[Greg Reid]

'68 TH-400
The kickdown function hasn't worked on my car since I got it out of a 9 month stretch in paint prison. Worked fine before that. I installed carpet and thought that was the reason it wasn't working. I reset it according to what I know about that but it still does not work.

I believe downshift is a vacuum function at low speed and that would explain why it works ok at 20~30mph....it's just at 50 mph or so that I get nothing from it.

How do I check the switch electrically? Or is it shown in the shop manual?

[supercar]

The kickdown is an electrical switch located under the gas pedal. Check for 12 volts into the switch, and then depress the gas pedal and check for 12 volts out of the switch. Then check that the electrical hookup at the transmission is hooked at the connecter on the transmission. You could have a bad switch or no voltage. I hope this helps.

[Schurkey]

...or a failed kickdown solenoid in the transmission, or broken wiring anywhere in the system.

HOW did you adjust the switch?

It's not a bad plan to take the switch apart for cleaning and lubrication.
Switch shown is the later version, yours should be similar.

[wovenweb]

For those reading and since we are in the Street section, I think it is important to clarify that this is for A Body cars. '68 Firebirds used the carb mounted kickdown switch.

[steve25]

The A and B body cars!

[Greg Reid]

Thanks, the check for voltage was what I was wondering about. Didn't know if it was as simple as volts on the input, volts on the output..
Schurkey, I pushed the plunger all the way in and released, then I pushed the pedal to the floor. Not correct?
Thanks for the exploded view. I might tear it down and give it a good cleaning/lube.

[Ben M.]

Originally Posted by Greg Reid

Didn't know if it was as simple as volts on the input, volts on the output..

It's just an open and closed switch. Real simple. Other quick test is get underneath car on driver's side by transmission with key in Run, get a helper to push the pedal\switch so it closes and listen if you can hear the solenoid go "click" inside the transmission.

[Greg Reid]

Originally Posted by Ben M.

It's just an open and closed switch. Real simple. Other quick test is get underneath car on driver's side by transmission with key in Run, get a helper to push the pedal\switch so it closes and listen if you can hear the solenoid go "click" inside the transmission.

The 'click' is what I'd planned to check for if I didn't find a voltage problem. I went out to do this check this morning but somehow, the next thing I knew, I was on a riding mower.
Thanks for all the tips. I know I can track it down pretty easily now.

[Greg Reid]

Should be good now.
The switch is routing 12v through just as it should. The problem was that the pedal rod was not engaging the plunger far enough to activate the switch even after the adjustment. The mounting bracket itself seemed to be flexed rearward so that flooring the pedal barely engaged the plunger. Even with the two layers of gas line and heater hose (!) someone had pressed on it, the pedal was only moving the plunger maybe 1/8"...
I can only guess that it may have been from driving it without carpet (plus the heater hose) for a while.
Anyway, I flexed the mount back into a position where it makes easy contact (without the hose) and reset it.
I also took Schurkey's advice and 'overhauled' it. Using the trouble light, I'm getting activation at about 1/2 to 3/4 pedal.

[Schurkey]

Originally Posted by Greg Reid

Schurkey, I pushed the plunger all the way in and released, then I pushed the pedal to the floor. Not correct?

Nope. Well, maybe--depends on which direction you "pushed the plunger all the way" See below.

Originally Posted by Ben M.

It's just an open and closed switch. Real simple

Not exactly. They have a "ratcheting" self-adjustment feature. The switch will self adjust at first use, but only AFTER you set the initial position. See below.

Originally Posted by Greg Reid

Should be good now.
The switch is routing 12v through just as it should. The problem was that the pedal rod was not engaging the plunger far enough to activate the switch even after the adjustment. The mounting bracket itself seemed to be flexed rearward so that flooring the pedal barely engaged the plunger. Even with the two layers of gas line and heater hose (!) someone had pressed on it, the pedal was only moving the plunger maybe 1/8"...
I can only guess that it may have been from driving it without carpet (plus the heater hose) for a while.
Anyway, I flexed the mount back into a position where it makes easy contact (without the hose) and reset it.
I also took Schurkey's advice and 'overhauled' it. Using the trouble light, I'm getting activation at about 1/2 to 3/4 pedal.

I have seen and heard about folks wrapping the actuator pin with hose, which is SO dumb. The switch is self-adjusting but requires fifteen seconds of prep prior to the self-adjustment procedure. When you've done this once, you can do it "on the vehicle". (This applies to the later-style switch. Early switches are so rare around here that I've never held one in my hand.)

There is a spring tab on the slider assembly. Push it down, and shove the plunger all the way to the far end of it's travel. You'll hear the ratchet mechanism click.




Pull the plunger back so the spring tab engages again, mount the switch to the bracket...and depress the gas pedal so the carb goes to WFO. You'll hear the switch ratchet into correct adjustment.
You will, of course, have to verify that the gas pedal can open the throttle all the way.

Yes, the gas pedal is known to bend and not achieve true WFO, the throttle cables are known to fray and stretch and not achieve WFO, and the switch bracket bends so the switch isn't positioned properly, and idiots wrap hose around the actuator pin...all of this has to be checked and corrected as needed before the kickdown switch will work properly.

