I have had numerous cases of Accumates locking open. I have never had
this problem with the Scale Accumates because the scale draft gear box
is too narrow to allow the coupler halves to separate far enough to
lock.

I have seen this on KD 5s as well. In this case it is caused by wear
on the knuckle stop on the side of the coupler. The stop gets worn down
sufficiently to allow the heel of the knuckle to slide slightly over it
and either jam or stick very briefly. I can often fix this by using
very fine needle nose pliers to slightly bend the bottom corner of the
heel on the knuckle inward so that it once again will hit the stop
firmly and not slide past it.


regards,

Andy Miller