Pg_basebackup does not do aything

Hello,

I have a configuration in master (A) /slave (B) streaming replication.
I bought a third server (C), and I want to use C as my next master server.
In a first time, i would like to sync C as a slave, and in a second time
i would like to promote C to master, and change my current master (A) to
slave (the third server (B) would be out of the equation)

So I tried to use pg_basebackup on C, either synced on B if possible
(cascading replication), or in A if it is needed, but when i use the
command, nothing happened

My command is  :  pg_basebackup -D /data/postgresql/9.3/main -P -v -h
MASTER -U replicator -X s
(this command worked when I used it on my current slave)

In view pg_stat_replication on master, I have this (1st is my streaming
on slave, 2nd is the pg_basebackup I try to use)

  506 |  5828189 | replicator | walreceiver      | 172.25.1.2
|                 |       48022 | 2014-06-25 21:54:34.561107+02 |
streaming | 3E3/597E0000  | 3E3/597A0000   | 3E3/597A0000   |
3E3/5977F290    |             0 | async
  512 |  5828189 | replicator | pg_basebackup    | 172.25.1.3
|                 |       45573 | 2014-06-25 21:54:39.324114+02 |
backup  | 0/0           | 3DD/BDF88000   | 3DD/BDF88000   |
3DD/BDF67C98    |             0 | async


I try to use it on master and slave, but it does the same thing (nothing)
I am wrong in the way I try to use replication ?

Thanks
Thomas