I have seen the test of the solenoid on YouTube made by Moss " Overdrive Transmission - how to test the Overdrive solenoid". In this video it seems like there is a spring inbetween the plunger and the bottom of cylinder. In both of mine solenoids, there are no springs inside.
My car is a 1964 mk2 chassis 179733DN. 1. the original A- type from 1964 sitting on gearbox nr. GBN 78434JS and 2. a Compact A-type sitting on the gearbox nr. KCN 2689 from 1969 (from a jag. 240).
Can anybody tell me please it the springs are missing or not? When I look into SNG Barratt - there are no spring included in the part. Please help me out here. :-)

 

I don't think there's any need for a spring in the solenoid. The solenoid moves the oil pump plunger against a return spring to apply oil pressure and engage o/d. When the solenoid isn't carrying current, the return spring takes the whole mechanism, solenoid included, back to the disengaged position.

 

Springs no longer used. Magnetic field does all the holding in place on the solenoid.