torsion spring mechanical design

hi here,

i'm new to ptc creo parametric and to this forum .. so hello world.

i post here because i have a problem with mechanism design.

i tried to use spring mecanism. but,  if compression spring seems to work, torsion spring do not.

for explain my issue i want to model an assembly similar in function to a clothespin :

i modeled a basement  and these constraints (it seems to be ok)

and an axis with a mechanical pivot bond.

i used this bond to start my spring. starting works but when bonding should to be acheived, there is no display of the spring preview... and no possibility to set diameter... but validating is possible.

so i don't understand... 

i'll use this screenshot to explain better.

spring have to be linked to a slot in basement and to another slot in axis, like represented. i want to use this model to calculate spring deformation with moment -or other - force applied to this axis.

i hope anyone will help me

thanks

GF