To really hit your triceps try some tri-sets. Here is a tri-set routine that I would normally do to work the horseshoe like muscle.
Start with Triceps Extension with bar for a maximum of 8-10 reps. When you can't do any more reps with it, straight away continue with Close Grip Presses till you reach another failure. Once you can't do any more reps head to the Triceps Push-down machine and using the V shaped bar finish with 10-12 reps.
Perform 4 sets like that with 2 min. rest in between them and your triceps will be in for shock.