  We present the first direct measurement of the $W$ production charge
asymmetry as a function of the $W$ boson rapidity $\yW$ in $\ppbar$ collisions
at $\sqrt{s} = 1.96$ $\TeV$. We use a sample of $\wenu$ events in data from 1
$\ifb$ of integrated luminosity collected using the CDF II detector. In the
region $|\yW| <$ 3.0, this measurement is capable of constraining the ratio of
up and down quark momentum distributions in the proton more directly than in
previous measurements of the asymmetry that are a function of the
charged-lepton pseudorapidity.
