by John Siple and Mr. Bubble Head
John Siple writes:
The analog clocks in older vehicles have an escapement movement and simple gears like any simple clock or wrist watch. The difference is in their mainsprings. VW clocks are wound by a little electromagnet that ratchets an arm attached to the mainspring. What happens is that a set of contact points closes a circuit to the electromagnet, which pulls an arm and tensions the spring. With a wound spring the clock just keeps working like a wound watch. As the spring unwinds the arm, which contains one of the contact points, slowly approaches the fixed contact point. At contact the electromagnet kicks in again and ratchets the spring. This cycle happens about once every five or ten minutes.
When these clocks fail it is often because the points get dirty or Oxidized [or because its small "fuse-wire" has come loose--look for signs of its remains and re-attach]. There is also an adjustment in the clock for regulating it. If it's running slow or fast you can adjust it. It's been five years and I don't remember the regulation details but I think they would be self-explanatory once you took a look inside the clock. Regulating a regular clock or watch is just a matter of changing the tension on the balance wheel spring, making the wheel spin faster or slower. Same in the VW clocks.
So if you have an old analog clock you might try a quick repair. The one in my van loses about a minute a day, depending on the weather. It is disgustingly reliable. It also keeps running even when you disconnect the battery for a few minutes. That's something the digital wonders can't claim.
Oh, by the way, don't try to lubricate or clean the balance wheel and escapement unless you know how to deal with balance wheel springs and watch pivots. These clocks will run for years without any lubriction. Mine has been going for almost 25 years now. It makes a very satisfying little "kerchunk" every ten minutes to tell me it's happy.
Which is all to say that it is not a constant voltage that makes old analog clocks run true. The voltage just winds them. The balance wheel spring regulates them.
Mr. Bubble Head writes:
I fix clocks all the time, sorta becoming a hobby for me. 90% of the time it's
a broken wire. This wire runs from the contact points to a little metal arm
on the coil. This little are has a sort of double end on it. How do I
explain this? It's a little arm and on the end of it is a taco with a hole
in it. The arm bends enough to reach the points, and then you can squeeze the taco on to the contact points. I have fixed several clocks this way! You may also want to dress the points up a little, other wise they arch and slam the arm back when the make contact.