Ultima adjustable ball differential

Parts & installation

Manufacturer documented

Vehicle: Kyosho Ultima30625
Position: center
Change: Replace the stock rear bevel-gear differential with one OTW101C ball differential, without its belt pulley guide.

Sold packs for one vehicle

Part	Qty
OTW101CBall differential, one rear assembly	1

Manufacturer assembly recipe documented. No independent test of this exact target was performed.

Scope is the 30625 Ultima reissue. Buy one OTW101C for the single rear differential; do not buy two merely because 4WD Optima/Javelin applications use front and rear units.
Page 12 says not to use the OTW101-01b pulley guide. Retain the original gearbox bearings and housings, spur/slipper assembly, suspension, motor, radio and body.
With the standard shafts, insert three O-rings from the spare-parts bag into each side. The manual explicitly says those O-rings are unnecessary with optional OTW125C universal shafts. OTW125C is an alternative, not a mandatory purchase.
Open the rear transmission, replace the bevel-diff assembly and rebuild the gearbox following pages 12-15. Follow the actual OTW101C package instructions for ball-diff grease, preload and maintenance; ordinary gear-diff oil is not a substitute.
The installation is documented by the factory. No controlled improvement in grip, durability or speed was verified. The setup and maintenance burden is greater than a sealed bevel-gear differential.

Maker instructions and assembly diagrams for the stated parts and configuration.