Another post mortem analysis

Maintenance/Repairs
1

If you’ve been here long enough, you know I like to take things apart to see why they failed. Sometimes, I fix them and have a spare. Other times they are shot but nice to learn how they work and what went wrong.

I think the last one I posted here was regarding the steering angle sensor for my Trailblazer that had repeated failures.

I recently bought a used Ford F150. There were lots of small stuff that needed attention. One thing I noticed is the wipers didn’t seem to work correctly on intermittent mode. They just wiped continuously no matter what setting that was selected.

Looking online, there are lots of different failure modes people complain about. The primary culprit is the multi-function stalk. Nobody had my exact failure mode. The replacement stalks are inexpensive at around $30 and pretty easy to replace. So I bought one and sure enough, it fixed the problem.

Then the curiosity started. Was it a circuit problem? What would cause this type of failure? So naturally, I took it apart to look. This may not interest you but if it does, read on.

The stalk has a small circuit board with a brush connector to interface to the truck column. It is encased in a liberal application of dielectric grease from the factory. I thought this circuit board might have the control electronics but no, it is just an interface board for all the controls (wiper, turn etc). Maybe the smarts are further up the stalk, inside the tip?

Nope, it is just a simple set of “switches”. A rotary switch for the wiper setting and a central push button for momentary.

Exposing the switch itself revealed the failure mode. The wiper “bumps” had worn completely through the traces and created a lot of copper debris that was trapped in the dielectric grease. In addition, the force applied rubbed through some of the traces and created additional short circuits between the adjacent traces. I had already removed the generous amount of polluted dielectric grease on the circuit board before taking the picture…

Looking at the bumps on the wipers, they don’t appear malformed or rough. Not like the steering angle sensor wiper that had sharp edges from shearing operation. These look fine for the purpose. The tension appears to be a bit excessive, to overcome any potential for oxidation over time. You can see from the images, the wipers wore through the tin coating and then through the copper base.

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5 Likes
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Thanks for the write up with pictures, I like stuff like this… :+1:
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Now how about doing that Twin TH400??? :rofl: :man_shrugging:

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It’s not broken :face_with_tongue:
(discreetly knocking on wood)

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4

I always wondered what was in those things, too.

The GM division I worked for made windshield wiper motors until they sold the business in the 80s. Basic wipers had a 2 speed motor and a park switch. The depressed park wipers had the 2 speed motor, a solenoid and a cam mechanism to pull the wipers down. When delay wipers became popular, a circuit board was installed to control the delay but I did not know how that signal was delivered.

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Love it! I used to do this for a living, mostly de-lidding transistors and IC’s and using the Scanning Electron Microscope to discover that somebody had not been careful enough about ESD protection.