clamber onto (something)
To climb onto something in a lumbering or uncoordinated manner. The bus swayed as the boys clambered onto it, whooping and laughing.
clamber up (something)
To climb something. Everyone else was able to clamber up the rope in gym class, but I struggled, thanks to my scrawny arms.
clamber onto something
and clamber in (to something); clamber onto climb onto something clumsily. The kids clambered onto the tractor and tried to start it. The wagon stopped and the kids clambered on. All the campers clambered into the bus.
clamber up (something)
to climb up something, especially in a particular way. The wall climbers clambered up the wall quickly. Tricia clambered up the ladder and cautiously went down again.