TH400 kick down response
Thread Starter
Intermediate
Joined: May 2009
Posts: 39
Likes: 0
From: Oshawa Ontario
TH400 kick down response
1970 454 auto. From a stand still automatic shifts predictably.
When cruising and give car heavy gas, kickdown does not respond very well. It does not want to downshift from 3-2 or 2-1.
I have check main items such as fluid level, modulator and TCS (transmission control spark) intake solenoid.
I checked these items in the sense that they appear to be connected correctly.
Looking for diagnostic advise
When cruising and give car heavy gas, kickdown does not respond very well. It does not want to downshift from 3-2 or 2-1.
I have check main items such as fluid level, modulator and TCS (transmission control spark) intake solenoid.
I checked these items in the sense that they appear to be connected correctly.
Looking for diagnostic advise
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The kickdown on your TH 400 is electric. The switch is inside the car mounted at the upper end of the accelerator pedal arm. Power should be on one side of the switch with the key on. When the pedal is nearly to the floor, the switch closes and sends power to the trans connector on the left side. Inside the pan (trans) there is a solenoid that causes the 3-2 downshift.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Now you need to see if the under-dash switch passes 12 vdc when activated, and if that voltage is received at the connection on the side of the tranny. If there is 12 vdc at the tranny when the kickdown switch is activated, the solenoid inside the tranny is defective or plugged up. They are easy to change out [if you can find a new one] once you drop the oil pan and remove the filter. It has an oval shaped coil cover, on a odd-shaped base, mounted to the bottom of the valve body with two small bolts. Good luck.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
The kickdown on your TH 400 is electric. The switch is inside the car mounted at the upper end of the accelerator pedal arm. Power should be on one side of the switch with the key on. When the pedal is nearly to the floor, the switch closes and sends power to the trans connector on the left side. Inside the pan (trans) there is a solenoid that causes the 3-2 downshift.
Thread Starter
Intermediate
Joined: May 2009
Posts: 39
Likes: 0
From: Oshawa Ontario
Thanks all! I will be looking into today. I just reviewed my factory service manual. Found the section for kickdown solenoid. It shows on the carb, beside throttle cable and adjustment instructions.
Thoughts
I'll let you know what I find
Thoughts
I'll let you know what I find
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Instructor
Joined: May 2008
Posts: 154
Likes: 3
From: Indiana
I have a 68 with a TH400. The switch is above the pedal and is yellowish plactic. It is activated by a lever at the end of the pedal.
If you have the same set-up on your 70 as I do on the 68, the switch can not be adjusted to my satisfaction. I have the switch adjusted as far as it will go and I still need to plant my foor to get it to downshift.
Would be interesting to see if anyone has a solution. I would like to have the kickdown work a lot sooner.
If you have the same set-up on your 70 as I do on the 68, the switch can not be adjusted to my satisfaction. I have the switch adjusted as far as it will go and I still need to plant my foor to get it to downshift.
Would be interesting to see if anyone has a solution. I would like to have the kickdown work a lot sooner.
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
I have a 68 with a TH400. The switch is above the pedal and is yellowish plactic. It is activated by a lever at the end of the pedal.
If you have the same set-up on your 70 as I do on the 68, the switch can not be adjusted to my satisfaction. I have the switch adjusted as far as it will go and I still need to plant my foor to get it to downshift.
Would be interesting to see if anyone has a solution. I would like to have the kickdown work a lot sooner.
If you have the same set-up on your 70 as I do on the 68, the switch can not be adjusted to my satisfaction. I have the switch adjusted as far as it will go and I still need to plant my foor to get it to downshift.
Would be interesting to see if anyone has a solution. I would like to have the kickdown work a lot sooner.
Have the same setup on my 73 and it is shiate! I think the objective at the time was WOT only. I have to shift down manually when I want on demand. I am considering trying this carb mount setup;http://www.jegs.com/p/B-M/B-M-TH-400...48054/10002/-1
Would love to know how adjustable it is...but appears that it would big improvement over the under pedal switch! I am going to order today.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
If you already have a functioning switch (even though it isn't adjusted to work properly), you just need some bits of hardware to create a shim or spacer so that it will activate sooner...or to re-position the switch so that it works. That stuff is available for pocket-change at your local hardware store. $50 to fix it is a bit much.... 
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
turn on the key
crawl under the dash
find the switch
push it by hand
if you hear a click in the tranny everything is working.
when i got mine it had a thick layer of electrical tape around it to make it kick down earlier.
crawl under the dash
find the switch
push it by hand
if you hear a click in the tranny everything is working.
when i got mine it had a thick layer of electrical tape around it to make it kick down earlier.
Instructor
Joined: May 2008
Posts: 154
Likes: 3
From: Indiana
If you already have a functioning switch (even though it isn't adjusted to work properly), you just need some bits of hardware to create a shim or spacer so that it will activate sooner...or to re-position the switch so that it works. That stuff is available for pocket-change at your local hardware store. $50 to fix it is a bit much....
Thread Starter
Intermediate
Joined: May 2009
Posts: 39
Likes: 0
From: Oshawa Ontario
Thanks: I like the idea of turning power on and pushing switch and listen for a click. That will be first. I may also shim or dowel. Is this a cronic problem for TH400? Are there any other components on the tranny that may also be causing problem?
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
If you already have a functioning switch (even though it isn't adjusted to work properly), you just need some bits of hardware to create a shim or spacer so that it will activate sooner...or to re-position the switch so that it works. That stuff is available for pocket-change at your local hardware store. $50 to fix it is a bit much....
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Okie-dokie. If it works for you, that's all that counts.
And, to the other poster: The kickdown solenoid is the only piece of cr@p in a THM-400. Early versions had a quality solenoid, but it cost too much and the GM purchasing boys found another one for less than half the cost. Of course, that one only worked half the time...or not at all. But since it wasn't a "safety" issue, no one cared [except for us owners, of course]. The rest of the tranny is bullet-proof. The tranny in my '71 coupe operates flawlessly and has never had an operational problem (per the 35 years of records in my possession)....oil and filter changes only. That's pretty d@mn amazing!
And, to the other poster: The kickdown solenoid is the only piece of cr@p in a THM-400. Early versions had a quality solenoid, but it cost too much and the GM purchasing boys found another one for less than half the cost. Of course, that one only worked half the time...or not at all. But since it wasn't a "safety" issue, no one cared [except for us owners, of course]. The rest of the tranny is bullet-proof. The tranny in my '71 coupe operates flawlessly and has never had an operational problem (per the 35 years of records in my possession)....oil and filter changes only. That's pretty d@mn amazing!
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
Sorry if I hijacked the thread surely didn't mean to. I surely agree with 7T1Vette on this from a basic operational perspective. I just wanted to point out that I have played with mine several times over the course of the last year and still can't get consistent ops, and it is definitely the switch. 
