I just installed a new mainspring in a Waltham 6s that has a motor barrel. When I try to wind it I can here something slip. I had the darn thing apart too mant times to count. The end of the mainspring looks to be hooked,and the inner coil is hooked to the winding arbor correctly. What else should I look for?

Larry,
My best guess is thet the outer end of the spring needs to be 'curved' more in towards the barrel arbor. These Waltham springs usually come from the factory with the end too 'straight'. They will hold when the spring is relaxed, but as the spring is wound they will lift off the outer barrel hook.
Be careful bending the spring end. It needs to be curved right where the hole is, so the spring is weaker at that point and is more likely to break, ruining the spring.

Thanks Ed,I'll give it a try and let you know what happens. BTW,I called this barrel by the wrong name. I sould have called it a safty barrel.