T 400 kick down?

[lux]

I'm building a 69 short bed. I have a 10.4/1 compression 383 built for it, guessing around 450 hp. B&M ratchet shifter. 2700 rpm stall speed. Not sure about the rear end gear yet.
Do I need to worry about hooking up my kick down switch on the t400?
Not planning on hauling anything.

[AussieinNC]

Originally Posted by lux

I'm building a 69 short bed. I have a 10.4/1 compression 383 built for it, guessing around 450 hp. B&M ratchet shifter. 2700 rpm stall speed. Not sure about the rear end gear yet.
Do I need to worry about hooking up my kick down switch on the t400?
Not planning on hauling anything.

If you intend to drive the vehicle in D, yes....as the TH400 lacks any direct throttle input so it doesnt know what load is on the vehicle...

If you are installing a manual shift system, (you mention a B&M ratchet shifter) then no you dont...but trust me, on a long drive in city traffic you might want to reconsider the manual shift setup...

Hope this helps...

[lux]

Thanks,
I do plan to select drive most times.
I guess I really don't understand the function of the Kick Down. The way I understand it, while driving and engaging wide open throttle the trans will change from 3rd to 2nd for passing.
I think with the horsepower of this engine passing shouldn't be a problem.
And if it is I'll just use the ratchet shifter to drop down to 2nd.

Is the kick down doing something more that I'm not aware of?

[AussieinNC]

Originally Posted by lux

Thanks,
I do plan to select drive most times.
I guess I really don't understand the function of the Kick Down. The way I understand it, while driving and engaging wide open throttle the trans will change from 3rd to 2nd for passing.
I think with the horsepower of this engine passing shouldn't be a problem.
And if it is I'll just use the ratchet shifter to drop down to 2nd.

Is the kick down doing something more that I'm not aware of?

The kickdown does one thing only...drops the trans to a lower gear for passing....

The vacuum modulator controls shift feel
The governor controls shift points

There is no throttle valve (TV) cable on a TH400 trans...

[Dead Parrot]

You could run the wires that normally go to the kickdown switch to a push button on your console for downshifting when needed. That way you don't risk missing D and winding up in N when recovering from a manual downshift.

[lux]

Originally Posted by Dead Parrot

You could run the wires that normally go to the kickdown switch to a push button on your console for downshifting when needed. That way you don't risk missing D and winding up in N when recovering from a manual downshift.

A ratchet shifter keeps me from going into Neutral.

[lux]

Originally Posted by AussieinNC

The kickdown does one thing only...drops the trans to a lower gear for passing....

The vacuum modulator controls shift feel
The governor controls shift points

There is no throttle valve (TV) cable on a TH400 trans...

Great that's what I thought. But, will I do any harm to the transmission by not using the kick down?

[AussieinNC]

Originally Posted by lux

Great that's what I thought. But, will I do any harm to the transmission by not using the kick down?

Consistent use in 3rd gear where you should be in 2nd can escalate clutch pack wear...

The suggestion of a push button to activate the kickdown seems the simplest way to keep it active...maybe place the button on the ratchet shifter.

I assume the trans builder is adding clutch plates in the build....

[lux]

Thanks for the info. I'm going to try it for a while without the kick down. I'll add it later if I feel I need it.

[cadillac_al]

I drove a car for a few years without the th400 kickdown hooked up. This was due to pure laziness. It worked fairly well and the governor pretty much keeps it in the right gear. If you have lots of power and not geared too high it will work fairly well. The kickdown is so simple to set up there isn't much reason not to have it. The aftermarket makes a lot more switches than they did 20 years ago. A simple switch mounted on the carb is pretty universal.

[lux]

Would a switch at the gas peddle be easier or the carb?
Does the switch work by simply completing a circuit or does it require power?
Thanks for your help guys, I'll do some research on this as well.

[lux]

Now that I'm really looking it over, I realize that it's not that difficult.
Yes, it does require 12vdc to activate.
Apparently not hooking it up can cause damage. I found a nice article on the subject.
https://www.onallcylinders.com/2014/...like-3-speeds/

It says;
"Often when a TH400 is swapped into a different vehicle, this downshift electrical switch is overlooked. Besides the loss of any kind of downshift function, the real danger is that under WOT the transmission has not been commanded to increase line pressure. This causes not only a soft upshift, but also damage to the clutches because the lower line pressure increases the potential for slippage on upshifts. There are several ways to solve this problem."

I'll take it as a small challenge, after all fabrication is fun.

[Ben IV]

I'm using the lokar setup.

[Troy Sr]

Here's the B&M Version


https://www.summitracing.com/parts/bmm-20297

[lux]

Now I have to figure out the vacuum modulator hook up.
As best I can tell it is a vacuum line from the intake manifold to the transmission.

[AussieinNC]

Use full manifold vacuum source, usually the same fitting at rear of manifold that runs the brake booster...

Use can use simple rubber tube suitable for vacuum use...and connect to the modulator...

Make sure the modulator is ok....

If you all of a sudden get lots of smoke out of the engine once the modulator is connected...its usually broken diaphragm inside the modulator.

[Troy Sr]

Here's a fitting that can be used for the brake booster and the vacuum modulator.

https://www.summitracing.com/parts/clp-in38rs

[lux]

Thanks guys,
It's a new trans so I hope the modulator is good.
I'm using a hydro boost brake system, so that vacuum line off the manifold will be available for the modulator alone.