HingeJoint2d joint going crazy

I have a parent HingeJoint2d with a number of other connected HingeJoint2ds. The main hinge joint has no collider component and the child joints do have colliders. I find that after joining a certain number of child joints to the parent, the parent joint goes crazy and everything splits apart. If a add a non-trigger collider to the parent hinge joint then everything is ok. I've tried setting the mass and center on everything but it makes no difference without the parent collider. I guess I'm trying to understand why I have to add the non-trigger collider to the parent HingeJoint2d body.