T400 questions (horse isn't quite dead yet)

[Luvlegs]

I have the original 454/400 that was pulled from a 73 ElCamino SS - the tranny needs to be rebuilt so it'll be a while before I actually get around to installing it.

Question 1 - What/Is there a difference between a T400, TH400, etc or are
they all the same thing? (I keep seeing them called several
different names)

Question 2 -A I have been told it doesn't have overdrive (ok..) but I keep
seeing "kick down" this and "kick down" that, related
400s.... what am I missing, is that just a drop down in gears to
pass thing?
B I had a 400 tranny behind a 400 in a 67 pontiac - I dont
remember anything connected to it but the speedo..... am I
missing something? The car was killer and I didn't notice
anything possibly wrong....

Question 3 - What are all the parts related to the linkage for the 400 on our
trucks? Rod, frame bracket, ??? Anyone have any pics of all of
them together?

Question 4 - What are all the parts/linkages related to install the kickdown
(or do I even need it?) and again, does anyone have pics of
them all together?
Thanks all!

[Jayss109]

#1 All a Turbo Hydromatic 400 (all the same) some have different bellhousings (non chevy)

#2 Detent switch/kickdown. So when you step on the gas, the transmission down shifts automatically

#3 Havent a clue, Im using a floor shifter with my TH400, maybe someone else can help with this one

#4 a micro switch mounted to the carb is the most common. Just a 12 volt switch, that when the throttle is open 80-100%, sends 12 volts to the TH400, telling it to downshift. Again, no pictures, mine is on the button on my floor shifter handle.

TH400s are getting more rare, find a GOOD trans shop and have them do it up right for you. expect to pay $1000 for a full, proper rebuild.

Jason

[Luvlegs]

Thanks Jays. Anyone have anything they can add? Once the tranny downshifts, at the 80-100 WOT, if you hold the throttle in, what allows it to upshift? do you have to let off for it to do it?

[1970bowtie]

Originally Posted by Jayss109

#1
TH400s are getting more rare, find a GOOD trans shop and have them do it up right for you. expect to pay $1000 for a full, proper rebuild.

Jason

just by a new th 350 from tci, it'll hold up to a 454

[Luvlegs]

I'm almost done building my 454 - spec'd to make 500 at the crank - I figured I'd be better off having the 400 built up to it...

[BACKYARD88]

Originally Posted by Luvlegs

Thanks Jays. Anyone have anything they can add? Once the tranny downshifts, at the 80-100 WOT, if you hold the throttle in, what allows it to upshift? do you have to let off for it to do it?

It will manually upshift itself if everything is operating correctly.

[mrein3]

Originally Posted by Luvlegs

Thanks Jays. Anyone have anything they can add? Once the tranny downshifts, at the 80-100 WOT, if you hold the throttle in, what allows it to upshift? do you have to let off for it to do it?

My understanding is Yes - you have to let off. If you hold your foot down past the "on" position of the switch in relation to the throttle, it will hold it in that lower gear indefinately.

Same thing on a th350 only on the 350 the "kick down" is a cable connected to the carb.

I've tested this with the th350 behind the 383 in my truck. I get scared and let off WAY before the tranny has a chance to do anything.

In the original owners manual in my Chevelle (again a th350), it says L2 can be shifted to at ANY speed. This implies that if I'm going 120mph and stomp on it, it will down shift. I'm not testing that.

I hope this helps.

[Jayss109]

Keep the TH400! They are all but bullet proof!!

The vacuum modulator/governor it what allows for the upshift to occur after a full throttle blast. Some can be adjusted to change when it will upshift. (keep the rpms at a safe level)

The detent/kickdown switch raises the fluid pressure as well. This helps with excesive slip/wear on the clutches and bands.

If you are worried about it shifting "right", do what I do. When I know IM gonna get on it (racing, passing, or just want to shut somebody down), I hit my manual detent button, and use the B&M floor shifter to bang through the gears.

Remember, you will ALWAYS be smarter than your transmission! lol

Jason

[KFreddy]

This a cut and paste from an earlier post a few weeks ago, it should answer your questions.

The Th400 is factory calibrated to shift between approx 3000 and 4800 RPMs dependent on the original factory application/ rear end gear.

Three things determine shift points, the transmission vacuum modulator, the transmission governor and load/speed.

The vacuum modulator is located on the passenger side just next to the tranny. It has a set screw on it, this is good for minor shift point/ speed adjustments. High vacuum: soft and early shifts, lower vacuum firm and later shifts. I say minor adjustments because this is all in relation to available vacuum. Low throttle = lots of vacuum, high throttle = little or no vacuum, hence the tranny shifts at higher RPM when vacuum is low. You really can't adjust the vacuum when there is none. Ultimately the vacuum modulator is only good for adjusting part throttle upshifts, 200 to 400 RPMs at best, it will not affect WOT upshifts.

More importantly is the transmission governor, it overrides the vacuum modulator at about 3/4 to WOT (again because at high RPM there is little or no vacuum.) The governor is located at the rear of the main Trans case on passenger side on a Th400. The transmission governor is controlled by the detent switch (kick down switch) that is usually located on the gas peddle of a Th400 equipped car or truck, unfortunately factory detent switches are non-adjustable. Lokar makes adjustable detent switches, also know as kick down kits; however this kit needs to be relocated from being gas pedal controlled to carburetor controlled. A better and more direct solution is that the transmission governor is adjustable. These adjustments can be made because the transmission governor is composed of weights and springs that are geared to the Trans output shaft. There are two outer (primary) and two inner (secondary) weights, and two springs. The inner, secondary, weights mainly affect full throttle 1-2 and 2-3 shifts. The outer, primary, weights mainly affect the part-throttle 1-2-3 shifts. If your shifts occur too soon you need lighter springs and/or smaller weights. If the shifts are too late, you need stiffer springs. B&M and TCI make governor recalibration kits. Transmission governor adjustments however will take a bit of trial and error to dial in.

(As a side note there are usually ink stamp numbers on transmission governors ranging from 11,13,15,17 etc., up to 23, 25 and 27. I do not know the correlation of these #s i.e. line pressure, spring tension, weights, rear gear ratio; but I do know that the higher the # the later automatic up-shifts will occur. A 25 or 27 stamp most likely had a 2.73 or 3.08 factory gear and an 11 or 13 stamp most likely came with a factory 4.56 or 4.11 gear.)

The third factor is load and speed and power, taking the above into account the valve body is internally calibrated to up-shift in a predetermined range based on a combination of engine load and speed. They are also designed to downshift when conditions require additional RPM to maintain vehicle speed or more commonly when we nail the fun pedal.

To gain total control of a Th400, installation of both a governor recalibration kit, a shift kit and some very light tinkering with the transmission vacuum modulator should do the trick.

[Luvlegs]

Whew... I'm going to have to study up some more. Like I mentioned earlier, I don't remember having any of this on my old car - I just remember bolting on the tranny, hooking up the speedo and off I went.
Does anyone have any links to good sites? (It'd cut down on me googling 'til my fingers bleed)... Thanks all for the information and if anyone has any pics of the "parts piles" for this stuff... I'd love to see it.