TH-400 help

AL8001 at aol.com AL8001 at aol.com
Wed Feb 24 01:21:32 GMT 1999


In a message dated 99-02-23 19:40:30 EST, you write:

>Possibly someone can help me with a TH-400 application.  I haven't ever had
>any dealings with these units, so I have a few questions...
>
>1.  The trans has a wire labeled "kickdown switch".  What does this do, and
>do you ground it or supply +12 to activate it? (I assume +12v, since there
>are no other wires and grounding could be through the case)

This wire is connected to a solenoid valve.  It drops the trans from third to
second gear when the throttle is over ~85%. Possibly to first as well, but I'm
not sure.   Just add 12V to operate, the solenoid grounds through the case.

A 400 with two wires has a pressure sensor to detect third gear ( for
emissions spark retard) or it's a mid '60s switch pitch trans.


>2.  Does anyone see any problems with deleting the speedo sensor, since the
>speedometer on my car takes its reading from the differential, and I'll be
>using a manual transmission calibration with the PCM... (96 LT1)  I think
>the only thing that a manual cal uses the speedo for is idle speed, and I
>can do without that.  Error codes aren't a concern...

Speedo Sensor?  Are you refering to the speedo cable port/ gear on the side of
the trans?  If so, not a problem.  Just use a freeze plug or a block off plate
from a 4 wd truck.

>3.  There's a modulator on the side of the case.  What does a modulator do
>when it sees boost pressure?  Should I use a check valve to block boost from
>going to it?
>
A 400 uses the modulator to generate throttle pressure and vary line pressure.
With limits, high line pressure at boost would be good.  Higher throttle
presure _may_ make the trans shift too late under boost.   Not sure if a check
valve would help.

>4.  How do you adjust the wide open throttle shift points?  I realize that
>the trans must be disassembled.

WOT shift points 1-2 and 2-3 can be moved upwards and downwards by changing
govenor weights and springs. Just take the four bolt cover off the side of the
trans to remove the gov.  You may need to have the trans on a slight down
grade to prevent fluid loss.    B & M sells the spring and weight kit.

To change the spaceing between the 1-2 and the 2-3 shift, the valve body must
be removed and the 1-2 or the 2-3 shift valve springs changed.  For the shift
kits I've seen, none alter the spaceing between the 1-2 and the 2-3 shift.
All concentrate on quick shifts and highter line pressure.
>Thanks a lot,
>Brock



Harold



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