ガクンガクン
gakun gakun

To-Adverb

1. jerkingly

Onomatopoeia
くるま草地 くさち み、しばらくガクンガクンと はしって まったのです。
kurumawa kusachini tobikomi shibaraku gakun gakunto hashitte tomatta nodesu.
The car dove into the field and, after bumping along for a time, came to a halt.