"There are two types of inner CV in use, the Glaenzer (commonly known as a tripod or tulip joint), and the more common Rzeppa, with 6 steel balls - OEM axles use the Rzeppa for both inner & outer joints, most after market have a Rzeppa for the outer CV, and a Glaenzer for the inner CV - the inner joints on the OEM axles have a retaining ring to stop them pulling apart, the after market axles don't use them - this may be your problem."