Property registered in 1980 in grandfather's name. Can I claim share?

First of all the fact that the property was registered before 1980 shall not make any difference to the present matter. Now, as the property was owned in the name of your grandfather's brother, the only legal recourse available to you is to find a partition suit on the basis of an oral agreement between your grandfather and his brother.

There are many such transactions whereby the family members enter into an oral agreement for jointly acquiring a property, even though the same might be registered in the name of only one of the family members.

In the light of various Supreme Court and High Court decisions, it is quite clear that as per Section 10 of Indian Contract Act, 1872 even oral agreement is valid and also enforceable through Court of law, provided the person claiming the right should establish the existence of such a oral agreement.

We shall have to prove the existence of the Oral Agreement and this can be proved by various factors such as that your grandfather had contributed to acquisition of the said property or if there were any witness to the said transaction, etc.

Was there any Huf in existence prior in time? Was properties bought from common funds? If you have some proof of the same you can file a Suit for partition and Mesne profits.