G14 starter issue

[mayberry]

My '96 G14 wont start if i "tap" on starter/generater it will turn over a little(not a full revolution-maybe 1/4 turn with each tap) I am getting correct voltage all the way through . I removed the starter/generater and checked all the brushes and they all have plenty of life left in them allthough the armeture did look a little "dirty" where the brushes ride . I took it to a local auto parts place to have the chek it out , they hooked it up and it spun freely without any noises . Should it have been under a load (as if it were turning motor) to test properly? Does the movement when it is "tapped" idicate anything