THE SQUEAK HAS NOTHING TO DO WITH SHUTTER TIMING. NADA,ZIP,ZERO, ZILCH!
Shutter isn't released until the mirror reaches the top of it's travel.
I'm not entirely sure of the specific relationship. I have heard there is a link to shutter speeds. Something about the speed of the mirror impacting the speed of the shutter if you let it go too long, screwing up (over-exposing) 1/1000 and 1/500 speeds. So, yes... It is the mirror gear that's making the noise, but it isn't isolated.
Also, the problem is not only one of dried out lube, but if you read the link below you'll see it often is a wearing on the bearing that causes the squeal.
I guess if it's that bad, I kind of agree with David Marsh here (from a while back) where he states there are other problems brewing; it's just the mirror that's screaming for attention.
I could just be barking up a wrong tree, I freely admit. However it concerned me with regards to my AE-1P and keeping it doing what I wanted it to do.
(I'm not necessarily debating the issue, just clarifying where I came from when I did it)
Canon AE-1P 35mm | 50mm/f1.8 FDn | 28mm/2.8 FD | 70-200mm/f4-5 FD | 35-70mm/F2.8-3.5 Sigma FD
...at the end of the day it seems silly to spend say £60 for a CLA on an ordinary A series camera when for £60 you can buy a t90 body (of course with no EEEE in the viewfinder )
The shutter speeds are not affected by the mirror! 1000sec to 14 days. The mirror does only one thing. It releases the 1st shutter curtain. period.
When the mirror reaches the limit of it's travel at the top of the mirror cage, it strikes the shutter release lever. This is not affected by the speed at which the mirror strikes the lever as long as it has enough force to move the lever. Once the release lever is struck it releases the 1st curtain, the 2nd curtain is released after the interval required by shutter speed selected.
If you could release the shutter release lever with a tooth pick, it would work accurately too.