Knock or thump from windsheild wipers

I have a 355 and this happened to me. Not sure if the wiper arm assembly is the same but on the driver side, there is a secondary arm just forward of the main arm and it has a cylindrical end to it that sits and rotates in a hole at the base near the main arm. This can pop out if the main wiper arm is lifted or has been removed at one time and not replaced in the proper position. It should rest straight across the glass parallel to the bottom of the windshield edge but mine was too far down so that when you lifted it to clean the windshield it would come into contact wtih the passenger-side wiper arm. When the secondary arm popped out during use, it would sound like a thump, very loud actually. Now that the wiper has been mounted correctly, it does not come out and no more sound.

 

By golly, Ben, I've got an answer for you! I use my wipers so rarely that I had never noticed the "knock" coming from them until I just tried it in the garage. First, I removed the wiper arms, just so that they would not be swiping over a dry windshield. Very easy, just pop off the caps and remove the 13mm nuts, but be very careful not to let the arms smack back into the glass while you are doing it. And be VERY VERY careful not to force the little pivot on the base of the pantograph arm on the drivers side. If you break it, a new wiper arm is about $400. Don't mess with it if you don't have some mechanical apptitude.

Once the arms were off, I turned on the wipers, and sure enough, knock, knock, knock. Where is that coming from?? It turned out to be easy to diagnose, the wiper linkage was hitting the little support tab that holds the trunk lining in place, in fact the linkage had worn a little notch into the tab. Just pull up the rubber seal at the left rear corner of the trunk opening, then lift up the corner of the trunk lining, and look towards the center, and you'll see just what this picture shows (with the famous "pool cue" which is really an arrow shaft). Just bend the tab up until it clears the linkage, button it all back up, and the noise should be gone!
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Nicely done Jeff, a fine example of what this site is all about.

 

Note that the wiper linkage is mounted directly onto the top of the pedal support housing, which may account for why you felt the "clunk" through the pedals.

To see if the little tab is hitting on your wiper linkage, you don't need to bother pulling the wiper arms off, just pull up the corner of the trunk liner and look in there. My point was to avoid running the wipers on a dry windshield and scratching it. Not good! If you just tilt out the wiper arms like you were cleaning the glass, then turn on the switch, you may run the risk of having them contact each other and bending or breaking something. You probably have a very simple problem, and we don't want it to turn into something bigger.

I'll be interested to hear what you find.

 

Gotta love the arrow shaft pool cue 348 diagnosis, Jeff!