The title says it all, folks. Mel Blanc guest-stars as a cab driver in this season 2 episode of The Beverly Hillbillies, "Granny Learns to Drive". Mel appears with Granny (Irene Ryan) during the first few minutes.
If memory serves me, I believe The Jack Benny Program had either ended or was wrapping up its CBS run around this time. Hadn't seen this before today, so I won't rate it.