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Discussion Starter · #1 ·
Hello....

I have a 70 l34 with idiot lights. but my problem is my th400 wont downshift when i stop or any other time. It shifts when i am running the shifter only. I have replaced the modulator and checked to see if the tcs relay works.... it switches. But i dont have my temp sensor in the head hooked up yet. Does this have to signal the tcs relay to send feed to the downshift solenoid? I am gettin kind of frustrated with this non shifting thing.
any help will be greatly appreciated.
jaze70ss
70 L34
67 427
 

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The TCS, Transmission Controlled Spark, has nothing to do with the shifting of the trans. It's function is to block or not block the vacuum advance to the distributor depending on engine temp and/or trans gear. The TH400 should have a switch on the throttle linkage that will cause the trans to down shift at full throttle. However If you trans is not downshifting when you stop I think it's a problem in the valve body, I'm not a trans expert so it's just a guess. What I can tell you is the problem is not associated with the TCS circuit.

I need to add this. The correct TH400 for the 70 will have two electrical connections, one for the TCS and the other is the downshift solenoid. If you have the TCS circuit connected to the downshift solenoid it will cause problems, not sure if it will cause the problems you describe.

Is this a factory installed TH400?

[This message has been edited by Elree Colby (edited 02-13-2003).]
 

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Discussion Starter · #3 ·
Thanks for the reply Elree... im pretty sure that the trans is the one that came with the car. the downshift soleniod was disconnected when i got the car. i just plugged it in. it is not connected to tcs. none of the schematics i have for the car even identify the orange wire to the solenoid. is it supposed to be constant like the other orange wires in gm cars?
 

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The orange wire is routed through the firewall to the throttle switch (TS). The other terminal on the TS has a pink wire that's from the IGN terminal on the fuse block (gets power when the ignition switch is on). The TS should close at or near full throttle sending power to the kick down solenoid.
 
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