So having looked at your profile you place yourself in Manchester yet you have the user name hebden endomorph.
So are you actually from Hebden Bridge. If so then the obvious next question is, "Social worker or teacher?"
In my rush to mock you because of your user name I almost missed what it was you said you had delivered. A Dandy Dash! Well what an exclusive club of 4 you are in. If you bought it from the long term ad in The Dandy Owners club then this is still the only one I have actually heard about. If not yours is the second. [You must be registered and logged in to see this link.]
Whichever it is could you please send some photos. "We Love Photos Here"
All in all your Dandy is a very rare beast.
What attracted you to this model in particular?
Generally agreeing with navver any final adjustment must be made with the adjusters at the back of the hub. Though I'm not sure why the damper being stiff would hold the brakes on. Greasing the damper is always a good idea too.
We are always glad to help but if you need information in a hurry try using the search option offered at the top. Entering the word "Brakes" into the box would have given several options with this one of the most replied to. [You must be registered and logged in to see this link.]
The braking system is a bit of a hotch potch with an AL-KO overrun hitch and Knott brakes. The simple printed sheet below is the guide included with Dandys when sold through the Knott guides explain more and offer help in fault finding.
Warm hubs are either sticking brakes or worn bearings and the Knott guide covers both. It must be read with some latitude though e.g. The Knott guide mentions the hand brake going "over centre" and self applying. The AL-KO hitch and handbrake is not (ouch) of this type and just has the spring as an energy store.[You must be registered and logged in to see this image.]