It's been so long since I took the Mechanisms class..... I can't remember which connection to use. I have a lever with a spherical pocket in it. Into this pocket is a pin with a fully rounded tip, much smaller than the pocket's sphere. I can't make a ball connection and can't seem to figure out how to use the tangent of it (which is what it really is) as the translation constraint.
To put it another way, imagine trying to construct a joint in which a ball rides within a spherical socket whose radius is 3 times the radius of the ball.
Quick question about the actual degrees of freedom in your mechanism. Is the pin really free to pivot around the center of its smaller radius spherical surface, or does it actually pivot about the center of the larger radius socket? If the latter is the case you can add a massless, hideable surface to the pin and use that as a reference for a normal ball joint placement. If the former is the case, it seems to me that you have a non-simple connection that will not yield to the standard constraints. (It's one step more complex than if your pin could slide all around on a flat plane and pivot around the center of its spherical contact surface at the same time.)
I was able to do this with a couple of sketches in the components, one of the edge of the tip's radius and another in the socket that was offset from the sphere by the radius of the pin's tip.