Instruments and switches (54)
Drawing of the instrument panel for the Mercedes-Benz type 219, © Daimler AG
Disassembly and restoration of the individual parts
The instruments were in a decent shape but as usual I tried to aim for a “like-new” state with all parts of the instrument cluster or as it is called in Mercedes Ponton-language, combi instrument.
First the front of the cluster was removed from the cluster itself. As you can see in the third picture above, the old grey vinyl was dirty, discolored and in an overall bad shape, both from usage and also due to the storage and handling during the restoration.
After that the chrome frame went off. Underneath it you have three sealings. After that you peel off the instrument glass. As you can see there are a couple of rubber sealings glued into the frame, probably for vibration dampening for the glass. From Ka-Ja Tachodienst I got a new set of rubber.
Since the chrome frame had some pits and cuts it was sent for re-chroming together with the clock’s frame.
The we have a couple of pictures that show how the vinyl is glued onto the frame.
For protection and a clean surface for the new Roser red vinyl, the front was brushed and repainted. As you may understand that paint will not be visible.
When it comes to the disassembly of the base plate, be careful when you remove the foam rubber profile that is glued onto it and which seals against the front of the combi instrument. Don't "drag" it off the plate because then it will end up like mine, two sizes too big (see below) or you may brake it. I haven't been able to find a replacement. Next step was to remove the old lamps, cables and different instruments from the base plate.
The front and the parts that were restored by Ka-Ja Tachodienst
The first picture below shows the old water temperature gauge and sensor and the second the restored. Ka-Ja Tachodienst did a complete overhaul incl replacing the capillary tube and tested the complete unit.
The first two pictures show you the original status and the third the restored and tested oil pressure gauge.
The first and the sixth picture show the disassembly of the speedometers base plates. The fifth shows the wear on the gearwheels and finally you have the repaired and tested speedometer.
The Ponton fuel gauge consists of two parts, the fuel gauge itself as well as the fuel sending unit that is mounted in the tank. Both units were restored and tested together.
Finally, we have the lamp cluster in the Ponton combi instrument containing control lights for the blinker, choke control and main beam light. This one I handled myself. First the cluster was desoldered from the base plate. Then the front was removed and the small net and the colored plastic tabs were carefully cleaned. New lamps were installed, Osram 3796 12V 2W. Done!
First the lamp cluster was mounted and its related cables soldered. Then I started to mount the different instruments. See to that you align them correctly. This can be done in two ways; when you mount the instruments onto the base plate and/or by carefully loosening the screws that holds the instruments' fronts.
As mentioned above, be careful when you remove the foam rubber profile that is glued onto the base plate. Don't "drag" it off the plate because then it will end up like mine, two sizes too big (see picture). It was a bit problematic to "compress" the profile and glue it back. Doesn't look perfect but it seals against the front of the combi instrument as it should.
Testing the fuel gauge
After the assembly of the instrument cluster I decided to test the fuel gauge and the corresponding fuel sending unit (or "Electric transmitter for fuel indication" as it is called in the spare parts catalog). The workshop manual gives you all the necessary values for this test. Would be a walk in a part. Right…
Excerpts from Mercedes-Benz Ponton Workshop manual regarding testing of fuel gauge
First, I tested the fuel sending unit. I choose to test if it gave the correct Ohm-values for full, half full and almost empty tank. With the battery and instrument cluster disconnected you measure the resistance between ground and the contact labeled “G” (in the pictures below it looks as if battery and instrument is connected, that is not the case). I mounted the unit in a stand for a micrometer and positioned it according to the instructions in the workshop manual. With the help of two pieces of cardboard, cut to prescribed height for "full" and "half full", and a good-looking nut, with the height of an "almost empty" tank, placed under the plastic float I could measure the resistance given by the unit’s internal coil.
Problem with the "evil eye" and my tries to remedy it
The Ohm-measurements were on the spot. Next, I connected the fuel sending unit to the fuel gauge’s via the instrument cluster’s cable harness. The fuel gauge showed the correct amount of “fuel” as well. Last test was the “evil eye”, the red light that indicates that you have very little fuel left. It turned on as it should, after a couple of minutes. But then it went out after 4-7 minutes. That’s not correct. The “evil eye” should shine until you shut the car off or fill the tank (over the 5-6l threshold). I tried to make a new test but that didn’t work until I had waited at least 20 minutes. Did the bi-metal contact that controls the “evil eye” overheat in any way?
So, I took the gauge out of the cluster and tested it again. The light turned on as it should and didn’t go out even after another test or two. Hmmm… Where could the problem lie? Did it overheat due to bad air circulation when mounted in the cluster? Sounded odd, how would it then be when it was put into the car?! Bad solder joints or even a bad cable harness (which still had the original cables from -57)?
I went for the two latter possible causes and managed to find new wires with the correct, original color coding in Germany. Delivery took 4w as usual when Deutsche Bundespost and PostNord in Sweden are involved. You cannot stress in the restoration business.
I desoldered the wires from the connections in the base plate of the cluster and dragged them out. Having taken the protective tube off the wires I noticed that the ground wire was stripped from 5cm after the contact. Why it had been stripped I was never able to figure out. I thought that this may had been the cause, some sort of short circuit, but unfortunately, as you will see below, that was not the case.
