[T3] Why early clocks fail

[Jim Adney]

I just fixed an early (up thru '70, the ones with the white plastic 
backs) clock for someone who asked what goes wrong with them. I 
thought this might be worth sharing with everyone.

These early clocks use a solenoid to wind the clock every minute or 
so. When the spring winds down a bit this lets a set of points make 
contact, energizing a solenoid which "kicks" the winder and opens the 
points. I believe this is typical for all car clocks up to around 
1970.

There's a "fuse" in these clocks that opens up. This typically 
happens if the car is left in storage with the battery installed. As 
the battery discharges, it gets to the point where no longer 
sufficient voltage to kick the winder, so the points stay closed and 
draw current continuously until the fuse blows. The clock normally 
draws current for only a fraction of a second, and that current 
normally never gets large enough (or long enough) to trip the fuse.

The "fuse" is actually a tiny rivet made of very low melting point 
solder. I repair it by melting it and rejoining the connection. I 
also add a diode across the solenoid to minimize arcing when the 
points open. Then I flush out the works and lubricate each of the 
pivots with clock oil. The repair is usually pretty straightforward, 
but these clocks never kept very good time.

In 40 years, I've only seen one of these clocks where the bearings & 
pivots were actually worn out.

The moral? Disconnect either the battery or the clock if you park the 
car for a long time (months.)


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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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