1969 Deville Transmission Downshift Switch Confusion....

[Nick Liarakos #25230]

The TH400 in my 69 Deville convert upshifts flawlessly, but will not downshift in a "passing gear" scenario.  The downshift switch at the carb has 12V at it, but I am extremely confused as to how the carb linkage is supposed to actuate the switch itself.  The square shaft that extends from the carb side of the switch goes into a circular hole in the tab on the primary throttle shaft, but there is no way this engagement can rotate the switch to send 12V to the solenoid in the trans.  I am missing a part or parts, likely thanks to the shop that did the top end engine work before I got the car.

The service manual goes into detail on the procedure on pages 6-69 and 6-70 and based on the description it would seem I am missing a lever and a torsion spring of some kind.  Without photos, I cannot be sure though. 

Will photograph this tomorrow when I have access to a camera and perhaps someone can tell me what I am missing.

[bcroe]

All my 70s engines have a switch with a plastic arm engaging the carb linkage.  Could that arm be broken off, or is 69 just different?  Bruce Roe CLC # 14630

[Nick Liarakos #25230]

Bruce,

Thanks for the reply.  Even though the 69 manual is extremely comprenesive, there is no photo of the part I'm missing.  I believe it is a combination of lever that mounts to the switch and a rotary spring.  I believe I've sourced a replacement.  Once I put it together I will post a photo to this thread in the event that someone else comes across the same issue, they can search the forum archives and find this.

[CaddyShackPA]

Yes, the 69 has a flat(tish) metal crank arm that slips over the square shaft on the switch and rides against the throttle linkage pin. The round hole on the linkage arm just makes room for the square switch shaft, it doesn't engage it in any way.

Unless my 69 is missing something, the switch arm is retained on the switch only by the torsion spring, so in your case it may have gone flying when someone disassembled it and it was never replaced.

Use care when winding the required one turn of tension into the torsion spring; this can involve some digital dexterity to avoid planting the spring wire into your finger. Consider gloves. And safety glasses. And possibly a helmet.