Violent shaking when using position drive in Configurable Joints

I have the following scenario;

     (conjo 1)
   o--------O (pivot)
   |
   | (Conjo 2)            
   |
 [Mass] 

Conjo 1 is positioned at 9 o’clock. I use position drive to move it from 9’o’clock to 6 o’clock position. However, this gives me a violent reaction.

I tried to increase the damper value, but my mechanical contraption becomes sloopy pointing at 8 o’clock. So it seems that adding damper does not make my mechanical contraption points 9 o’clock anymore, however I have no violent shaking.

What can I do to reduce the violent shaking when I use position drive? Changing mass of rigidbody seems to have little effect.

Note: I use physics iteration at 100, and fixed time physics at 0.01.

It is described plainly here: http://forum.unity3d.com/threads/66871-Excavator-simulation

“-- I primarily focused on the physical simulation itself to achieve a stable rig and find ways to overcome some limitations of the physics joint system, mainly the fact that velocity drive is powerless at velocity 0 so all the joints that drive this excavator are wrapped with a system that switches from velocity to position drive when resting, this allow for a very stable and predictable solution. Using just position drive would cause problem as target angles gets further away from the current state, increasing energy and cause violent reactions. With my system, it is not happening. Very pleased with that. – Fabre Jean”