TH-400 "sportmode"

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Adysthemic - 28 Feb 2008 00:53 GMT

Hello Group,

Any GM TH-400 automatic transmission gurus here? I ran across an idea whilst
looking
for info on a B&M Transpak kit. I installed the kit and love the change. The
new idea was to install a switch in parallel with the TH-400 "kickdown"
switch, that would allow you to "turn it on and leave it on". Here's the
theory... If you actuated that switch, under
light throttle,high vacuum, wouldn't it still shift "normally"? THEN if you
drove harder wouldn't it then hold each gear to the customary "kickdown"
5000 rpm before a shift taking place?
IF it does indeed work this way, would it hurt anything? You could just
switch it on or off. Since the switch is in parallel, turning it off would
just put it back to "normal" mode.
Is my logic off on this concept, or am I missing something stupid and
obvious?, Thanks
Adysthemic

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Kevin - 01 Mar 2008 20:26 GMT

> Hello Group,
>
[quoted text clipped - 14 lines]
> obvious?, Thanks
> Adysthemic

There is no point in doing this. It will not shift normally if the
kickdown is switched on no mater the throttle setting. that is what the
kickdown switch does. if the kickdown switch is working ok you do not
need any other mod. KB

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Adysthemic - 02 Mar 2008 02:07 GMT

>> Hello Group,
>>
[quoted text clipped - 19 lines]
> kickdown switch does. if the kickdown switch is working ok you do not
> need any other mod. KB

Erm,uh, I don't want it to shift "normally" in this mode. I would like it to
hold each shift
to 5000rpm, then shift. Then I'd like to flip a switch and go back to
"normal". I believe that I have analyised the "problem" as thoroughly as I
can. Perhaps you do not fully grasp what I am inquiring about. Adysthemic

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Rodan - 02 Mar 2008 02:32 GMT

Perhaps you do not fully grasp what I am inquiring about.
_______________________________________________

Tell it like it is, Adysthemic. You're sure to get a lot of
advice and help that way.

Rodan.

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Steve W. - 02 Mar 2008 04:08 GMT

>>> Hello Group,
>>>
[quoted text clipped - 25 lines]
> "normal". I believe that I have analyised the "problem" as thoroughly as I
> can. Perhaps you do not fully grasp what I am inquiring about. Adysthemic

Won't work that way. With the kickdown engaged the trans won't shift.
The kickdown solenoid only diverts fluid. If you try to engage it in
other gears it will act like it's in neutral.

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Steve W.

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Adysthemic - 03 Mar 2008 00:09 GMT

>>>> Hello Group,
>>>>
[quoted text clipped - 30 lines]
> kickdown solenoid only diverts fluid. If you try to engage it in other
> gears it will act like it's in neutral.

Steve,

Do you think just trying out my theory will have any delitrious effect, or
will it just not work? I want to "turn on" the kickdown switch, leave it
that way, and drive around
in a spirited manner. I theorise that each gear will hold to the limit of
the mechanical governor,then shift, when throttle position is such that the
vacuum modulator sees little
signal due to wide throttle opening. I also think that driving very gently
would produce
no discernable difference in tranny behaviour. What do you think? Would
trying this
hurt anything? Adysthemic

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Steve W. - 03 Mar 2008 00:24 GMT

>>>>> Hello Group,
>>>>>
[quoted text clipped - 43 lines]
> trying this
> hurt anything? Adysthemic

Good way to burn out the clutches through the slipping when they don't
get full pressure because of the diversion from the KD.

What you are attempting can be done but it isn't a simple thing. You
would need to alter the governor and the valve body so that you would
still have full pressure shifts. The other item is that unless you have
an engine that can handle those shift points you will probably snap the
crank on about the third shift. The engine is going to be way off the
torque peak when the shift occurs which will mean instant lugging and
constant hunting as it tries to keep up to speed. It will act a lot like
an impact wrench connecting the engine and the trans. Even the converter
won't help much unless you replace it with a very high stall to help
absorb the shock of the shifts.

In all I wouldn't even try it unless you want to buy a new transmission
really soon. And possibly a new engine as well.

Signature

Steve W.

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