Tips for creating “Context Free Grammar”
Mmmm. 

Let me note that in fact $L =\{ w v w^R \mid v,w\in \{a,b\}^*\wedge|v| \text{ is even } \}$ equals $\{ v  \mid v \in \{a,b\}^*\wedge|v| \text{ is even } \}$.

Al strings in $L$ are of even length, and conversely all strings of even length can be otained by taking $w=\varepsilon$.

That should help.