Ok, (his son here), so my '76 is having some kinda issue, to start with what(not bad) it's an auto tranny, the shifting knob is loose, like I barely have to move it and I can get it in gear, but it won't stay in gear, it keeps popping out of gear, not slipping POPPING?? I don't know what is causing this, the tranny seems to be good. Please assist.
You will need to get under the car and physically check the condition of the components. Note what is sloppy/loose.Then determine what is necessary to correct the problem with the shift linkage.