What brand of cobra replica do I have?

[eschaider]

Tubular chassis are best made from thin wall high strength tubing, either 4130 or 4340. The construction requires TIG welding and a good geometric design. It is typically a preferred chassis design for race cars but not so much for street cars. One of the exceptions to that was the Mercedes 300 SL Gull Wing Coupe.

You begin to better understand the reason a tube chassis is a poor non-race car choice if you do a 300 SL restoration. The tubing is always subject to the normal rust incursions from external scratches that penetrate the painted (or other) protective covering applied to the chassis after fabrication.

What is not so apparent is the rusting / oxidation that occurs on the inside of the tube, in particular at the welds because very few fabricators (including Mercedes) will flood the chassis tubing with argon while welding to protect the weld on the inside of the tube. Although protected on the exterior, the interior of all the tubes is raw unprotected steel, inparticular at the weld joints.

You prevent weld blow out during fabrication by drilling small 0.060" holes in the tubing to allow the heated air to outgas during welding to avoid blowing out the weld filler before it can solidify. Those same construction artifacts are the entry point for moisture that will later invisibly but most certainly rust the chassis from the inside out making the car dangerous to drive.

300 SL restorations will frequently require significant portions of their space frame chassis to be refabricated with new tube because there is no repair other than replacement for rust damage. Looking at the condition of the chassis tubing in the underside shots I would be highly suspect of the chassis integrity today.

At the time of manufacture, depending on the skills set of the fabricator, it may have been a good race car chassis. Looking at the pics posted it lacks the symmetry and form of a well designed space frame not withstanding the potential rust damage on both the inside and outside of the tubing.

This was an excellent car to not buy. When these types of cars appear it is normally to a buyer's advantage to put as much distance between themselves and the car as possible. It is simply somebody else's headache that they have finally grown tired of and are looking for another person to assume — it is better not to be that person.


Ed