[cwcarpenter98]

Originally Posted by D'Monsta

Thanks for all this great info from all of you fellas.. My '66 GMC with 250 has an HEI distributor now. The original SM 318 is popping out of 3rd and vibrating to the point that the windows and heater diverter are rattling so loud I can't hear the radio!.. I have 2 of the SM-319 transmissions with OD so my plan is to clean one up real good, inside and out, and install it.. If it passes the 'gears good' test, I'll activate the OD functions.. Will post updates here..

Sounds like a good plan to me!





Update from Frankentruck:
Since I last posted on this thread, I was able to pick up a second overdrive transmission. That ended up being a good choice because not long after, the solenoid on the one in the truck started to fail. Swapped them out and haven't had any issues since.


No issues with the current wiring setup either.


There is one wiring thing that is not an issue for the overdrive, but I'm not fond of it when I'm not using overdrive. I prefer to drive around the small town of Milledgeville with the trans locked out of overdrive to take advantage of engine braking. Because of that, I added a toggle switch in the power wire that completely turns the power off to the system. The switch is on the power side, after the fuse, but before the main relay. That switch has worked great.
What I have noticed, and don't like, is that at all times, whenever the kickdown switch is hit, the ignition cuts. I can press the kickdown switch with my finger while the truck is idling and kill the engine. That also means that in lockout, if I want to go full throttle, I can't because I hit the kickdown switch and cut ignition.

I was thinking about adding an additional relay that keeps the circuit for the kickdown switch from actually doing its thing when I have the toggle switch mentioned above turned off. When I turn the power back on with said toggle switch, the additional relay will then allow the kickdown switch to do its thing when requested. That makes sense to me, so if I didn't explain it well enough, please tell me to explain my idea better

On the other hand, I'm curious as to why the kickdown switch does what it does when I don't have power to the system. Am I picking up power from the relay for the HEI that I haven't realized before? I don't know. I'm kinda lost on that one