[Brakes] Strange ABS problem after drive-shaft replacement

[Midpat]

Hi all
Ive just replaced the driveshafts, drop links and track rod ends on my 2005 MK2 2.0 hdi van, all went well, or so I thought.

Now if i drive down the road gently brakes are fine. If I brake sharp the abs locks the wheels like Starsky and Hutch, if I loose the pedal off then reapply the brakes then the pedal is hard as rock (all the way up wont go down) and i have no brakes.

I have to stop the van (clicking noise heard from the front) , when the van stops the pedal goes down with a clunk and brakes operate normally. Any ideas please?