Hammer technique for 7' grands

[Sherry]

Hi,
    I recently had 4 different jobs tuning 6'11" to 7' grands (Steinway,
Yamaha and Baldwin).  With each of the pianos I had the same problem.  I
would use short, sharp "jerks" on the tuning hammer to bring a string to
pitch.  I would feel the pin move (not twist but actually move) but the
pitch wouldn't change.  Then suddenly on the 5th or 6th stroke the pitch
would jump quite a bit above where I wanted it to be.  When I tried to lower
it to the correct pitch the would stay put and then leap back down below
where I wanted it.  Eventually I was able to get it to the right spot but it
was all very frustrating.  Is there a special (or different) hammer
technique that one should use with the larger grands or did I just manage to
get 4 difficult pianos?
        Thanks for the help.      Sherry