Thanks to suggestions from those on the list, I was able to put a new wiper arm on my '84 Fiero. As no one mentioned one critical step, and as I found a special tool unnecessary, I thought I'd tell how I replaced mine.
First step is to buy your new wiper arm. Inspection of it will likely make figuring out how to get the old one off obvious. I'd recommend a new one, rather than a junk one. It was just $30, and the splines on my old one were a bit chewed up. Before you do anything, get a slim 2 inch long (5 cm) nail or cut out a chunk of coat hanger wire. Pull the wiper ot scratch the paint. Put the wiper blade on the new arm, so you won't accidentally crack the windshield in case the wiper arm slips and smacks the windshield. The new wiper arm just popped on. To remove its "nail," push the end of nail while lifting the wiper on and off the windshield. Once the "nail" has moved a bit, enough of the head is free to grab with a pliers and pull all the way free.
My wiper now works great! It had never worked well in the five years I've had my Fiero. Sad part of the tale: I spent $30 on the new wiper, because I broke the old one trying to bend it so the blade would press more firmly against the glass (at highway speed the blade wasn't wiping at all! It would float above the glass.) After I got the new wiper I immediately saw the problem. The old wiper still had the "nail" in it! This didn't allow it to touch the glass, so apparently the previous owner bent the arm to get it to touch. Had I known that, all I would have had to do was to pull the "nail" out. Wish I had known that five years ago! It is possible the car came that way from the factory. So if your wipers aren't working as well as they should it would certainly pay to look and make sure your "nails" have been removed. From the top (side of the arm facing the top of the windshield, and near where it bends), the head looked like a rivet, but from the bottom (side of the arm facing the front bumper) you could see the end sticking out a little ways.
From: David Detienne