No matter how long I have been at this, I am still amazed as to what people will do while building a car. Many of the things I see shows just how ingenious people can be. Then there are the things done which continue to prove mankind is still just one step above being an animal. Welding any spring, coil or leaf or torsion bar, fits this category.

I am sure the character who did this figured he had his reasons for welding the spring to the seat and probably believes he was one of the best engineers in the 'hood. 

During the welding process steel is heated to the melting point and the steel in the pieces being welded flow together. The welding rod or stick is used to create the electrical arc and to replace the steel which is lost and to add extra material to create a larger bonding area. Welding is a perfect way to bond low carbon steel. (we aren't talking about aluminum or special welding techniques, this conversation is limited to spring steel)

However, High Alloy spring steel does not react kindly to the excess heat generated in the welding process. The high heat causes spring steel to de-carbonized and to become brittle. The de-carbonization generally occurs in the section right next to the welded area. The weld may not break but I assure you the section of the spring right next to the weld will break.

In fact, simply striking an arc on a spring will create a de-carbonized area which will cause a failure to occur at that point.

Something everyone must simply burn into their brains is to -

 NEVER, NEVER, EVER WELD ANY SPRING

As you have correctly guessed another sad result is that the heating process also weakens the spring beyond the area next to the weld. In order for spring steel to become a spring the steel must be heated and cooled and then reheated in a controlled process. Once the steel has been tempered, heating it above 400 degrees will cause the spring to anneal and the spring will no longer support weight.  

Springs are part of a vehicles suspension and the suspension is part of the components which attaches the wheels and axles to the vehicle. You never want to do anything which jeopardizes the integrity of any suspension part. Heat and welding on any suspension part can be harmful and must be avoided.

Now Dennis what you need to do is get those welded springs off your car and throw them away. Both ends of the rear springs off an '88 Caprice were pigtailed, that is the end coils have a smaller diameter then the body of the spring, and the free height, out of the car with no weight on it, is around 17-1/2 inches for the Sedan and 14-1/2 for the wagon.

Take off the good spring and measure it's length, let me know your findings and we will set you up with the correct springs.

Also figure out why the springs were welded to the perch and fix it so they sit on the perch like they should.