400 kickdown - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**53burb** · 09-10-2005, 01:08 PM

I have a recently rebuilt 400 tranny w/o the kickdown hooked up. When I bought the Burb, it wasn't installed, and I had the tranny rebuilt a few months ago. According to what I have read here, the tranny should still kickdown into 2nd gear w/o the kickdown installed & down into 1st with it installed.Well mine doesn't kick down into 2nd gear. Is there something wrong with the tranny that I need to have the shop look at??? It didn't
kick down before the rebuild either.

GMan69 · 09-10-2005, 08:03 PM

Mine will kick down at slower speeds, such as turning a corner. One of these days, I might actually hook the darn thing up.

JimKshortstep4x4 · 09-10-2005, 08:37 PM

The TH 400 should kick down under partial throttle, (slow speeds) without the detent switch hooked up. Two possible causes of your transmission not down shifting at slow speeds are: 1) modulator valve, 2) control valve. (Of course it is important that the vacuum line is hooked up to a good vacuum source on the engine).

I think that the modulator valve would be the most likely problem since you have had the transmission rebuilt. If you cannot get it to downshift after changing out the moulator valve, I would suggest taking it back to the rebuilders.

Jim

**53burb** · 09-11-2005, 12:54 AM

I am pretty sure the modulator was replaced during the rebuild, but I will definately look at it tomorrow. Is there a way to test it??? How exactly or at what throttle or RPM should the tranny kick down?? Where is the control valve?? The vacuuum is hooked up in the typical place, behind the carb on the intake manifold (full vacuum).

*Javy* · 09-11-2005, 03:09 AM

Hello,
The good thing about this 400 trans is that you don't need
a mechanical linkage for the the kick down.It is electronic.
I mounted a micro switch under my gas pedal to activate
"passing gear and NOS".Very simple.You don't need NOS for
your passing gear to work,just the switch.

chevyguy_72 · 09-11-2005, 09:03 AM

Quote:

Originally Posted by Javy

Hello,
The good thing about this 400 trans is that you don't need
a mechanical linkage for the the kick down.It is electronic.
I mounted a micro switch under my gas pedal to activate
"passing gear and NOS".Very simple.You don't need NOS for
your passing gear to work,just the switch.

Do you have any pics? maybe a write up?

JimKshortstep4x4 · 09-12-2005, 06:00 AM

53Burb,

The control valve is the main transmission control with all the springs, spools, and balls in it. It is located on the bottom of the transmission and is accessed by removing the pan.

The modulator can be checked for leaks and whether it moves or not when vacuum is applied. If it has been replaced recently then it almost rules out the vacuum modulator as the problem. I was not able to find a mph on when the transmission downshifts.

Whoever overhauled the tranny should be contacted. Working on the valve body can lead to other problems if not done correctly.

Jim

**53burb** · 09-12-2005, 08:22 PM

My modulator was replaced. Any suggestions as to what I should tell the tranny shop?? I printed out this post to show them this. When should the tranny kickdown??

skokie · 09-12-2005, 11:24 PM

You should be getting whats called a governor kickdown. Take it to the tranny shop, tell them whats going on and let them test drive it. Could be something as simple as a vac mod, bad governor or it could be something bad like the valve body. Keep us posted on what you find out..

**53burb** · 09-13-2005, 01:24 PM

I was talking with a friend about this problem. My truck will shift up and down fine when initially taking off or slowing down. It just won't kick down if you stomp on the gas if you just want to get on it or pass someone. I guess I do need the electric kickdown hooked up for this. I am going to feel real stupid if this is correct.

69 longhorn · 09-13-2005, 03:24 PM

Quote:

Originally Posted by 53burb

I was talking with a friend about this problem. My truck will shift up and down fine when initially taking off or slowing down. It just won't kick down if you stomp on the gas if you just want to get on it or pass someone. I guess I do need the electric kickdown hooked up for this. I am going to feel real stupid if this is correct.

No, you dont need the elect kick down switch for the 3 to 2 kick down. The only function the elect provides is a 3 to 1 kick down (under 35mph). my bet is that you have a sticky valve in the control assy......I had a prob with mine , & it straightened up after some run time. You might run it by your trans builder tho..... crazyL

**53burb** · 09-13-2005, 04:02 PM

Not to drag this on, but if I step on it then it then it should kick down into 2nd if I am over 35mph, but if I have the electric kickdown hooked up, it would kickdown to 1st below 35??? Correct????

69 longhorn · 09-13-2005, 04:11 PM

Yup

**53burb** · 09-13-2005, 04:51 PM

Thanks, you guys have been a big help!!! I will reply back to this post when I have an update, might be a few weeks before I get it loooked at.

