This is a Teletype Model 15, first manufactured in 1930, and designed by Howard Krum. This was the workhorse of newspaper wire services well into the 1960s. Hundreds of thousands of these machines were made, they were built to last, and many still exist.
Full documentation is available, which is a big help.
This machine is dirty, slightly rusted, and missing a few parts. There's no serious damage. The motor runs, and the selector magnet works. Those are the only two electrical parts. So let's get started.
The first step was to separate the base, typing unit, and keyboard. The base has the motor and wiring. We put that aside for now. The keyboard and typing unit get an overnight soak in Simple Green and distilled water. This gets rid of most of the old lubricants. There's still a white residue on many parts, but that comes off with compressed air, Scotchbrite, and cotton swabs, and hours of work.
The next step is to check to see that all parts will at least move. Many of the typebars stick, the main shaft clutches are stuck, and the carriage return dashpot won't move at all.
The carriage return dashpot. All this just to give the carriage return a soft landing.
Providing some kind of soft stop for the typewriter carriage seems simple, right? All you need is a rubber block. But this is 1930 technology. Synthetic rubber hadn't been invented yet. Natural rubber dries out and cracks, doesn't behave well around oil, and doesn't have consistent properties. So when the carriage returns, powered by a spring, a pin on the carriage hits the bell crank (the end of which is at the right), which pushes on the piston shaft, which drives the piston inside the cylinder, which forces air out through an adjustable needle valve. The piston has a leather disc, with a large washer on one side of the disc and a slightly smaller one on the other. So the leather disc folds up slightly on the pull stroke, letting air go by, but provides a tight seal on the push stroke.
Anyway, the piston won't move at all. Pushing hard doesn't help. Fortunately, everything in these machines comes apart easily. So I take out the dashpot assembly and disassemble it. I get to the point where I have the cylinder end and the piston shaft, and nothing else, and they're still stuck. Taps with a rubber mallet don't help. Finally I have to use penetrating oil, wait a few hours, clamp the piston shaft in a vise with rubber jaws, and using a big pair of pliers, rotate the cylinder end. The piston moves a little, and I'm able to get it out.
What's wrong? There's a black tarrish material on the piston rod. Somebody used the wrong lubricant. (The official lubricant was whale-oil based; I use 0-20W synthetic motor oil. Using something that evaporates to a solid residue is lame.) Since the piston is a tight fit, the soak in Simple Green didn't get it out. A little work with Scotchbrite, and the piston rod and cylinder end are nice and shiny, and everything moves smoothly. While I have the dashpot apart, I give the leather disk a quick soak in Hydrophane leather conditioner, a silicone-based oil used for horse tack. The dashpot goes back together, gets a light oiling, and now moves smoothly.