The switch should cause kickdown BEFORE you get to true WFO, yet still allow the additional pedal travel needed to fully open the throttle.

[Greg Reid]

For the sake of clarity, I'm going to define 'forward' as towards the front of the car and visa versa for this..and speak of the switch as it is positioned in the car.
With that, I did that wrong according to your last post Schurkey. My switch is as far forward as it can go while in the 'rest' position. Apparently my bracket is still bent rearward some. There is no locking tab to prevent the plunger from moving fully forward and as I say, it's in that position (fully forward) at rest.
As it's set now, it works at 3/4 throttle or so but does not come into contact with the pedal rod until I've pressed it an inch or so.
If I'm understanding your procedure, at rest (0 throttle) the pedal rod should be in contact with the switch plunger. Correct?
If anyone has a photograph of gas pedal mounting plate ON the car, I might get a better idea of the proper angle.

[Schurkey]

This is the later-style kickdown, from '70--'72. I robbed the switch, bracket, and gas pedal from a Treasure Yard car to install on my 'Camino.



Another person sent me a photo of the "correct" early-style switch and bracket that would be used on a '68 or '69. Note the difference in the position of the switch, and the bends in the gas pedal rod.



If Chevy is different from Pontiac, or Olds, or Buick "A" bodies in this regard, I don't know about it.

I'd love to have close-up photos of your switch, as they're so rare around here I've never seen a real one. If your trans kicks-down at something like 3/4 throttle and still has full travel to WFO, you aren't too far off. You could play with it a little to tailor the kickdown to suit your torque curve, or leave it as-is if it's dropping gear at an appropriate throttle position.

[Greg Reid]

Yeah, I may tweak it a bit but it'll work as is. Basically, it's like it's resetting to the initial setup point each time I release the accelerator pedal since it doesn't make contact until I start giving it the gas.
My switch is pretty much like the one shown in your El Camino photo. The 'catch' on mine is depressed so that it does not stop the plunger from moving forward. Because of that, it moves fully forward whenever it's at 'rest'.
I'll take a photo of it tomorrow and post it here.

[Greg Reid]

Actually, my switch seems to be in about the same position as the ones in your photos. If the locking tab was working on mine, it would not be resting fully forward but since it does not prevent the forward movement, it's at full forward travel.
Functionally, I don't see any difference in the operation?

[Greg Reid]

Here's mine. As you can see, the stop is not working so it goes basically to reset position whenever it's at rest....

[Schurkey]

If I understand you correctly, with the lock tab on the slider disabled, the ratchet shoe has been "adjusted" a million-billion times, so it is now worn-out and no longer holding position. The plastic "teeth" of the shoe are probably scrubbed off by the excess movement of the copper (or brass) contact.



FIRST thing to do is to return the lock tab on the slider to working position by bending it the minimum amount needed to make it functional. After that you could assess the ability of the switch to hold adjustment.

[Greg Reid]

The teeth are ok and even though the 'zip' sound is a little weak, there's still enough there to retain the ratcheting action as far as I could tell.
Since it doesn't require dis-assembly, I may pull it back out and 'reactivate' the locking tab if possible without breaking anything.
I have a pretty good junkyard around here that usually has a few GM '60s cars. I'll keep an eye out for a spare that may be in better condition.
Thanks for all the help guys.

[Mike O'Neill]

Thought I would resurrect this old thread rather than start a new one. Car is a 67 GTO, 400 and TH400. Engine is original, not sure about the trans.
Trying to figure out why I had no downshift, I found this thread and many others. Also found rubber hose and electrical tape on the switch. The patch had rotated so that the thick part was down. Rotating it up would give downshift, verified by road test. Bu this only works a short time before gravity rotates it back down.
So I removed the rubber hose, pushed the tab and pressed the slide all the way forward. But now, when I press the pedal all the way down, even with the floor mat out of the way and me pressing as hard as I can, the slide will only move about 1/8". I have to pull the slide almost the whole way out before I hear the solenoid click.
Nothing appears to be bent on the linkage. From the many threads I have read on the subject, it appears other have had this situation.
Would the switch be expected to activate with only 1/8" movement?

[Schurkey]

There's an "early" and a "late" gas-pedal mounted kickdown switch, with the change around 1969--70. Maybe you have the wrong one?

Gas pedal bent? Really common, but also interferes with getting WFO at the carb.

[Mike O'Neill]

Thanks for the quick reply.
I blocked the accelerator pedal down, and all 4 barrels of the Q-Jet were wide open.
The Ames catalog lists the same switch for 1967 - 1977 and it looks just like mine. Looks like my options are to either bend the switch mounting bracket, or rig up a more elegant variation of the rubber hose fix.
Here is another Rube G. fix:
https://www.gtoforum.com/f122/kick-d...57/index2.html
I suspect there has been variation in the pedal linkage geometry between manufacturing plants, or the rebuilder of my car changed the linkage somehow..