Turbo 400 kickdown problem
Thread Starter
Instructor
Joined: Nov 2013
Posts: 128
Likes: 29
From: Bloomfield Township Michigan
Turbo 400 kickdown problem
Hello all!
I am having a problem with the Turbo 400 kickdown in my '69. It doesn't. When I push the throttle down hard in 3rd gear it won't downshift to second. I know that this is and electrical function so I checked to see that the wire is plugged into the side of the transmission and it is. The trans shifts beautifully and has recently been gone through as part of an engine overhaul project and all is good. Any thoughts as to where to look next? I will check the switch under the accelerator pedal, and the connection at the fuse box. Any advise you can give me would be appreciated.
Jeff
I am having a problem with the Turbo 400 kickdown in my '69. It doesn't. When I push the throttle down hard in 3rd gear it won't downshift to second. I know that this is and electrical function so I checked to see that the wire is plugged into the side of the transmission and it is. The trans shifts beautifully and has recently been gone through as part of an engine overhaul project and all is good. Any thoughts as to where to look next? I will check the switch under the accelerator pedal, and the connection at the fuse box. Any advise you can give me would be appreciated.
Jeff
Pro
Joined: Apr 2013
Posts: 535
Likes: 8
From: London Ontario
Its likely an issue with the switch on the peddle. Sorry, you will have to become a contortionist or practice yoga, but, you will need to take a look up under the dash...
Check to make sure the connector on the switch is clean and fully connected. If it is, you can try adjusting it (yes they are adjustable).
Take a look at how it works when the peddle is pushed down. Push firmly on the end of the slide that comes out the rear of the switch (when you depress the peddle), push toward the engine. You should hear a slight click and the switch will push further forward than it was. Now just depress the gas peddle to the floor once and this will set the switch. Take it for a test drive and see if you have it working. If it still doesn't down shift you may need a new switch; the adjustment procedure is described in the replacement switch instructions.
Good luck!
Check to make sure the connector on the switch is clean and fully connected. If it is, you can try adjusting it (yes they are adjustable).
Take a look at how it works when the peddle is pushed down. Push firmly on the end of the slide that comes out the rear of the switch (when you depress the peddle), push toward the engine. You should hear a slight click and the switch will push further forward than it was. Now just depress the gas peddle to the floor once and this will set the switch. Take it for a test drive and see if you have it working. If it still doesn't down shift you may need a new switch; the adjustment procedure is described in the replacement switch instructions.
Good luck!
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
Have you verified that the kick-down switch is good at all by manually actuating the switch by hand and checking the other end of the wire at the transmission switch with the wire removed??? AND I assume you have checked for 12 volts also the kick-down switch.
I have also slid a section of rubber hose (3/8"id) on the plastic shaft of the kick-down switch and it then contacts the accelerator pedal when pressed...thus making it switch a bit sooner....if not operate correctly....as a 'quick test'...and then see if the switch can be adjusted or actually leave the rubber hose there and drive it. Also I have run into cars not allow it to switch due to floor mats under the pedal....and also on cars like yours where the accelerator pedal needs to be modified because when the accelerator pedal is pushed all the way to the floor....the carburetor is not being opened all the way on the primaries.
DUB
I have also slid a section of rubber hose (3/8"id) on the plastic shaft of the kick-down switch and it then contacts the accelerator pedal when pressed...thus making it switch a bit sooner....if not operate correctly....as a 'quick test'...and then see if the switch can be adjusted or actually leave the rubber hose there and drive it. Also I have run into cars not allow it to switch due to floor mats under the pedal....and also on cars like yours where the accelerator pedal needs to be modified because when the accelerator pedal is pushed all the way to the floor....the carburetor is not being opened all the way on the primaries.
DUB
Thread Starter
Instructor
Joined: Nov 2013
Posts: 128
Likes: 29
From: Bloomfield Township Michigan
Thanks to both of you for your responses. I know it is a tight fit under there as I have been there before. I will check the switch adjustment.
