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The black faced clocks with the speed adjustment on the left hand side of the face and the time adjustment on the right hand side were Smiths clocks and the ones with the time adjustment in the center of the faced and the speed adjustment at the backside of the clock are VDO clocks.
As far as I know the '73 cars had the VDOs and the '70 - '72 cars had the Smiths. The black faced Smiths clocks were definately more reliable than the black & green faced ones on the '61 to '69 models but I don't know how they compared to the VDO clocks.
I have a working black faced Smiths Clock that came out of a '72 S so I'm guessing that it's not so rare to find one of those in working order. The VDO clocks had a thermal fuse in them that failed quite often so you most VDOs you'll come across will not be working but when you do find one in working order the chances are that it has been improperly repaired. This is because the thermal fuse was nothing more than a spring loaded contact soldered together with very low melting point solder. When something goes wrong with the clock it will start to draw more and more current through that contact. At some point the contact heats up enough to melt the special solder causing the thermal fuse contact to pull apart and breaks the circuit. The problem is that low temp solder is no longer available so most people just resolder that contact together with regular solder. This will make the clock work again but is not really the correct way to repair the clock and could cause real problems in the future.
The reason it's not the correct way to repair the clock is because regular solder has a far higher melting point than what the manufacturer specified for that thermal fuse. Obviously something went wrong with the clock before and the thermal fuse blew in order to protect the clock's electricals. If the thermal fuse was re-soldered with regular solder and something were to go wrong with the clock again, the clock will be completely fried before that thermal fuse gets anywhere near hot enough to melt regular solder.
I have fixed a few of those VDO clocks for people and I charge $50 USD for it. For that I will clean and lube the clock, and re-solder the thermal fuse with a low melting point solder which is as close to manufacturer specs as you can get. The solder I use has a melting point which is just 15C higher than what was originally used so I also solder an additional resistor into the circuit which makes the thermal fuse run approximately 15C hotter than it otherwise would at any given level of current going through the clock's internals. Adding this resistor then compensates for the higher melting point of the solder used on the thermal fuse thereby providing the clock with the same level of protection it would have if the thermal fuse had been resoldered with the original low melting point solder which, again, is no longer available.
If anyone is interested in having their VDO clock repaired as described above they can contact me at rojSPAM_OUT@telus.net. (Remove the SPAM_OUT part to e-mail me).
Roj
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