visualizing grid AND contour lines

Hello,

I am struggling with a potentially easy problem in matplotlib: I have some 2D data
which I visualize using matplotlibs contour function. However, besides the
contour lines itself I want to visualize the underlying grid as well which I do by setting ticks for
each data point on x and y axis and setting the tick labels to void:

figure()
ax=gca()
ax.set_aspect('equal')

xax=ax.xaxis
xax.set_ticks(X[0,:])
xax.set_ticklabels('')

yax=ax.yaxis
yax.set_ticks(Y[:,0])
yax.set_ticklabels('')

contour(X,Y,g,0,linewidth=4)
ax.grid(color='r', linestyle='-', linewidth=1)

Here, X, Y are the coordinates of my grid created with
X, Y = np.meshgrid(X, Y)

So far everything is fine and I have my grid. However, I also want to have some tick labels
on the x and y axis. I tried that using twinx() but that has the result
that
i) the aspect ratio is lost (which I have set with ax.set_aspect('equal'))
ii) the grid-lines are re-set to the major ticks of the newly created
axis.

How can I achieve both: i) having my 2D grid vizualized and ii) having some
ticks and labels along the x and y axis.

Thanks for any help and greetings from Sweden

Michael