Drawing of the instrument cluster cable harness
I started the soldering with the joints on the baseplate of the instrument cluster since I have had problems getting nice solder joints when the wires were cut to length. If I would do this work again, I would however start at the socket end.
Layout drawing of the instrument cluster
While making the new harness I also found out that the original solder joints on the socket were not only formed like cubes, but also looked frosted/crystalline. Were they so called “disturbed joints” or had they used another solder? I never found out. I used a large soldering iron directly on the wires to be able to get them out quickly without melting the “solder cubes”. The solder that got stuck on the wires did also lock funny/strange…
In two last pictures below, you can see that the solder joints in the female contact on the main cable harness are not formed like cubes, but cylinders!
To get the new wires soldered deeply enough into the cubes on the socket I drilled a hole in each cube. The wires were then soldered one by one, being hold steady by a “third hand” whose jaws were covered with tape to protect the cable insulation.
As you may understand it was a bit tricky to solder these wires with such a short length sticking out below the protective tube. So, start your soldering here…
Even though I checked everything 10 times I of course managed to mix two wires up. I noticed it just before I was going to tell my wife that the cluster was finally done. The wire order in the pictures below are however the correct one.
Layout of the instrument cluster socket wiring
With the new cable harness in place I happily hooked everything up for new tests. Sadly, it didn’t work now either. After further research I was sure the bimetal overheated in some way and turned the “evil eye” out prematurely. Looking closer at the contact I realized that the paper wrapping on of the coils seemed to have slid down. You can see this in the fourth picture. In the fifth picture you can see the paper that protects the coil and how close it is to the other part of the contact.
Firstly, one paper wrapping had slid down. Secondly, the wrapping had started to loosen up, the old glue probably didn’t hold any longer. I suspect that when the coil got hot it, together with the wrapping, expanded. And since the distance between the paper and the other part of the contact is so small it disengaged the contact and the “evil eye” turned out prematurely.
Even more problems before the solution
First, I tightened the wrapping of the contact part that is closest to the gauge’s base plate. With a pincette and glue that was not difficult. Then I tried to push the other coil with wrapping upwards and then tighten its wrapping. I almost managed to do that, but unfortunately, I broke the tiny coil wire on the same time. After that the “evil eye” didn’t turn out after a couple of minutes so from that perspective the gauge worked. But it turned on after only 20 seconds of “empty tank”.
I never found a source for this tine wire. It’s said to have very specific specifications in terms of resistance and only ~5/100 mm thick. E.g. has the fuel sending unit of a /8 (W114/115) a wire that has a specific resistance of 292 Ohm/m. If the Ponton fuel gauge has the same wire I was never able to figure out. I got a source for the wire, VDO, but they turned my request down. Let me know if you know the specifications and/or know where to get it.
When you look at the pictures below, remember that the gauge and the cluster are not “laying”, they are “standing up” ;-).
Below you can see the wiring diagram of the “evil eye”, the fuel reserve lamp. I have not opened up the fuel gauge and studied the components and wiring of the needle so that is not depicted here.
Electrical scheme of the fuel gauge and its fuel reserve lamp with the bi-metal contact
Maybe I’ll continue the search for the wire and repair my old gauge just for the fun of it. But to get some progress with the restoration I decided to search for a new gauge. Karasch could quickly provide me with a NOS fuel gauge.
With the new gauge in place everything worked as it should. Now it was time to finalize the front plate. Based on the old vinyl I cut new pieces of 1079 “Roser red” vinyl and glued them onto the front plate. Most of the vinyl on top of the front plate will be covered by the wood that lays on top of the dash, just behind the wind screen. The frame was re-chromed, and I got new 2mm foam rubber from Ka-Ja Tachodienst to place between the frame and the glass pieces. The assembly was easy. Insert the tabs of the frame into their holes in the front plate. Carefully, but firmly, press the frame into a tight position and then turn the tabs 90 degrees. Done.
Then you assemble the base plate with all its instruments with the front plate, taking care of getting the “big” foam rubber in place. Carefully, but firmly, press the base plate and front plate together and tighten the screws on the backside.
The cluster is beautiful and knowing that everything is 100% OK makes it even more beautiful. Now it’s just a matter of making some progress with the rest of the restoration so that I can put it where it belongs, in the dash.
The completely restored instrument cluster
This is a mechanical clock. A lot of people have recommended me to replace it with the later, electrical version. For me that’s a big No. Winding the clock is for me something special; you close the door, settle in and wind the clock as a preparation for the trip. And there is nothing more relaxing than coming home with the car, parking it in the garage and listen to the clock’s tick-tack for a couple of minutes. Winds me down…
The cover glass of the clock was broken and the small rubber sealing that sits on the shaft where it goes through the glass was old and dry. New was ordered from Ka-Ja Tachodienst together with the new rubber sealing for the shaft. The chrome frame was taken off. On the rear-side there was rubber melted (?) into it, I assume for vibration dampening. After pealing it off the frame was sent for re-chroming since my father have had it off for servicing of the clock and therefore it was slightly bent and damaged.
I also wanted to have the clock mechanism gone through. Hence, I had a watchmaker go through it. There was nothing to repair or replace except dirt and old, hardened oil and grease. That was removed and the mechanism re-oiled.
With everything gone through and frame re-chromed the assembly was easy and the result perfect.