By Phil Carne, Alan Lockyer, and Todd Rudaitis
Phil Carney: One of the easy restoration items on a 356 that any one can do is knob restoration. It turns out that the knobs are soluble in lacquer thinner (not paint thinner). Make a little holder using a wooden dowel stuck in the theaded hole. Using the dowel stick, immerse the knob in lacquer thinner for 15 to 45 seconds or so (don't let it touch anything while in the lacquer thinner). Remove knob and use a stiff lint-free cloth to brush the surface so that all crazing disappears. You can even remove small nicks by reimmersing and rebrushing to fill them in.
Let the knob dry overnight without touching anything. I drilled a bunch of holes in a piece of wood and put the dowel holding the knob in the hole. The next day I polished each knob on a buffing wheel using blue polishing compound. Since plastic heats pretty easily, I assume a buffer on the end of a drill could also be used.
It is almost like magic how this process makes an old dull, crazed and cracked knob look like new. On my Convertible D, the original knob on the end of the turn signal stalk was cracked and wouldn't stay on. That knob was beige and the reproduction ones were black and just don't look like the original after painting. The lacquer thinner seeped into the crack on the original knob, melted the plastic and resealed it like new.
Been using it that way for 5 years and it is still like new. This approach works so well that the final product amazes you. And it's fun to do.
Todd Rudaitis: The miracle product is laquer thinner. Take the knob and dip it in the thinner just for a couple seconds. Then take a clean rag dampened with the thinner, and rub the knob until you start to see the finish "come up". You'll quickly learn the feel for when you need to turn, and remoisten the rag, you'll feel it "drag" on the plastic, you'll probably have to rewet the rag two or three times before the finish starts getting real nice.
Remember, you're actually removing a film of plastic, so don't go crazy. When you get a finish that looks good, let it dry for a few seconds, then use a separate cloth, and buff. You can follow with a wax if you want, but probably won't need to.
It helps if you screw the knob onto a bolt, then secure the bolt in a vise. This way, you can buff the knob like a "shoe shiner".
My ivory knobs were extremely "checked", but came back beautifully.....and all six took less than 30 minutes.
Alan Lockyer: I basically followed the method suggested by Todd Rudaitis (above). However, despite my knobs being badly crazed, I was nervous about using a solvent as aggressive as lacquer thinner. So I substituted methylated spirits (denatured alcohol), which worked beautifully.
After rubbing/smoothing each surface with a rag dampened with meths, I immediately dipped the knob in water to neutralize the solvent. No plastic at all came off on the rag. Seemingly, the surface was simply redistributed, resulting in a perfectly smooth finish. A final shoeshine buffing as described by Todd, and the knobs have shed 40 years, with no loss of "heft" or shape.
I might eventually add a coat of wax or clear acrylic, but so far I doubt this will be necessary.