I will put my two cents in here about the cams. I picked up a 778 Touch and Sew a couple of weeks ago. It uses the black colored Top Hat type cams. Strange thing is, it has to have disk #0 in the machine to do a ZZ stitch. If it is not in there it will just sew a straight stitch. Mine didn't come with disk #0. It also uses the white colored Flexi Disks.
The other odd thing is, it had a smooth feed dog that was black. The black is because it is rubber. It was old, smooth and hard. Needless to say it no longer worked. It just slid on the fabric. I had to replace that one with an all metal one.
Next time I pick one up I will know to look at these two things as well as the gears.
One final thing on the gears. I recently read that the white gears were the original part. The black ones are the replacement part. So, if this is true, when you look at a machine and it has black gears in it, they were replaced. Can anyone confirm this?
Thanks.
~Grant~