How to Repair a Broken Exhaust Flange
The exhaust flange is in a very vulnerable location, and you may find that it gets damaged easily. If you don't repair the broken flange, you may find that you get other problems along with the break, including limiting the flow dynamic of the exhaust gasses, and even damaging the ground on which your car moves. Rather than be stuck with the broken exhaust flange, you should be prepared to mend it when you have a few spare hours. This job can be completed in a day, and will not be too difficult to be managed by anyone with a basic knowledge of car maintenance.
Step 1 - Clean the Flange
In order to be able to properly repair the flange, you will need to firstly clean it thoroughly. This is necessary to remove all of the rust, burned parts, and other exhaust products which could be on the end of the flange. It also ensures that there is no fuel or oil on the part that you will be fixing. Manipulate the broken part to reassure yourself that it will fit back into place, and then hold the broken parts together using a vice, or two if needed. If you are missing a part of the flange, or you have a very large piece broken off, then you should consider replacing the exhaust pipe completely. A small break, or minor crack, can be fixed using the broken parts.
Step 2 - Warm Up the Parts
Once you have the broken parts being held together by the vise, then you should use your acetylene torch to heat them. You should only use an acetylene heat source for this, and not just heat up the broken parts with any old flame. Remember that the exhaust handles a lot of toxic fumes, so be careful what heat source you use to melt the iron slightly. Once the parts of the metal turn red, and begin to bend, then you should use your brazing rods to move the metal around on the surface. Take your rod from one melted part to the other, passing the molten flange parts between the two ends. Once you have melted one side, and moved them together using the rods, move around to the other side of the car, and repeat.
Step 3 - Allow to Cool
Once you have successfully melted the broken pieces back into one, you should hold the flange in place until the metal has completely cooled. You will have to adjust the exhaust slowly to the cooling process, bringing the torch to and from the metal in increasing circles, so that eventually the torch is taken away from the pipe completely. When the metal has cooled, remove any protruding lumps with the steel file, and then remove the vise. The exhaust should now be completely fixed.