Rear View Mirror Falls Off

[gator2511]

Cant get my inside rear view mirror to stay glued to the glass. I've done this many times before and it worked fine but this one has fallen off every time I glue it (within 24 hrs.). Used different glues and went by the instructions but it won't stick. I've ordered a 71 mirror and wondering if the inside cab metal is the same on a 71-72? I'm tired of playing with the glue and want to bolt it to the cab metal over the windshield.