kaz1961

I have a 1980 with a 350hp crate 350 and a 68 date coded rebuilt TH400 tranny. The kickdown does not work, there is no kickdown switch by the gas pedal, whoever put in the tranny ran two wires with spade connectors to the solenoid connectors on the tranny. These wires go above the tranny but I cant see where they go. Is it possible that bubba hooked up the solenoid to some other location to get the kickdown to work?
I am thinking of just doing away with bubbas work and putting in a new harness and switch which leads me to other questions. I assume I need this harness since the tranny is a 68:

http://www.zip-corvette.com/68-69-au...g-harness.html

But the kickdown switch is labeled for 69-77's:

http://www.zip-corvette.com/70-77-th...ol-switch.html

Would that combo work together in my modded 80?

Any help and suggestions would be greatly appreciated.

99 Black Bird TA

I think the TH400 was vacuum controlled in 68 just like in my 72. There should be a vacuum line that looks sort of like the trap in a kitchen sink drain that connects to the kick down. If the line is there but doesn't have the funky trap shape it probably won't kick down correctly. I will look at my car and see if I can give a better description.

8valve

I have a 79 with a T400 that like yours did not have the kick down wired, Bubba got tired. I bought a B&M racing kick down switch.

The switch mounts aft of the carb. A small cable goes to the throttle arm. I picked up 12 volt power from the Acc fuse in the fuse block, this wire goes to one terminal on the kick down switch (either one). From the other terminal on the kick down switch run a wire to the terminal on the T400. Some T400's have 2 connections. Looking at the connection spades it looks like a 'T'. You attach the wire with a spade terminal to the VERTICAL bar of the 'T'. The horizontal top bar of the 'T' is not used.

You adjust the cable length at the carb so the switch is pulled fully just before you have WOT.

Thats it, really quick job. Summit Racing sells the B&M racing kick down switch. Have fun with the new kick down.

8Valve

croaker

I was just searching for my switch it's there but I didn't see my connector.

8valve

The T400 kick down connector (male spade lug) is on the left (drivers side) at the rear of the T400. Dont get hung up on the vacuum modulator which is on the right front of the T 400.

8Valve

7T1vette

THM-400 kickdown is an electric (12 vdc) solenoid mounted to the valve body plate in the tranny sump pan. Send 12v into that connector on the left side and the solenoid opens and the unit downshifts. (The transmission case must be grounded, but it's mounted to the engine so that should do the job.)

You just need to mount a switch somewhere on the accel pedal linkage (or the carb linkage) so that the switch is 'closed' (conducting) when the pedal/carb are at WOT. +12vdc into one side of the switch; the other side connected to the trans downshift connector pin.

kaz1961

My solenoid in the tranny has two connectors on it, a vertical one on the bottom with a horizontal one above it. Which one gets the 12 vdc hooked to it?

7T1vette

According to the Chevrolet Chassis Service Manual, the (lower) vertical pin is the 'detent' [kickdown solenoid] pin. The (upper) horizontal pin is the 'pressure switch' terminal. Putting power to the 'pressure switch' pin could damage the switch.

forvicjr

I just used a carb mounted nitrous switch. No downshift untill full throttle though.