While I am in the process of restoring the complete undercarriage of my 74 Coupe deVille for cosmetically reasons - I also had to decide what to do with the rusty driveshaft.
When the car was built, Cadillac and all other car companies did not bother to protect the bare metal driveshafts in any way, so they already had surface rust on them when they were delivered new…

My initial plan was to use a wire brush to knock of the rust and just paint it black like most people would do.
But I then decided that I wanted to go the extra mile, do it properly and put it back into the condition it was when it was built.

I wanted to remove the rust chemically in a rust dissolving fluid that is normally used for de-rusting fuel tanks, but I had no idea how I could soak such a long piece in this fluid.
I came up with the idea to just use a big tarp and put some wood to the sides, put the driveshaft in it and fill it with rust removing liquid. This worked out really well.

It took about 48 hours until all the rust was gone.
After a little of the rust was gone I discovered the remains of the 3 factory markings on the drive shaft. There were three rings painted onto the shaft - two in blue and one in black. I found some small traces of the paint during rust removal. I wanted to re-apply them once the shaft was finished.

When the shaft was fully de-rusted I found out that flash rust would come back literally after only a few minutes. Thats why I decided to paint the shaft to replicate the factory appearance.
I used Eastwood Detail Gray to mimic the original look of bare metal. Before applying the paint, I used self etching primer on the bare metal.
When all the paint was dry, I added the finishing touches with the three color rings.

I´m very happy how it turned out - it looks great. You can see more pictures of this project here.

The driveshaft before…
The location of the first two factory markings. I measured them to make sure that I could replicate them when I painted the driveshaft. The first two markings were (light) blue. edge
The location of the third factory marking. I measured it to make sure that I could replicate it once I painted the driveshaft. This marking seemed to be black once.

I soaked the driveshaft for 48 hours in rust removing liquid and used these two brushes to agitate it into the rust.
This is how it looked after soaking for 48 hours. All the rust was completely gone and only bare metal was left.edge
The finished drive shaft.
The replicated factory markings on the drive shaft. The correct shade of blue color was only a good guess - I think it comes pretty close to the traces of paint I had found.
Back in the car to be able to move it around.