I'm new to Blender so I may be overlooking something really obvious, but it seems to me the damping in the generic spring constraint does not work as intended.
I built a simple car (body, four wheels) with the generic spring constraint acting as suspension and entered realistic values for mass and spring stiffness in the various components. For the spring damping, I entered a first guess of 0.8, expecting the car to settle fairly fast after a drop.
Instead, it keeps bouncing and bouncing, and no reasonable value will stop it aside from a value of 1, which stops the bounce instantly - as expected. I did notice that I can enter values like .999999 and that almost works (although the value then shows as 1 in the number field) but that renders the damping incredibly sensitive to the number of solver iterations (and probably steps per second, although I did not test that) and is a completely unreasonable value for a damping coefficient.
Here's a .blend showing the problem: https://drive.google.com/open?id=0BwpD_rRXj8ceckFtM1NRR2FlVFU
As you can see, even with the spring damping set to .999, the oscillation will not stop.
So, my question is, is there a way to get the expected damping behavior out of the generic spring constraint, or should I report this as a bug? I've tried this in both 2.77a and 2.78RC, and the behaviour is the same in both.