DUB- I like your idea of the rubber hose over the slide to quicken the kickdown. The accelerator linkage is working perfectly (the floor mat is not in the way) as the secondaries open as they should. I have checked the position of the throttle plates and this is good. I have not checked for 12 volts at the other end of the wire as you suggest and will do that as well.
Thanks again!
jeff
DUB- I like your idea of the rubber hose over the slide to quicken the kickdown. The accelerator linkage is working perfectly (the floor mat is not in the way) as the secondaries open as they should. I have checked the position of the throttle plates and this is good. I have not checked for 12 volts at the other end of the wire as you suggest and will do that as well.
Thanks again!
jeff
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
Inside the trans. pan there is a solenoid that can fail. It is of course hooked to the wire DUB mentioned. If you have voltage but no down shift the solenoid or a blockage of the solenoid gasket area is the next area to look at. I have seen auto. trans have problems due to lint from shop rags. A recent rebuild could have a small piece of foreign material blocking the solenoid port. Just what I have seen. Good luck with it. mike...
Thread Starter
Instructor
Joined: Nov 2013
Posts: 128
Likes: 29
From: Bloomfield Township Michigan
Problem solved!
Thanks all for your help. The accelerator lever was not touching the switch pin. The switch was adjusted as far as it could go. Something under there is obviously worn. I placed a narrow magnet on the lever and a piece of hose on the pin and now the transmission will drop into second just before the secondaries open or, if I push pedal a little further, it will downshift and the secondaries will open giving great acceleration. All is well. Thanks again!
Jeff
Jeff
Le Mans Master
Joined: May 2007
Posts: 5,028
Likes: 1,120
From: North tonawanda NY
Thanks all for your help. The accelerator lever was not touching the switch pin. The switch was adjusted as far as it could go. Something under there is obviously worn. I placed a narrow magnet on the lever and a piece of hose on the pin and now the transmission will drop into second just before the secondaries open or, if I push pedal a little further, it will downshift and the secondaries will open giving great acceleration. All is well. Thanks again!
Jeff
Jeff
Burning Brakes
Joined: Nov 2006
Posts: 893
Likes: 7
From: Orange Park Florida
You can actually hear the tranny kickdown (détente) switch operate. Key in ignition, turn key to acc position, depress accelerator to floor and have someone listen under the car tranny. This verifies switch operation.
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Thread Starter
Instructor
Joined: Nov 2013
Posts: 128
Likes: 29
From: Bloomfield Township Michigan
Jeff
Melting Slicks
Joined: Mar 2008
Posts: 2,023
Likes: 6
From: Austin Tx
After years of stomping the throttle linkage becomes bent.
https://www.corvetteforum.com/forums...kage-pics.html
https://www.corvetteforum.com/forums...kage-pics.html
Thread Starter
Instructor
Joined: Nov 2013
Posts: 128
Likes: 29
From: Bloomfield Township Michigan
I have verified that I am getting full throttle opening and the secondaries are opening fully as they are supposed to. Kickdown is working perfectly.
Jeff
Racer
Joined: Aug 2013
Posts: 480
Likes: 95
From: Georgetown Kentucky
I know this is an old post but just thought I'd add the instructions from the GM Service Manual for my '74, for the TH400 transmission kick-down switch, since the switch I purchased didn't come with any instructions. And yes it is a pain to change if you've never done it before ... much easier after knowing what's involved. I only had to remove the driver side AC duct.
The manual says: "After installing the switch, press the switch plunger
as far forward as possible. This presets the switch for adjustment. The switch will then adjust itself with the first wide open throttle application of the accelerator pedal."
When I pushed the switch plunger I could hear it clicking as I depressed it ... sort of like a ratcheting sound. I heard it click the first time I pumped the gas and it's working fine!
The manual says: "After installing the switch, press the switch plunger
as far forward as possible. This presets the switch for adjustment. The switch will then adjust itself with the first wide open throttle application of the accelerator pedal."
When I pushed the switch plunger I could hear it clicking as I depressed it ... sort of like a ratcheting sound. I heard it click the first time I pumped the gas and it's working fine!
