Acme threads?
Do you mean the square bottom spiral threads/grooves inside the base that allow you to change the height by rotating the motor? The 75182 is the model designation for the motor itself.
You may have got one of the pins on the motor out of the groove. The grooves are about 1/4" wide, the pins re about 1/16" in diameter, small enough to easily slide in them. They may be off set to one another to take up the difference, I donno?
I don't thing spreading the clamp open too far will help, it may crack the base.. You just need to see which way the motor need to be bumped back into position by placing it on a flat surface and looking for the tilt in the angle of the motor. You can try to "man-handle" it back into the grooves or maybe a sharp rap with a plastic mallet.
I looked at my motor and base and I can't imagine what it must have taken to get it wedged in place. I will take a photo if that will help. It may just be "stuck" rather than out of the groove. You might try tightening the clamp to see if that will snap it back into position. Sometimes there's only 2 things you can do and sometimes it's the opposite of the logical one to try next ...I donno? :blink:
There may be only one way to start the motor into the base because of the pin orientation. You may have started it in the wrong position... again I'd have to check.
I'll post back.