  The deuteron, NN analyzing powers A_y, and the singlet scattering length show
great sensitivity to the $\pi NN$ coupling constant $g_\pi$. While the pp A_y
data favor $g^2_\pi/4\pi\leq 13.6$, the np A_y data and the deuteron quadrupole
moment imply $g^2_\pi/4\pi\geq 14.0$. The two diverging values could be
reconciled by the assumption of (substantial) charge-splitting of $g_\pi$.
However, the established theoretical explanation of the charge-dependence of
the $^1S_0$ scattering length (based upon pion mass splitting) is very
sensitive to a difference between $g_{\pi^0}$ and $g_{\pi^\pm}$ and rules out
any substantial charge-splitting of $g_\pi$. Thus, there are real and large
discrepancies between the values for $g_\pi$ extracted from different NN
observables. Future work that could resolve the problems is suggested.
