Have they gone into a "T" position? One will basically have his face at the others midsection. You can get them to breed by lowering the water temperature rapidly by pouring in colder water than normal, which acts like a spring flood which normally triggers them to spawn in the wild.
Try lowering the temp in your tank and increasing the water flow. They are tough to breed from everything I've read, but when it comes to spawning season they like cooler water. Just be careful not to make it too uncomfortable for your other fish.....And remember, they are egglayers and will lay them on plants and decorations sometimes one at at time......... up to 1100.....at once......that's a lot of fish, but that would be way cool!