Nikon F3 weird mirror problem..please help!!

[Gumby]

While true, sticky foam doesn't affect the mirror travel after the adhesion releases. This occurs after a very short amount of travel when it's the main mirror's foam. It possibly could impact the travel over a slightly greater portion of travel range when it is the secondary mirror that has the issue, but still, once the foam releases the mirror travel should be brisk.

If the mirror return is "limp" (read: falling only due to gravity) or slow/sluggish over the whole range then the mirror foam is not the primary cause.

I once had a camera with a sluggish mirror return (Ricoh, not Nikon) that was indirectly caused by mirror foam. The foam turned to goo and got into the return mechanism making it slow to return. Once cleaned out everything worked fine.

 

[nikon_sam]

Cal and Sam,
a waste of time in this case because of the secondary mirror!! lift the mirror up and before the main mirror contacts the foam strip the secondary has probably already stuck to the rear of the main. j

Good point...you can still lift up the mirror to a point where the secondary mirror isn't closed and see if the mirror snaps back down...if it doesn't go back to it's resting point it might be the spring...
Remove the lens and shake the camera while holding it upside down...the mirror should not move if the spring is good...

 

[Dwig]

I once had a camera with a sluggish mirror return (Ricoh, not Nikon) that was indirectly caused by mirror foam. The foam turned to goo and got into the return mechanism making it slow to return. Once cleaned out everything worked fine.

If the foam decomposes to the point that it partially liquifies, it can migrate to the mirror's pivots, hinges, and elsewhere. This could lead to sluggish action throughout the mirror's travel range. If this has happened, the issue would definitely no longer be a simple foam replacement issue. The whole mirror mechanism may need significant cleaning and relube, not a DIY situation.