I do not know, really, if Frank ever changed his tune. While I heard him toy around with some Elvis material, it was the tame stuff. Frank, even though he had a number of popular songs during the rock era, stuck to his roots. He did it his way, so to speak, and did not rock out.
1966 was a wonderful year for the Sinatras. Frank's daughter Nancy had a #1 rock n' pop hit. Her dad had, previously, had #1 songs but not during the rock era. I do not know how daddy Frank felt about Nancy's #1 rock tune, but she sure got more than her share of the attention with this smash.
Nancy's song hit big in February. Then, and this was quite amazing, Frank himself went all the way to #1 only six months later. "Strangers in the Night" was competing with all the top rock performers of the day -- Beatles, Stones, Beach boys, etc -- but Frank had the clout and talent to take a classy middle-of-the-road song all the way to the top of the charts.
As a side note, 1967 was not such a bad year for the Sinatras either. Come April they were back at the top of the charts -- together. Dad and Nancy had teamed up to record "Something Stupid" and it was #1 for four weeks. Figures, but I could not find a video of Frank Sr performing this song with Nancy. However, for some reason, Frank Jr sat in for dad on The Smothers Brothers TV show. I wonder if dad was trying to promote son's career? Anyway, this is kind of interesting for what it is, and the hit song is featured here even if there is a substitute Sinatra. Jr, at that time, did look much like a younger version of his dad. His sound was similar as well.
For more "Stories Behind the Music" click on the guitar 
Steven L. Smith
Bellingham WA Home Inspections
Check out "This Day In History" -- music and vintage television from the 1950's through the 1980's. I enjoy writing these articles because they take me back to my days in radio broadcasting. Click on Elvis' gold record, below, to revisit those golden hits of yesteryear.
Steven: I was always a fan of Frank Sinatra... and my mother adored him. Nancy was cute... and it's nice to see those young ladies behind her in the video doing the "mashed potatoes." Thanks for sharing.
The boots video had to be one of the most provocative, don't understand why I don't remember that one. Wasn't a big Nancy S. fan.
Jack,
I did not knowingly post something that would turn you on.
Steven, I absolutely could not stand Nancy Sinatra's singing or her songs. That "Something Stupid" song really was stupid. I just recently bought a 1950's Grundig console stereo h-fi and now can listen to Frank Sr. the way he was meant to be listened to, 33 RPM High Fidelity! Oh and of course Tony Bennett, Benny Goodman, Glenn Miller, Perry Como, and all the other great artists. Funny thing is, all my 60's albums don't sound so good on that machine :-)