Technical Strange wiper problem

[JamieVoras]

I have a Fiat 124 Spider, 1978 U.S. version with an external mount motor and wiper mechanism. As long as the blades are not on the windshield, the wipers work great. If I remove the arms, the spindles move fine. If I snap the arms back so the blades are not on the windshield, they function just fine. As soon as you lay the blades on the windshield, they stop dead in their tracks. It has a brand new wiper motor, entire mechanism is properly lubricated and works freely. I went to a 10" blade, thinking that might make a difference, but none at all. It just stops dead in it's track. Everyone I've spoken with has been stumped! Any help will be greatly appreciated!