Unfortunately his expertise is 1988 cars and on up, but he's been my family mechanic for years and gives me discounts & lets me pay big things in installments, etc.. and even though he doesn't really know much about the older cars he takes 'em to shops that do know and get opinions and suggestions from them.
He checked all the vacuum lines and that wasn't it so he's taking it to a classic car shop tomorrow.
I hope it just needs an adjustment like you said Bruce.
After this is fixed, you should find a transmission kickdown switch. These are common on all 68-79 big block (not Seville) Cads. I have a few; they need the correct carb linkage to engage. If that has changed, there are aftermarket kickdowns that can be adapted. Bruce
Automobile(s): 1969 Coupe DeVille, 1972 Sedan DeVille
Neptune Beach, FL
Re: Scary loud noises! Help!
With a kickdown switch, I think your trans should drop a gear when your put the pedal about 50% to the floor. (Don't quote me on the 50%, it's probably a different number.) If you are cruising in 2nd gear and put the pedal down to pass, and it doesn't drop into 1st, that would be the symptom of not having a kickdown switch properly installed/adjusted. Should also drop from 3rd to 2nd when you put the pedal to the metal. Mine had an arm-lever actuation. I discovered that the arm had fallen off the switch, found it laying on top of the intake manifold. Took me a while to figure out where it belonged. It was a big improvement once I figured it out and put it back together and adjusted it correctly. Like Bruce said, get one when you can - it's important for drive-ability/performance.