try this

Author: njwhite

src/plots/cartesian/axes.js

@@ -2915,12 +2915,11 @@ axes.drawGrid = function(gd, ax, opts) {
         .classed('crisp', opts.crisp !== false);
 
     ax._gw = Drawing.crispRound(gd, ax.gridwidth, 1);
-    ax._gd = Drawing.dashStyle(ax.griddash, ax.gridwidth);
 
     grid.attr('transform', opts.transFn)
         .attr('d', opts.path)
         .call(Color.stroke, ax.gridcolor || '#ddd')
-        .style('stroke-dasharray', ax._gd)
+        .style('stroke-dasharray', Drawing.dashStyle(ax.griddash, ax.gridwidth))
         .style('stroke-width', ax._gw + 'px')
         .style('display', null); // visible