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Discussion Starter · #1 ·
Long standing issues with a non-op TH400 kickdown switch (the one on the gas pedal assembly).

Already replaced the assumed faulty original switch with a new one when I had my old TH400 in
Then I replaced the transmision with a new TH400

Thought that between those 2 things I'd have a functioning kickdown. I've tested the switch "manually" by engaging it with my hand while driving. Nothing, so the issue is not with mounting.

Likely not the switch itself (replaced) or the electric solenoid in the trans (low odds of 2 units being both bad in 2 transmissions).

It is a simple 2 wire system (right?) where the switch completes the circuit. The wire from the switch to the trans is fine. The other wire to the power source at the panel looks fine. The harness connector looks fine.

So what do I check next?
 

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Discussion Starter · #3 ·
I have had a bad switch right out of the repop box. Took it apart to find it missing some guts that would make it function. Second one sent was fine.

You can bench test the switch with a multi meter (on continuity setting) or a battery, jumper wires, & and test light.

Make sure you are getting power to the switch from your wiring harness. If so, you could check for power on the switch terminal going to the transmission when the switch plunger is activated. This test would take the place of the multimeter or test light bench test. Note: these switches are self adjusting, but they have to be set up upon installation to self-adjust, I think.

There is a down shift solenoid in the transmission that could be bad. IIRC it is grounded inside the transmission by a short wire if it is a one wire solenoid. Solenoid could be bad or not grounded.
Thanks man. I seriously doubt that 2 switches and 2 solenoids are bad, but who knows!

I suspect an issue in wire continuity and will test the circuit at the solenoid.

Several folks have told me these are "self adjusting" but I cannot for the life of me see how that can be. it just screws the the pedal brace and slides back to engage the circuit when the pedal is to the metal. I usually put a piece of vacuum tube on the switch shaft to make it engage quicker, but know of no other adjustment than that. Please LMK if I'm wrong!
 

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Discussion Starter · #7 ·
Not sure my switch is the same one in the diagram.

The one in the diagram looks like a switch box with a shaft that moves back and forth in it. You appear to push it all the way forward (toward the engine), then use the gas pedal to "set" activation depth when pished all the way down. I get that.

My switch is sliding switch with a shaft that protrudes perpendicularly from the switch that engages the pedal. There is no adjutability to it. Here is the thread for the one I bought and installed:


do I have the wrong switch? Or am I somehow botching this simple procedure
 

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Discussion Starter · #22 ·
Thanks guys, for all the info.

Some clarifications:

1. I have to assume the car has the '66 pedal assembly bracketry, but not sure
2. the system once worked! my OLD trans was a '69 TH400 (PX-69-34722). Kickdown used to work on this trans, then stopped. I replaced the switch with the new referenced one while this trans was still in car. No workey.
3. I replaced the old kickdown switch with an identical new switch for TH400s.
4. I replaced the entire TH400 last month with a known fully functioning (including solenoid) TCI Streetfighter trans (later model case with metric bolts). Trans works great, but still no kickdown.
5. single terminal solenoid on old and current trans. Solenoid confirmed hooked up (verified this when I changed the pan)

Writing all this out makes me thing something is amiss in the wiring, so I guess I'll have to go down the test light road. :(
 
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