My Kenmore 158.1940 has a feed dog drop. It doesn't work. When I was in North Carolina, I tried to fiddle with it but ended up not fixing it AND altering the feed dog height in the process. Luckily Alice had her machine along and I used it for a comparison and figured out what I had done.
OK I hate it when anyone calls a machine part gizmo. I am off to look up on Sears Parts Direct the proper names of these things. http://www.searspartsdirect.com/partsdirect/index.action It is call a center.
The Center does pull back from its housing when the feed knob is depressed. BUT the feed dogs don't drop because the gizmo (I can't find the real part name on the parts chart. You can try, I can't figure it out) the Center fits into doesn't move.
So I tried to move it. I loosened screw A and that didn't do anything. Well, that's not true. Loosening screw A screwed up the feed dog height because it allows for just such an adjustment. I readjusted screw A and raised the feed dog height and proceeded to make more hats.
I like this machine. It is back in the shop now awaiting appropriate feed dog attention. I will get the feed dogs to drop. It is just a matter of heat, Tri flow and cleaning. Maybe this weekend I will do it.