Where did this term "chunk" come from?

When I was a youngster an out of towner visited my dad's gas station in Florida and was bragging about running over a 100 mph on his trip south. Gas mileage came up, and he commented he was running a 2.76 gear, and when he got to where his was going, he would just swap it out and "Chunk" it in the trunk.

It stuck for me.