Ultimate upgrade for the 9398 4x4 crawler with pendulum steering (no servo needed). I also made a pendulum steering file in the rebrickable link you can download and have a closer look
LEGO MOC Ultimate MK2 4x4 Crawler 9398 Upgrade by Cyborg-Samurai | Rebrickable - Build with LEGO
LEGO MOC 4x4 Crawler Control+ Rebrick by l1anchu | Rebrickable - Build with LEGO