I had a couple different suction cups. I had the one w/the pump & the red line painted on pump button. I had one that came w/Garmin StreetPilot. They would both lock so tight that you'd swear you would need a prybar to remove them.

The StreetPilot would drop off any windshield going down the road. The bigger one (had lightbar on it) would drop off at night.....always.

I tried glycerin. I tried window cleaner. I tried spit. Then I tried RAM mounts & that solved the problem. No more suction cups for me. I realize others make them work....but I'm happy to say I gave up. Ram mounts will not disappoint you.