Weird behavior with Gruen 385 movement

[Jfree]

Hi All,

My buddy at work just got his grandfathers old 1947 Gruen very thin watch for Christmas.  It has the caliber 385 movement in it.  I don't think the watch has been serviced in years.  It is a manual wind with sub seconds.  He said he wound the watch and it was working for a couple of days.  Now it does not run though.  The problem with the watch now is that when you wind it, the mainspring doesn't seem to me winding, the crown spins and spins without any increase in tension.  You can hear the clic clicking away so I assume that the keyless works are connected all the way to the ratchet wheel.  So we assumed broken mainspring. 

The unusual thing is that when you pull the crown out into setting position and put any forward motion thus advancing the time or any forward pressure without advancing the time, the watch starts to run.   I'm stumped.  If I assume that the mainspring is broken, how is there any power on the watch and what is this phenomenon of the watch not running in the winding position but running when in the set position with forward motion or pressure on the crown?

Would greatly appreciate your help on this.  

Regards,

Jeffrey

[nickelsilver]

It does sound like a broken mainspring.

 

When you set the time you are slipping a friction clutch that is directly mounted to the center wheel of the watch- which is also what directly receives the power from the mainspring barrel. So when you set the hands forward you are supplying forward power/ motion to the gear train, and this is running the watch. Totally normal.

[VWatchie]

35 minutes ago, nickelsilver said:

When you set the time you are slipping a friction clutch

If of any interest; that "friction clutch" is called the "cannon pinion", and when setting the time its slipping action on the center wheel arbor isn't perfect so it exerts some force on the center wheel which is part of the gear train (as @nickelsilver already explained).

[Nucejoe]

9 hours ago, Jfree said:

The unusual thing is that when you pull the crown out into setting position and put any forward motion thus advancing the time or any forward pressure without advancing the time, the watch starts to run.   

Thats not as bad as my watch, runs backward when put in any backward motion.

[VWatchie]

12 hours ago, Nucejoe said:

Thats not as bad as my watch, runs backward when put in any backward motion.

Ouch!  Too little grease on the center wheel arbor?