Starter cuts out

[AL in NY]

Having a problem with my starting cutting out just as the engine is about to start. I have totally rebuilt the starter with new field coils and brand-new armature. The teeth on the flywheel and the bendix are good. The only item I haven't replaced is the bendix spring. But my thinking here is a newer/stronger spring is going to make the problem worse because it will pull the bendix gear away from the flywheel even sooner. The starter turns the engine over very slowly, can that be the problem. The starter is grounded directly back to the battery and the battery is only a year old. What am I missing that will fix the problem.