You can buy the new cast iron flanges, with the expandable O rings that push into the pipe or you'll have to do the old style or pouring lead onto a cast iron flange. The latter option should only be done by professionals.
If it were mine I would chip out the concrete down to the point where the pipe is solid then I would install a new closet flange.
Toilet flanges OUTSIDE of the pipe including cast iron and brass to lead
You have to take the lead and packing out that is holding the flange in the next piece of pipe. If your flange is broke where the toilet bolts go, this is very common. There is a repair available for this. It consists of two curved pieces of metal that are about 1/3 of the circumference of the flange. They go under the flange and give you a new place to put the bolt. They are a lot easier to use than replacing the whole flange.
Install a ty fitting on the stack in the basement then run it to the sink. Put it low enough to account for a fall in the pipe, to allow proper drainage. Be sure to install a waste and vent pipe to code for both fixtures.
If the pipe is No Hub cast Iron you can use a mission cap If the cast Iron is bell then you caulk in a cast iron plug If the cast iron is a spigot end you get a transition coupling either standard weight CI or extra heavy and then use a cast iron cap in the transition coupling
If it were mine I would chip out the concrete down to the point where the pipe is solid then I would install a new closet flange.
If you can get to the 6 inch cast iron, you could use a rubber coupler between the cast and the flange. If it is in the concrete, put a piece of 4 inch PVC inside the 6 inch and lead it in like you would a regular cast joint. Leave the 4 inch above the floor and slide the flange over it, screw it down and cut the 4 inch flush with the flange. They make just the flange that will slide over the pipe.
Toilet flanges OUTSIDE of the pipe including cast iron and brass to lead
Considering the waste inlet of the pipe of this pipe should be 4" possibly 3" you can buy an inside cast iron cutter .=You must measure the inside diameter and then buy /rent the one for the size you need THEN you can buy a new cast iron floor flange and use either a caulked joint (lead and oakum) or possibly a quick set type if the cast iron is no hub or standard weight=
What is actually broken the flnge ring rusted out and broke or the abs pipe? Abs pipe/flange broken: Use a ram bit to cut it out and install a new one. http://www.plumbingsupply.com/pvcsaver.html use a compression or expansion flange http://www.plumbingsupply.com/toiletflanges.html or just cut the pipe and put in a new one Flange ring rusted/broken: install a toilet flange repair ring or a spanner flange.
If you are a do it yourselfer, there are many adapters available to replace a broken cast-iron toilet flange. These adapters can be made of cast-iron itself or PVC. They are made to be inserted into the existing pipe where a rubber gasket is tightened to create a water tight seal. The adapter incorporates a new flange which is attached to the existing sub-floor. Other adapters even help in the case of damaged or rotten sub-floor around the waste pipe. If you do a search on "Repair Kit For Cast-Iron Closet Flange" you should come up with numerous options or you can visit your local pluming supply company who can provide you with both products and answers to any questions/concerns you might have. And if you don't feel comfortable doing this yourself after investigating what is involved, call a licensed plumber.
Clean the inside of the pipe and floor top with a wire brush. Apply silicon to inside of pipe and top of floor, you are making an airtight seal. Install lead dutchman into pipe and repair flange on top, which will secure the lead dutchman. You can now install your toilet as usual, since you have a flange for mounting your bowl ( this is assuming you are updating to a flange mount bowl).
Very carefully because if there is any moisture present and precautions are not taken the lead will react very violently and can cause blindness or death
Yes, it is done all the time
depending on your type of flange and pipe and the damage of the flange, if you have a PVC flange with just the bolt slots busted then you can screw in new bolts to the floor below the flange and still use the flange but if its broken where the wax seal sits then if your flange is lower then the floor you can use a insert flange that fits inside your old toilet flange with thin walls to keep the pipe size maximum. To replace the entire flange can be a job especially if its in concrete or in a floor joist because most of the time you have no room and if its cast iron pipe it can be even more of headache but in order to replace the flange you need to cut it out to where you can reconnect the pipe and flange by using a fernco or a no hub band. Sometimes it is impossible to replace because the flange can be on all close fittings and you pretty much have to replace most of the plumbing drain pipe to replace it properly which is why you want to try repairing your toilet flange rather then replacing it .
Cast iron is not threaded, steel pipe is.
was asbestos used in production of cast iron pipe