If by drive you mean the bendix that pops out to engage the engine, I do not know if that is available separately as an oem part. If it is not staying out while the starter is cranking your battery may be low on capacity. Have it load tested at an auto supply store. If your taking your starter apart to replace that bendix you should replace the brushes and clean it up at the same time. Usually when the brushes wear down and the commutator is dirty the starter does not get all the current it needs to spin fast enough to keep the bendix engaged with the engine.