The original pulley was stamped steel. It was susceptible to going out of round and out of balance if belts were pried on and off too vigorously.
(picture of original pulley needed)
In addition, since the intermediate shaft runs at half engine speed the alternator would have run slowly except that a very small pulley was fitted to the alternators. Even so, the alternator runs slowly compared those fitted in other cars.
(picture of small alternator pulley needed)
Citroen USA developed and tested several types of replacement pulley to compensate for these problems. A solid steel one was tried but proved too heavy and thus wore the pump bearings out. The best choice was solid aluminum, which incorporates a larger radius groove for the alternator (dimensions needed).
(pictures of new pulley needed, ideally one side-by-side with old pulley, and one installed)
This weighs about the same as the stamped steel pulley, but turns the alternator (x) % faster.
As developed by Citroen USA, it uses a (x) mm belt rather than the standard (x) mm belt. Althought it is harder to get tension on it (due to shorter distance between pulleys) slippage is not a problem.
(As of 8/08, David Hume at Excelsior Motors has several of these available.)