1992 pickup with intermittent wipers, what determines the travel limits of wiper blades? Most of the time the blades go too far down and off the glass tearing up the rubber wiper. The "up sweep" travel is ok. I detect some play in arms, maybe inch or so.
Could it be a motor or relay issue?

 

sounds like you just need to pull the wiper arms and turn them a couple splines

 

My 87, driver's side, either hits up top or down below. The splines aren't "fine" enough to get it not to hit. No adjustment on the motor that I could find in the FSM. As Blake said find the fit that works best.

 

Like Blake says^^^

 

OK thanks I'll try that, but what causes the play or looseness in arms? I checked it again and there is more like 3.5 inches play up/down in both arms simultaneous. I've not fooled with wiper motor yet but suspect linkage is loose somehow.

 

3 inches play? Must be something wrong mechanically. Could be stripped splines. You are in the best position to find out. Feel it.

 

Found that the transmission bushing closest to wiper motor is worn out, searches indicate no longer available. Will try to improvise as others have done.

 

Good job! I'm going to take a closer look at mine.

 

I just shimmed it up with a couple plastic washers I cut from a bucket lid. Took almost all of the play out of it and didn't have to remove the assembly ,done it through the motor hole.