I'm putting a new floor down and removed the toilet. The old flange was cracked to the point that it could not be saved. The problem is the flange was part of a pipe with a 5.5"OD and an ID of approx. 4.75". I'm having a problem trying to repipe a new flange. The old pipe was cast iron. If any one can give me an idea, it would be appreciated..

They sell a few flange repair/replacement kits. Some are metal, some are PVC.
The PVC ones seem more substantial.

Shunned gave you good advice. There are cast iron flange repair kits, (see image) that most hardware stores stock. However the metal ones will work best on cast iron. Good luck, Tom

You need to make sure that you have the right mesurements of the cast iron pipe that the flange is attatched to. A four inch pipe will have an inside measurement of four inches. The plumbing wholesale houses sell a replacement flange the will slip over the cast iron pipe, it has a neoprene ring inside and it has some bolts that you tighten from the top, as you tighten the bolts the neoprene compressses against the cast iron and makes a perfect seal and is tight enough to set the commode onto and bolt it down tight to the flange.

Thanks you guys. I did find something that has a good chance of working. It's a rigged [rubber?] inset that is a tight fit to the oversized cast iron ID, and has a ribbed ID that is a tight fit on the OD of the pvc flange w/ sleeve. The fits needs lubed along w/ a little rubber hammer help.
Thank's again.