TH400 Setup Questions

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Supercharged111

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Oct 25, 2019
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I'm TH400 ignorant. My old C6 had an easy to set up kickdown rod, my 700R4 had an easy to set up TV cable, but the 400 on my Monte doesn't shift right and I suspect it's a setup issue because when this power train was in the motorhome donor it acted normal. I know there's a vacuum modulator on this trans, but I can see the line is hooked up. What else should I be looking at? I should point out that I didn't do the swap nor was I present for it.
 

84GP455

G-Body Guru
Jun 19, 2007
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Methuen Ma.
I've had a TH400 in my 84GP for about 25 years with little to no problems at all. I switched to the TH200-4R a few years ago and love it. In my opinion a kick down rod and a TV cable is more trouble to hook up and get it right than the TH400 vacuum control module. If you can see the vacuum line is hooked up from the module to a port on your carb then you are missing the kick down switch which is connected to the gas pedal bracket and is wired to the fuse box. I'm not sure what year your Monte is but, I don't think they came stock with the TH400 unless it is a 70's model. This is the switch that you need
https://www.summitracing.com/parts/...MIq8X7gcvF5QIVkoCfCh3sSQr6EAQYBSABEgKkJfD_BwE
and the bracket for the gas pedal is from any 70's TH400 car, then you just wire it up to the switch on the transmission.
kd01.jpg
 
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Supercharged111

Comic Book Super Hero
Oct 25, 2019
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Colorado Springs, CO
Easy peasy bolt in goodness on the kickdown switch? I neglected to mention that the upshifts are what are being weird. You have to rap the thing out to get it to upshift. Do I need a new modulator or are they adjustable? My dad may have done some weird sh*t to it, he was very convinced it was more of a race car than it is.
 

84GP455

G-Body Guru
Jun 19, 2007
779
95
28
Methuen Ma.
The switch is easy to mount but you need to get the correct bracket, That motor home should have it if it's still available. I went to the junkyard and got a gas pedal from a "B" body 70's car and it bolts right up in place of the 80's bracket. There is a mounting spot on the bracket for the switch. The transmission should upshift with the module but it won't kick down to a lower gear when you mash the pedal, that's what the switch does, it will just bog in whatever gear that you're in. They do make adjustable vacuum modulators for the TH400, that's what i had on mine, take the vacuum line of the modulator and get a long skinny flat head screw driver and stick it in the hole and try to feel for a screw, that's what adjusts the shift points. In will hold the transmission in gear longer and screwing it out will make the transmission shift sooner. If I remember correctly, it's been a while. Usually the smaller aftermarket modules are the ones that are adjustable. The big bulky modules are the factory ones and they are not adjustable. I used an adjustable one from B&M for the TH350 because it's smaller and gives more room for headers.
 

Supercharged111

Comic Book Super Hero
Oct 25, 2019
4,908
7,670
113
Colorado Springs, CO
So those are the only 2 things that externally control the shifts on a 400? I haven't driven the car enough to see the downshifts, I assume they don't exist. For all I know this car was originally a V6 car, but unfortunately the motorhome is long gone. Luckily old cars survive here in CO so shouldn't be the end of the world to grab that kickdown switch.
 

mikester

Comic Book Super Hero
Mar 10, 2010
2,904
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Small town NY
I've had a TH400 in my 84GP for about 25 years with little to no problems at all. I switched to the TH200-4R a few years ago and love it. In my opinion a kick down rod and a TV cable is more trouble to hook up and get it right than the TH400 vacuum control module. If you can see the vacuum line is hooked up from the module to a port on your carb then you are missing the kick down switch which is connected to the gas pedal bracket and is wired to the fuse box. I'm not sure what year your Monte is but, I don't think they came stock with the TH400 unless it is a 70's model. This is the switch that you need
https://www.summitracing.com/parts/...MIq8X7gcvF5QIVkoCfCh3sSQr6EAQYBSABEgKkJfD_BwE
and the bracket for the gas pedal is from any 70's TH400 car, then you just wire it up to the switch on the transmission.
View attachment 127218

I have a thread about TH400 kickdown switch. I guess you didnt see it. Im in the same mess. I need this bracket. Do you think it might be the same bracket in an early van or pick up ? Not that many 70s cars left in the yards out here. Finding this might be tough.
 

mikester

Comic Book Super Hero
Mar 10, 2010
2,904
3,641
113
Small town NY
I've had a TH400 in my 84GP for about 25 years with little to no problems at all. I switched to the TH200-4R a few years ago and love it. In my opinion a kick down rod and a TV cable is more trouble to hook up and get it right than the TH400 vacuum control module. If you can see the vacuum line is hooked up from the module to a port on your carb then you are missing the kick down switch which is connected to the gas pedal bracket and is wired to the fuse box. I'm not sure what year your Monte is but, I don't think they came stock with the TH400 unless it is a 70's model. This is the switch that you need
https://www.summitracing.com/parts/...MIq8X7gcvF5QIVkoCfCh3sSQr6EAQYBSABEgKkJfD_BwE
and the bracket for the gas pedal is from any 70's TH400 car, then you just wire it up to the switch on the transmission.
View attachment 127218

So after about an hour and a half of searching through countless cars, vans and trucks I came home with 3 brackets similar to whats in that photo. Not exactly like that but similar. One came out of a 76-77 El Camino. Another one from a C-20 van and the last out of a pickup. Im not sure which one if any will work. I need to clean them all up a little before I try them. Funny thing is not one of them still had a switch.
 
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