The rear planetary assembly in GM 4L60 (700-R4) and 4L60-E transmissions frequently wears out and must be replaced. New replacement assemblies can be costly, and the availability of quality aftermarket assembly component parts are limited. Planetary assembly wear is generally caused by insufficient lube oil and/or excessive clearances. Lack of lube causes excessive heat in the pinion gear area and causes the roller bearings to gaul the gear bores and pinion pins. If there is excessive thrust washer wear or endplay, the roller bearings can run without fully contacting the gear bore, causing premature failure of the assembly.
Sonnax offers rear planetary rebuild kit 77731-RK, which includes all parts needed for a complete four-pinion planetary rebuild, with individual components also sold separately.