Grant,
I've got a couple other Singers I'm gonna check to see if this might be parts of their problems too.
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I checked my Dressmaker 7000 yesterday. The gears are in good shape and undamaged. I ran it for quite a while but could not figure out why it surges when a cam is in. I compared my machine to the pics you sent me and they are the same. I even took the spring off the cam follower and used my finger to push the follower to the cam. It still surged.
So I put a stronger motor on it. No difference.
I am officially stumped on this one. Looks like it just might have to go to the LSMG.
Joe