So my 1994 Chevy Lumina APV minivan's rear wiper has been... stiff for some time. If I pull it away from the window, it stays pulled away. It will do one wipe from bottom to top, but on the return stroke it stays clear of the glass. Not an optimum situation to say the least!
It's definitely corroded. Looking at the hinge, where the rivet passes through from top to bottom (as installed) I can clearly see the oxidation built up. I tried penetrating spray, but it only got a teeny bit freer, nothing like it is supposed to act.
I looked at it for a bit but could not figure out how to pull the wiper arm off the shaft. After looking at
WikiAnswers for a bit, I came across a post that made the Aha! light come on. There's a clip that's part of the arm (it does
NOT come off) that you can slide out of the way.
This is a photo from the bottom (as installed) of the wiper arm. See that little tab sticking down? That's part of the clip that you can use to pull the clip out of the was,
but wait a second! Get a large, flat screwdriver. Pull the wiper arm as far away from the window as it will go. This is important - there is an intentional 'lock' that holds the clip in when the wiper blade is pressed against the window.
Now that the arm is pulled away from the glass, pry the tab against the bottom of the wiper arm and pull the clip down as far as it will go. It isn't much; maybe a quarter of an inch. A pair of needle nose pliers might help, but I didn't need them.
This is what it looks like with the clip all the way down. The wiper arm is ready to remove from the wiper motor shaft.
Once that clip is down, the arm should pull straight off the shaft. It's splined, and not attached in any way other than a friction fit on the matching splines on the shaft. Mine came off with some
gentle rocking ans a teeny bit of prying with the large screwdriver backed with some wood scraps against the rear door. If you squeeze the arm against the shaft (like with a pair of vise grips) you'll probably never get it off. If you become desperate, get a Dremel-style tool and cut a slit in the base of the wiper arm opposite the arm. You'll need a new wiper arm, but the motor shaft will be intact.
This is what the arm looks like once it's been removed. Note the way the clip slides behind the motor shaft. As for the obvious damage (all the gouges and scratches) those came from me trying to wiggle the frozen, corroded joint by holding the end with pliers and wiggling the arm.
Not a good plan.
In order to loosen that up, I used a wire brush to remove a bunch of corrosion, a soak in penetrating oil and then held the end (this time with some paper towel to protect the remaining splines) and wiggled some more. No good.
I used a small flat screwdriver to scrape away all the corrosion I could from the area with the arm in it's 'away from the glass' position, and also by moving the clip back and scraping when the arm is in it's 'against the glass' position. That helped some, as did squirting some graphite powder all round the area.
Ultimately, I decided I had nothing to lose, and so with the hole facing down, I drove a tiny screwdriver into the hinge area to open up the space between the arm and the 'socket.' That worked! I don't know for how long, but I dumped more graphite into the area, worked it back and forth and was satisfied enough to put it back. Before replacing it, I put some general purpose machine oil on the motor splines. Hopefully, if I have to get it off again, it'll come easy!
In the style of the Mythbusters, I set out to determine if the myth that children prefer the box to the present contained therein. I'm pleased to report that with a sample size of one, the myth is plausible.
It's my brother, Lee! He surprised me by just dropping by on a whirlwind tour of the family here in the 'states. His daughter is on her way to university in Hawaii. How exotic is that?
This is a photo from the bottom (as installed) of the wiper arm. See that little tab sticking down? That's part of the clip that you can use to pull the clip out of the was, but wait a second! 
This is what it looks like with the clip all the way down. The wiper arm is ready to remove from the wiper motor shaft.
This is what the arm looks like once it's been removed. Note the way the clip slides behind the motor shaft. As for the obvious damage (all the gouges and scratches) those came from me trying to wiggle the frozen, corroded joint by holding the end with pliers and wiggling the arm.
