Not applicability of reverse charge mechanism of st

Dear All,

        Kindly guide me that what are the situations when we dont avail the input tax credit of service tax ( Under reverse charge mechanism also). We are Automobile part manufacturing organisation and we receive all type of service i.e. GTA, Rent a cab, Manpower contract and work contracts also. And kindly differentiate with the abated and non abated rate in respect of Rent a Cab services. If possible kindly explain me with some examples for better understanding.