The rear planetary assembly in 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 replacement parts necessary for rebuilding damaged rear planetary assemblies, 77731-RK and 77731-02K.