I'm having problems with the sunvisors on my '70 SDV. They will flop part way down while driving. Sometimes over a big bump and constantly when I am driving with the windows down. It's kind of a nuisance when the passengers visor flips down, but when the drivers side flips right in front of my view while driving it is a bit unsafe. They will stay put if I put them forward against the windshield, but then my upwards view is restricted and it is hard to see stoplights. Does anyone have any tips or tricks to cure this problem?

My 65 Impala does this, too. I have found that you can get bushing rebuild kits that will fix it. Sorry - I don't have a link, but they're out there with a search...

Before there were goodies like bushing or other fix kits, I wrapped the shafts with aluminum foil to thicken it up.
That held the visors in place for a long time. (at least until I got rid of the car):shhh:

Don't forget to make sure the retaining screws are tight against the shaft. Sometimes just giving those a good twist will take care of the problem.

The ones on my '76 DeVille do this too, especially the passenger side one because it's got the mirror and vanity lights in it......

I forgot to mention that on my 65, I can prevent them from falling down by taking the ends out of the center catch and allowing the visor's weight to hold it in place on the shaft by friction.