This Is Fascinating! How Windshield Wiper System Works | Transmission Linkage, Motor, Arm & Blade
The way windshield wiper works is actually very fascinating. You may not realize this, but there’s an elaborate linkage just below the base of your windshield that allows your car’s wipers to move back and forth and, in some cases, up and down—and it is fascinating.
In this video, young mechanic Aiman will show exactly just that. We’ll let the video do most of the talking, but the idea behind how wiper arms move back and forth deals with using pin joints, linkages and bellcranks to restrict certain degrees of freedom, and allow motion only where you want it.
This is Part 4 in the series of videos on How To Remove, Replace & Install Windshield Wiper components such as the transmission linkage, the motor and the arm. Also DIY repair & ideas on how to fix the stripped spline on the steel shaft of the linkage arm, which we will discuss more below:
Part 1: (Removal of the Linkage Assembly - This video)
Part 2: (Re-install of Transmission Linkage Assembly & Cowl)
If you think windshield wipers consist of just boring metal arm shoved at the end of electric motors, you couldn’t be more wrong! Wiper arms are controlled by “wiper transmissions,” intricate linkages that translate the unidirectional rotation of a motor into back and forth motion of wiper arms, which have rubber blades attached to them to clean water and grime from your windscreen.
The primary mechanism for any wiper transmission is an electric motor whose output shaft is a worm gear. That worm gear spins a ring gear seen in the picture above (this gear-mesh multiplies the motor’s torque), which sits on a shaft that goes through the bottom of the casing.
That shaft has a small metal link bolted to it, so as the motor’s worm gear spins the ring gear, the latter’s shaft actually rotates the link like a propeller blade on an airplane engine.
At the end of that “propeller” is a rod attached to a pin or revolute joint; that One Degree Of Freedom-joint restricts translation of that rod in any direction relative to the attachment at the end of the link, but allows for rotation about a single axis. What this means is that as the ring gear shaft spins its link, that pushes and pulls the rod, but because that link is free to rotate about its joint, the other end of the rod does not necessarily have to move up and down as the ring gear link rotates—it can just move left and right.
It’s a bit hard to visualize, which is why we have that video, but the main point is that, by restricting certain degrees of freedom, and allowing for others, you can translate unidirectional rotation into translation of wiper arms.
What led us to do this video is that we've stripped the teeth / splines (the steel shaft stud where the arm socket goes into) off of our windshield wiper arm and the bolt it attaches to therefore the wiper arm no longer working properly (The wiper arm is generally aluminum, the wiper stud is steel).
We did a video to explain why the stud teeth may have stripped. Here's that video:
Dorman do sell plastic bushings to temporarily fix this problem (you can buy them at Advanced Auto Parts), but a permanent solution would be to replace the entire linkage assembly. Since the used part (the whole transmission linkage including the motor) is cheap enough, we've decided to replace the entire assembly.
There are suggestions that you could get away by covering the splined shaft with some layers of "Tin Foil" and then tighten the wiper arm down over it. The number of layers to get a tight fit will vary depending on how badly the splines are worn. You may have to remove some foil at the end of the shaft to make sure the arm seats deep enough.
Another idea is to add a 7mm flat washer under the wavy washer. The inside diameter (ID) of a flat 7mm washer is just large enough to slip over the shoulder of the shaft. The outside diameter (OD) is just small enough to allow the cap to still fit over. The added thickness of the 7mm flat washer allows you to shove the wiper arm that much further onto the tapered arm of the shaft before the 6mm washer and nut bottom out on the shoulder of the shaft.
On a side note, over time, the wiper linkage can also become bent and worn. This is especially true if the wipers are used in a region where heavy snow and ice accumulate during the winter.
Recording Date: December 20, 2019
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