I understand that my 94 216 cabriolet automatic has a lock up system on the torque converter. I am new to Rover ownership but have Cavaliers of the same period and they lock at 56mph. What speed does the lock up kick in? If it isn't kicking in is the solenoid inside or outside the box? Hopefully I won't need one but are there specialists that work on these boxes? The car has done 87k miles with full service history. I'm in Bournemouth.

I don't think there is a solenoid, a [now] old fashioned system relies on fluid pressure at higher speeds to lock the T.Q. My Merc' improved remarkably in this respect after a fluid change.
Thinking about it there will be a solenoid to prevent lock up in lower gears. Mine [Rover 216 auto] did seem vey much like a slush box compared to a 5 speed Merc' though.

The workshop manual is as helpful as Haynes; you need a copy of AKM 6501 'L4 Auto Box O/haul'

Thanks very much. I am covid positive at the moment but as soon as I am clear I will get the fluid changed as well as hunting for that manual.