Riding the cable cars beginning in the late forties it seemed to me most gripmen did a little "free wheeling" when going over a hump, albeit for no more than a few seconds. On one trip there was a problem with the grip on our trip so the word reached the Muni barn to send a replacement. The cable car was positioned over a removable metal plate, the old grip hoisted out over the hole and replaced with another. It didn't take very long to do. We probably waited longer for the truck to arrive.