Breaking Benz: It's not always a wrenching win

Wrenchin’ ain’t easy. At least not for me. I find some victories but there’s certainly plenty of defeat as well. And today I’m sharing full-on lameness. I decided to replace the rheostat located on the back of the gauge cluster of my 1974 Mercedes-Benz 280 sedan.
This did not go as planned.
The W114 Benz has a seemingly easily swappable rheostat and I acquired the new part. I want to have working dash lights, after all.
To swap out the bad unit for the good one, I have to remove the gauge cluster. Disconnect the various wires and cables connected to the rear of the unit. Then unscrew, swap, and screw in the new rheostat.
Sounds easy right? It should’ve been… but I messed it all up.

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11 responses to “Breaking Benz: It's not always a wrenching win”

    1. Jeff Glucker Avatar
      Jeff Glucker

      Yeah I’ve since discovered (but not yet implemented) that most people say to just wire the two posts where the rheostat fits in. You connect them and you now have a dash that runs at full brightness.
      I don’t need to adjust the brightness on the dash to anything other than full because it’s an old dash anyway. So I’m going to go that route.
      I’m curious if I need to solder wire to each end or if I can buy a small length of wire and make crimped ends and connect it that way. That should work, no?

  1. Zentropy Avatar

    Props to you for being honest. I never, ever go into a project with the expectation of success, at least with the first attempt.
    Every time I wrench on my cars, my wife first asks: “So, how long will this take?”.
    This always sets me off, because I have no idea how long it will take. If everything goes well, maybe 30 minutes. If it all goes to hell, then sometime into next week. The truth is, we don’t work on our cars for efficiency or cost savings– we do it for the experience. Regardless of success or failure, we always learn something. And that’s the satisfying part of it all.

  2. Fuhrman16 Avatar

    I feel for ya dude. I’ve broken plenty of parts, both old and new, that I’ve tried to install. Plastic parts tend to be the worst. They typically don’t hold up to ham-fistery nearly as well as metal does.

    1. Tank Avatar

      Theres been a motorcycle in my garage that’s been sitting for about a year now, I took off a caliper because the bleeder valve was stuck open, I got it off the bike, got a new bleeder valve in, but now I can’t take apart the caliper to get it back on, nor can I get the brake line off. Its my fault for letting it sit outside for so many years when I didn’t have a garage or a driveway

  3. Lokki Avatar

    As the owner of an old Alfa, you and I just became buddies through shared experience. Before watching the video, I was going to suggest that the first rule of Italian cars was at play:
    “It’s always a bad ground.”
    However, after watching the video I realized that that is wrong and realized that the first rule of German cars was in play:
    The problem lies in the German obsession for perfection, and damn the complexity – full cost ahead!
    Still, I have a couple of thoughts to toss in, even though they come from my Italian perspective.
    1. Always try the cheapest solution first. On electrical parts with contacts that means spraying the part with contact cleaner, even new parts. Note that some old automotive trim plastics dissolve in contact cleaner so remove the part first.(Yeah, ask me how I learned that). On rheostats, I also always spend a few minutes cranking the knob back and forth all through the range to clean the coil. They get oxidized easily if they’re not exercised, and how often do you adjust the dash lights?
    2. Nothing electrical gets reassembled before the contact points have been cleaned till shiny, and then copious amounts of dielectric grease applied. It improves contact, and keeps corrosion at bay.
    3. I think I know what you did that broke the parts, although of course I am just guessing. Did you try to insert one bolt all the way in and tight before installing the others? Just as when reinstalling a wheel you must tighten the lug nuts in a pattern so that the wheel aligns properly, on a part with a long shaft you must tighten the bolts sequentially so that the shaft stays aligned straight in its hole. Otherwise the sideways stress can snap piece that holds the end of the shaft. Note that usually only German cars have tolerances tight enough for this to be an issue. On an American car, the factory just drills a 20 mm hole for a 4mm shaft, and puts on a big knob the cover the hole.
    4. Gnomical is completely right. I never expect a job I’ve never done before to go right, and it IS worth doing twice.
    5. Don’t kid yourself that you are going to be satisfied hardwiring across the contacts and skipping the the rheostat. You are a guy who is driven crazy by a small rattle in a 40 year old car. You would never be happy knowing that although no one can see it, you jerry-rigged something. You would frown every time the dash lights come on.

    1. Jeff Glucker Avatar
      Jeff Glucker

      #3. Yes, that’s totally what I’ve done.
      #5. Actually, I’d feel good knowing I tried a workaround… and to have it actually work! I would smile everytime the dash lights come on, with full brightness.
      We shall see what happens.

    2. Manxman Avatar

      The first rule for Italian cars goes for British cars, too. I seem to remember when the wiring harnesses of most cars, including my MG Midget or Ford Capri, weren’t much more complicated than my little Suzuki DR200. It’s amazing how contact cleaner and dielectric grease can clear codes on modern cars when used on the appropriate connectors.