What could be wrong with Gruen caliber 385

Hi All,

My buddy at work just got his grandfathers old 1947 Gruen very thin watch for Christmas. It has the caliber 385, manual wind sub seconds movement in it. I don't think the watch has been serviced in years. He said he wound the watch and it was working for a couple of days. Not a good idea, I know. He brought the watch to show me and and said the watch does not run anymore. 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 working and the winding pinion is engaging the crown wheel 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? Also feels too tight when advancing time?

Would greatly appreciate your help on this.

Regards,

Jeffrey

There is friction in the system. You advancing the time gives the watch just enough power to run.

Even when the cannon pinion is not sliding on the center wheel arbor, when just holding forward pressure, watch runs. This can happen with no power in the barrel? Thanks

Sure, because the barrel drives the hour wheel, and when you're manually moving the hour wheel....

Thanks so much. So not such a mystery after all. Should I suggest to my friend that he just needs to get his watch serviced and will probably just need a new mainspring? Could something else like the barrel arbor be the culprit or most probably a broken spring?

This still seems a little strange to me because the watch runs even if you are not turning the crown but only have forward pressure on it?

Again, you're putting force on the barrel using the winding system. Perfectly normal and explainable.

OK. Great! and Thank you!

Mind you, this is just enough force to cause the escapement to move... but not enough to actually keep time.

That makes sense. So probably just a broken mainspring?

That is the obvious answer but that watch likely hasn't been serviced in a very long time, so it needs a full service regardless... and most watchmakers will replace a mainspring as a matter of course regardless, especially the old ones.