The trouble with stuck cables and gaseous gas

Many of the mechanical issues that vex us are auto independent, which is to say, universal. I decided to tackle two of them.

Hagerty member Gary Linsky writes: I am the original owner of a 1976 BMW 530i. The speedometer has a twitch in the indicator needle at low speeds that I attribute to gummed-up lubrication of the speedo cable. I’ve read warnings about lubricants walking or wicking up the cable to the speedo head, a condition to be avoided.

Both Hemmings and The Garage Journal recommend lubricating speedo cables with a spray can of white lithium grease, and I concur. It’s heavy enough that it stays in place and doesn’t run out the bottom end of the cable. Some posters report success with silicone or graphite, but graphite seems a little light to me. If you’re going to use lithium, I wouldn’t worry about cleaning old lubricant out first, but if you’re concerned about it, you could spray brake cleaner in one end and out the other. Be sure to blow it out with compressed air before introducing fresh grease so it doesn’t cut it. If you’re using graphite, though, I would clean it out first. And even though this isn’t one of your symptoms, if a speedometer cable will barely turn, you could first try to work it free with a penetrating oil such as SiliKroil, followed by lubrication.

Hagerty member Victor Witman writes: I have a 1948 Pontiac Silver Streak. It has a straight-eight engine, a six-volt electrical system, and an automatic transmission. In 2010, I had the engine and carburetor rebuilt. Now, on hot days, when the engine is hot and idles for a time, the car will run like it is out of gas, sputtering and then shutting off. It is hard to restart, and if it does, as soon as I put it in gear and try to move, it will shut off. After I let the engine cool down, it will start up and run like normal. I did not have this problem before the rebuild.

You describe textbook vapor-lock symptoms, which are caused by fuel in the line turning into a vapor before it can reach and fill the carburetor’s float bowl. The exact mechanism is referred to as “vaporizing” or “boiling.” These are two slightly different phenomena, but the result is the same—no liquid gasoline in the carb. Hot weather and high underhood temperatures create the problem, which is exacerbated by anemic engine-mounted mechanical fuel pumps that pull the fuel at a low pressure from the tank. If you want to be certain, you could temporarily replace the gas line into the carburetor with a transparent one and watch as the fuel goes from a liquid state to a gaseous one.

It’s possible that a fuel line is now routed closer to the hot engine than it was before the rebuild. You can try moving the fuel line or encasing it in a reflective sheath, but the long-term cure for vapor lock is higher fuel pressure, and the way to achieve that is with an electric fuel pump, mounted close to the fuel tank, that pushes rather than pulls the fuel. There are many six-volt fuel pumps, but the cleanest way to do this is with an in-tank pump. Tanks, Inc., sells an in-tank pump for your car, but it’s 12-volt, and your car is six-volt. I spoke with Tanks, and the company said it could sell you the flange and pick-up tube, and you could connect a generic six-volt submersible pump to it. Tanks would be happy to discuss the specifics with you (, 877-596-3842).

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