Hiya Katie, remove inner hangle and door card. With the door shut remove center track cover (2 philips screws - one under the cover on either end) and knock it gently upwards and out of it's channel ... watch that paint !! Now obtain a milk crate or similar non mekal object about 18" tall with a rag on it to stop the paint being damaged and stable enough so's it doesn't move (to rest the
quite heavy but more cumbersome sliding door on). Now with the door about 2" open watching the centre roller you'll see a slightly wider opening on the rail, lift and persuade the centre arm/rollers assembly of the door out towards you out of it's channel and now with the slider (*sniggers*) fully open (i.e. towards the back of the van) rest it on the crate/block about 12" away from the van body.
There are 3 bolts and washers which secure the centre arm/rollers assy to the door (one hidden in a reccess in the door itself), using a 13mm socket on an extension slacken (do not remove) these enough to move the door on it's screws towards the front of the van (possibly only 5 or 10mm or so may be enough) re-tighten the 3 bolts, refit the door (re-fitting is the reversal of removal as Haynes always say

) and test, looking at the gap around the door should be a good, general guide. Then replace the cover and the door card.
Ian
