I'll be replacing my left rear quarter this winter and probably by myself so help if you can. A full quarter extends up into the roof sail where the seam is covered with bondo or whatever. How is it attached? Is it spot welded there or brazed? What would be the best proceedure?

what year you got?
Yes a Full quarter would go up to the sail panel.
To find the area where its at you need to remove the paint, use a da sander with like 80 grit paper. Once down to bare metal you will see two different colors in the metal if you still have the lead present. They used lead to HIDE the seem. You need to remove that lead in order to see the welded seem. What you can use to remove that lead is use very LOW heat. A torch turned down very low or even a propane bottle with a torch head like what a plumer would use would work. Work the leaded area heating the whole spot dont hold it on one spot which could warp the metal. The lead will melt right out.

BUT be warned treat that lead with the respect it deserves. Do this in a well ventialed(sp?) area and wear some type of mask to cover your mouth and nose. Lead is VERY TOXIC!!!

Once that lead is removed you can see the seem where the quarter is attached to the car body. The way it was welded from the factory is roof last(which is on top) then quarter then inner support(very bottom layer). In order to remove that quarter you need to drill thro the roof panel and the quarter but not the inner support.

Since you are somewhat new to the body biz I take it what I would do is just drill out the welds holding the roof on. use a 1/8 bit first for a pilot hole but DONT drill all the way thro just enough for a bigger bit. Now you should be able to take I believe a 5/16 bit will work, drill thro enough metal til the roof "POPS" loose, you shuld be able to see a ring of metal once its loose. Once all spot welds are drilled then you can work on removing the quarter welds.

You can do this 2 ways in my book, 1 drill thro both layers of metal(roof and quarter) or just drill roof layer then peel back roof and grind away the quarter welds. To peel it back just use a screw driver to lightly fold the roof lip back. That will give you acces to the under laying spot welds, you can then use a cutoff wheel and grind away the spt welds. Once again when the quarter is cut loose you will be able to see a ring.

In order to remove the quarter from the area it ataches at the drip rail you NEED to use a cut off wheel, its the only thing Ive found that will remove those spot welds.