Originally Posted by voam
Could I just cut about a foot above the crack and replace the section? Is that T-shaped joint still OK? Would I be able to remove the part of the pipe that that is still in the T shaped joint or once these things set is it impossible to clear out?
Nope, the fittings are permanently glued together. Since the fittings are so close together, you'll need to replace the entire assembly. It may seem like a lot, but it's just a sanitary tee, two street 90s and a regular 90. You'll also need to get a length of pipe, ABS cement, a repair coupling, and 1-2 regular couplings.
Make sure you fit everything together before you start gluing. Also make sure you plan out the order of assembly so you can get the last fitting installed without "painting yourself in a corner." The repair coupling will make it easy, but they're a little more expensive than a regular fitting, so if you can work out a way to avoid it you'll save a few $s.
BTW, I would make the horizontal section as long as you can get to fit. The existing is pretty close to an s-trap which is not allowed since it's easy for it to get sucked dry.