If you are a lawyer or a judge, you will be certainly interested in knowing answer of this question from reliable sources.
The name of book is :
"The Keshvanand Bharati Case - The untold story of struggle for Supremacy by the Supreme Court and Parliament" by T.R. Andhyarujina.
The author is a top senior advocate of Supreme Court. The review of this book is written by P.P. Rao, another top Senior Advocate of Supreme Court who had attended each hearing of this case.
So the sources are authentic.
The following is a quote from this review article:
"The next chapter is devoted to question : "Did Justice Chandrachud changed his judgement?"
This is answered on basis of Justice Chandrachud's own version in his Judgement in Keshvananda.
The author has observed that Justice Chandrachud admitted that he was differing from the other judges after being with some of them for a part of time.
As recorded by him, the Judge denied the rumour that he was prevailed upon to change his judgement by the Law Minister and a former CJI."
.... Then the reviewing author compares his judgement not only in Keshvanand Bharti Case but also in ADM Jabalpur Case and says that one could not jump to definite conclusion about his thinking from his interactions with the judges sitting next to him.
Those who are interested in understanding how judges mind work, may do well to read this book itself.
So far as the Review Article is concerned, it can be found in law report 2011(12)SCALE page J-1.
Haresh Raichura
16/7/2013