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2008 Subaru Impreza hatchback with flopity back wiper

2008 Suburu Impreza hatchback with the little wiper on the back window. Being in Colorado, the little wiper gets a lot of work this time of year with ice/snow. Recently I started driving before clearing the back window all the way off (my bad) and turned on back wiper but it was frozen in place and didn’t move. No problem, just turned on the rear defroster and turned wiper off. About 10 minutes later (even though wiper was turned off), the wiper suddenly burst free. Cool, I thought. Except now, the wiper is out of sorts. That is, every time I turn it on, it will go part way across the window, but return off the edge of the window. Each time it goes back and forth it works its way further and further off the window until it’s pointing straight down and just flopping around.

I can move the wiper manually back to where it should be and sometimes it will stay in the right range for a few days, but will always return to the floppiness.

Is there a way to re-calibrate the range of the wiper to where it should be or is there something shot in the actual mechanism?

The wiper arm is probably splined on to the splined shaft from the motor. These splines are probably now stripped. If your lucky, the splines on the wiper arm are the only ones stripped. Then all you have to do is replace arm. But if shaft from motor is stripped, you probably have to replace motor, or fabricate a set screw or something.

Wipers are designed that if the wiper gets frozen to the glass, the splines on the arm will strip out instead of the splines on the motor shaft.

Replace the wiper arm.