Metal geared servos are recommended for these applications

Premium Digital Servo

The HS-5087MH digital

Kadee #558 Self Center Truck S-2 7OT Roller Bearing 33"

but now with a ball bearing supported output shaft and Karbonite gears

Tekno RC TKR4188 M5 5mm Bore Mod 1 Pinion Gear (28T) T-Maxx Parts Metal geared servos are recommendedTekno RC TKR4188 M5 5mm Bore Mod 1 Pinion Gear (28T) This is the 28 Tooth M5 Hardened Steel Pinion Gear from Tekno RC. Features: Ideal for 1 8 scale and other MOD1 pinion applications Constructed of CNC machined steel, lightened and hardened for durability Standard length shank Number of teeth laser etched on shaft Includes: 28 Tooth Pinion Gear, M5 Set Screw Specs: Number of Teeth: 28 Gear Pitch: MOD1 Hole Diameter (Bore): 5mm