way to enjoy the sp function relating to the stall, is to have the sp tied into the brake switch somehow, is that correct. Any advice is greatly appreciated .
 

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  • 2 weeks later...

I believe there will be TWO switches related to the SP THM400.  There will be a "kick-down" switch for that function, activated at WOT and also an "idle switch", which puts the converter into the "high stall" position to decrease "creep" at idle.  Once the throttle is opened, that switch is "open" (circuit-wise) and the converter goes into the default mode of "tight" for cruise economy and throttle response. 

 

On the normal THM400s, the kick-down switch can be either a plunger-style switch on the rear of the carburetor mounting or as a part of the accel pedal pivot on the inside of the firewall.  The "idle" switch should be on the front of the carb, in the same location as the later idle speed solenoids/throttle-kicker for a/c cars, to increase the base idle speed when the a/c compressor is running.  The normal THM400s will have one wire going through the trans case, driver's side, for the kick-down switch and another one in that grommet for the SP function.

 

When a SP THM400 was adapted to a car that did not have it from the factory, then a toggle switch for the SP function was usually used so you could run in SP mode when you wanted to, or when you chose not to.  The ONLY time wiring it through the brake light switch would work is when the brake pedal was depressed and NOT when the car was moving, so in that orientation, the whole SP mechanism would only work to stage the car ONLY.  From what I've seen, the "tight" stall speed for a 401 would be about 1700rpm, in the SP mode, about 2200rpm, with a "torque ratio" of about 2.7 vs about 2.1 in "tight" mode.

 

To verify the wiring and switch locations, you might consult a Buick service manual for 1966.

 

NTX5467

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