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 Mini 9398 crawler (42139 Alternate Model) by technicprojects | Rebrickable - Build with LEGO
Wts Lego technic 9398, Hobbies & Toys, Toys & Games on Carousell
Extreme 9398 MOD - LEGO Technic, Mindstorms, Model Team and Scale Modeling - Eurobricks Forums
LEGO Set 9398-1 4 x 4 Crawler (2012 Technic) | Rebrickable - Build with LEGO
LEGO 9398 Technic 4X4 Crawler RC Truck Remote Control Off Road Rock Four Wheel Drive on 100outlets.com