I have a 3 phase Yale 1/2 ton hoist. It has an electric brake with a
solenoid, whose job is to pull away the brake lever when 230VAC is
supplied to it.

The problem is that it does not do it. Instead of steadily pulling
away, it constantly jerks the lever, but never far enough to the end
point where it is supposed to be pulled away. So, the brake is not
disengaged as the hoist operates. I am glad that I noticed that.

I tried pulling on the lever by hand when the solenoid was engaged. I
noticed that if I help the solenoid and pull away the lever to the
end, jerking stops completely, but if I slowly let go of the lever and
it returns to the brake position, jerking resumes.

I am thinking that perhaps this solenoid has two separate coils,
pulling and holding one, and the holding one is not working or not
engaging?

Any idea?

thanks