I´m not 100% sure of what "juddering" means, (I´m from Sweden) but I think you mean the abs is trigged but not to 100%.
My problem was (855 -96)that sometimes when I stopped the car, just before it completely stopped, the abs was ticking for a second or two. This happend very intermittently. My workshop knew about the problem and replaced the abs-sensors
on the front wheels and reworked the wireing between the sensors and the controlbox. (I don´t think it was the sensors that failed but the wireing between sensors and controlbox). This was covered by my insurance against motordamages.