Many of these cars have a split pulley somewhere (with shims; like a beetle generator pulley!).  One of my MK2's was like that; it wouldn't come apart without taking out the pulley allen bolts that thread into the hub.

HTH,

Mike B. 
  ----- Original Message ----- 
  From: pdooley 
  To: vanagon@GERRY.VANAGON.COM 
  Sent: Friday, September 25, 2009 4:57 PM
  Subject: Re: Friday: Need help with Jetta, final request

  The MK2's use a complicated PS bracket with a bolt practically hidden in the
  bracket.  This bolt goes through the bracket and tightens into the back side
  of the PS pump body.
  Loosen this bolt and the PS pump will move a decent amount.
  Thank goodness for the later serp setups, these old Vbelt models are a PITA.

  -----Original Message-----
  From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
  Jim Felder
  Sent: Friday, September 25, 2009 4:29 PM
  To: vanagon@GERRY.VANAGON.COM
  Subject: Friday: Need help with Jetta, final request

  Folks, if someone can't help me out with a belt change problem on my
  91 diesel Jetta, I'm going to have it towed to a shop and for the
  first time in many years actually pay someone to do something as
  simple as changing and adjusting the waterpump and AC belts.

  I have the bentley for the car. Worse than useless.

  I have been to the library to look it up in Mitchell's. Nothing.

  I have googled every permutation of words describing what I want to do
  for two weeks. Nothing.

  I joined every Jetta list on the internet. Nothing at all.

  I have removed or loosened every nut and bolt on the alternator,
  compressor and PS pump that I can find. Alternator belt's off, I get
  that. I can move the AC compressor about an eighth of an inch, and I
  have a setup just about like it to look at for reference on another
  engine, so I know I've gotten everything loose there. I cannot move
  the PS pump a thousandth of an inch without, as far as I can tell,
  removing every bracket and adjuster holding it to the block and I
  still don't think that would solve the adjustment problem at all.

  So, I'm going to ask here, at the only place I know of to find out, in
  case someone on the list has done it: How do you replace and adjust
  the alternator and AC belt on a 1991 diesel Jetta?

  Thanks,

  Jim