I realize there is lots of other how-to’s on various forums about clock repair, but I just thought I would write up my experience with my VDO clock repair since it was a fun little father/son afternoon project, and I took a few photos and video and thought I’d pass it along. I found lots of bits of great info in other forums and posts on the subject, but they all seemed to leave a lot out....not implying my write up is seriously more comprehensive, but I’ll try to hit the main points that I hope may help someone wanting a fun little tinker project
I am in no way either a clock repairman, nor an electrical wizard. So I may, or probably will, say something wrong...feel free to correct me and add helpful things, this is all mostly for fun after all so we’ll keep it positive...no Debbie downers about how stupid the dash clock is and how terrible of time it keeps etc etc. I personally think it’s a cool little part of my original dashboard and gauge set so rants about replacing it with a later Quartz type clock, shift light, AFR gauge etc don’t need to chime in
Done disclaiming
My car is a ‘70T and honestly I don’t know when Porsche stopped using the VDO Kienzle electro-mechanical clock, but that clock specifically is what this post is about.
My clock never worked during my ownership of the car....going on 10 yrs now. I just thought it would be cool for it to work, regardless of how good of time it keeps. I did not open up the bezel of the clock to clean the plastic or the face, I only dealt with the workings of it in the back.
The white cover is held on with three tiny 5mm nuts, one of which is encapsulated in a little gray tamper “proof” cover. You will have to carefully break off this cover to access that third nut, no way around this. Tamper cover circled in red in photo.
The way these clocks work is actually super simple, however delicate. Basically there is a solenoid that once energized, only momentarily through a set of points attached to a flywheel, rotates that same flywheel maybe 60-90 degrees of rotation, and then for the next few minutes a spring rotates that flywheel back slowly until the points touch again and the process starts over.
On the most basic level, from everything I’ve read, and was the case with mine, the “failure” of these clocks is the soldered fuseable link connection. This isn’t really a failure but rather a design feature...when the solenoid pulls too much amperage/heat for whatever reason, the solder fails and the solenoid no longer receives 12V.
Part of the mystery, that’s more just misinformation, is what causes the electro portion of the clock to pull excessive amperage. Most writing I found suggests that it’s due to “gummed up” or sticky gears/shafts/mechanism of the clock, causing it to draw too much load to operate. This isn’t very true. The electro portion of the clock only momentarily operates the rotation of that one flywheel. And in the direction that flywheel turns during this momentary actuation is opposite of the direction it turns to actually operate the gears of the clock. That flywheel only has two places that have the opportunity to get “gummed” up or create drag. One is the axle (shaft) of that flywheel, and the other is a spring loaded “dog” that drags across the gear that it actuates. It’s unlikely that either point would have sufficient drag to cause an electro overload. So what it seems to me, is the actual points. Over time they get burned ( mine literally were...sooty dirty and black) and eventually fail to make proper contact, thus drawing excessive load and failing the solder joint. Flywheel circled in blue and red arrow points to the points.
So pretty much the drill is to clean everything carefully, dress the points however you see fit, and lube the mechanism, then resolder the fuseable link.
What I did was use, carefully, a can of electronic parts cleaner, a can of compressed air, and Singer sewing machine oil. The gears in my clock were a little dirty, and this process worked well to get it all clean and moving freely. I was very careful with how and what I lubed, I just used a toothpick dipped in the Singer oil to put a tiny drop on all the shaft “bearing” points and on the gears. I did not oil the jeweled bearings of the main timekeeping flywheel (I don’t know what to call it lol) You may choose to oil them, there seems to be varying opinions on the efficacy of oil on a jeweled bearing. But again I’m not a watchmaker or clock repairman so I dunno for sure. I’m sure there is specific oil available that is better suited, I only used Singer oil because that’s what I have, and the Singer repairman says it does not gum up over time like 3in1 oil. There’s other synthetic oils available for sewing machines that’s probably also good. This picture shows the jeweled bearings and the main flywheel:
Now, before even putting 12V back to it or fixing the solder joint, you can check to see how things are moving (especially the main timekeeping flywheel) by simply rotating the winder flywheel (the one with the points) clockwise (looking at it from the clock face) about 60 deg and let it do its thing. If the mechanism isn’t working smoothly you’ve still got cleaning/lubing to do.
Now if it’s working well, time to re-solder the fuseable link.
It’s very small, and in my case there was still a blob of solder attached.
The solder is low temp....I read somewhere it melts at 250 deg F but I don’t know if that true. That kind of solder is a little hard to find, so what I did was take apart a couple of heat activated wire butt connectors, and cut the ring of solder in half, flattened it out and held it with an alligator clip to do the soldering. According to the manufacturer of my butt connectors the solder used in then melts at about 280 deg so that’s close enough for me. I’ll say this...it’s low temp enough that a soon as your soldering gun tip touches it it’s liquid. I used a very tiny bit of flux and that helps it flow.
In this pic you can see the fuseable link apart (before repair) and the blob of solder left on there when it failed:
Here’s the butt connectors I used:
Here’s after the repair:
Since we definitely want the overload protection to be in place, and I’m not 100% sure my low temp solder joint will provide that protection, when I install the clock back in the car I’m going to put a inline fuse on the 12v supply wire. I’ve heard others have done this and I’ve read using anywhere from 1-3amp fuses....I have no clue how much the clock draws when properly working so I’ll start at 1amp and if it blows go up from there.
So that’s about it. My clock when left being tested before I reinstall in the car would lose about 5 min in 24 hrs so I turned the small adjustment screw on the back of the clock I about an 1/8th of a turn towards the + sign and it’s now keeping pretty close time.
I have a short video of the insides while running but I can’t figure out how to upload a video. I’m not really tech savvy if someone knows how let me know.
The clock ticks like any other mechanical clock, and every few minutes the electro points activation can be heard as well. Kind of neat, I think.