  We establish a differential $d_2(D_1)=h_0^2h_3g_2$ in the $51$-stem of the
Adams spectral sequence at the prime $2$, which gives the first correct
calculation of the stable 51 and 52 stems. This differential is remarkable
since we know of no way to prove it without recourse to the motivic Adams
spectral sequence. It is the last undetermined differential in the range of the
first author's detailed calculations of the $n$-stems for $n<60$ [6]. This note
advertises the use of the motivic Adams spectral sequence to obtain information
about classical stable homotopy groups.