09-10-2005, 01:08 PM	#1
53burb Senior Member Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,010	400 kickdown I have a recently rebuilt 400 tranny w/o the kickdown hooked up. When I bought the Burb, it wasn't installed, and I had the tranny rebuilt a few months ago. According to what I have read here, the tranny should still kickdown into 2nd gear w/o the kickdown installed & down into 1st with it installed.Well mine doesn't kick down into 2nd gear. Is there something wrong with the tranny that I need to have the shop look at??? It didn't kick down before the rebuild either.

09-10-2005, 08:03 PM	#2
GMan69 Registered User Join Date: Mar 2001 Location: Hernando, MS USA Posts: 1,152	Mine will kick down at slower speeds, such as turning a corner. One of these days, I might actually hook the darn thing up. __________________ George Morgan Hernando, MS '69 C-10 swb fleetside '72 GMC swb Stepside Last edited by GMan69; 09-10-2005 at 08:04 PM. Reason: correction

09-12-2005, 11:24 PM	#9
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	You should be getting whats called a governor kickdown. Take it to the tranny shop, tell them whats going on and let them test drive it. Could be something as simple as a vac mod, bad governor or it could be something bad like the valve body. Keep us posted on what you find out.. __________________ RIP to my son Dylan. 5/17/2002 - 8/18/2018 If you want to know more about rare forms of pediatric cancer or if you want to help fund pediatric cancer research, please check out the website for the non-profit I started. https://slothforpedcancer.org 68 build thread http://67-72chevytrucks.com/vboard/s...d.php?t=223234

09-13-2005, 04:11 PM	#13
69 longhorn Registered User Join Date: Aug 2001 Location: rock island,il,usa Posts: 5,382	Yup __________________ http://community.webshots.com/user/hotrodhorn

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09-10-2005, 08:37 PM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	The TH 400 should kick down under partial throttle, (slow speeds) without the detent switch hooked up. Two possible causes of your transmission not down shifting at slow speeds are: 1) modulator valve, 2) control valve. (Of course it is important that the vacuum line is hooked up to a good vacuum source on the engine). I think that the modulator valve would be the most likely problem since you have had the transmission rebuilt. If you cannot get it to downshift after changing out the moulator valve, I would suggest taking it back to the rebuilders. Jim

09-11-2005, 12:54 AM	#4
53burb Senior Member Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,010	I am pretty sure the modulator was replaced during the rebuild, but I will definately look at it tomorrow. Is there a way to test it??? How exactly or at what throttle or RPM should the tranny kick down?? Where is the control valve?? The vacuuum is hooked up in the typical place, behind the carb on the intake manifold (full vacuum).

09-11-2005, 03:09 AM	#5
Javy Account Suspended Join Date: Jan 2004 Posts: 129	Hello, The good thing about this 400 trans is that you don't need a mechanical linkage for the the kick down.It is electronic. I mounted a micro switch under my gas pedal to activate "passing gear and NOS".Very simple.You don't need NOS for your passing gear to work,just the switch.

09-12-2005, 06:00 AM	#7
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	53Burb, The control valve is the main transmission control with all the springs, spools, and balls in it. It is located on the bottom of the transmission and is accessed by removing the pan. The modulator can be checked for leaks and whether it moves or not when vacuum is applied. If it has been replaced recently then it almost rules out the vacuum modulator as the problem. I was not able to find a mph on when the transmission downshifts. Whoever overhauled the tranny should be contacted. Working on the valve body can lead to other problems if not done correctly. Jim

09-12-2005, 08:22 PM	#8
53burb Senior Member Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,010	My modulator was replaced. Any suggestions as to what I should tell the tranny shop?? I printed out this post to show them this. When should the tranny kickdown??

09-13-2005, 01:24 PM	#10
53burb Senior Member Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,010	I was talking with a friend about this problem. My truck will shift up and down fine when initially taking off or slowing down. It just won't kick down if you stomp on the gas if you just want to get on it or pass someone. I guess I do need the electric kickdown hooked up for this. I am going to feel real stupid if this is correct.

09-13-2005, 04:02 PM	#12
53burb Senior Member Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,010	Not to drag this on, but if I step on it then it then it should kick down into 2nd if I am over 35mph, but if I have the electric kickdown hooked up, it would kickdown to 1st below 35??? Correct????

09-13-2005, 04:51 PM	#14
53burb Senior Member Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,010	Thanks, you guys have been a big help!!! I will reply back to this post when I have an update, might be a few weeks before I get it loooked at.



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