To set up a jointmulti first check that the R0 of the two referenced rigidbodies are set correctly and the Pivot of the joint (R0). R0 of the rigidbody is the center of mass and if your rigidbody is very light and very far from the joint's R0 position and the Kp/Kd are high then the physics can explode numerically. So you want to make sure that the R0s are set correctly before you continue.
In the second step I'd reduce the damping and spring constants (Kd, Kp) by a factor of 10 until it no longer explodes. The gear may collapse at this point and the prop may hit the ground and cause a reset but that is not as critical - it's the instant reset or glitching/jittering that needs to be taken care of first.
You can do this for one gear at a time.