If you pull down on the lever slightly,get someone to pump brake,you should feel movement there,if not it's probably seized,quite important to get them adjusted correctly or back brakes could grab on when unladen,think there was a diagram in engine compartment detailing adjustment and a rolling road would help too if there are no measurements available,if I remember I used to adjust the long spring until it lowered the long arm slightly reducing braking force to rear brakes if there was no load in the back,come MOT time you could ask the tester of brake readings and if they are a decent sort would help in adjusting the valve correctly if it needs it, good luck.
cdc
February 2017