I'd check to make sure the pulley is not out of round or bent.

Tzung-Horng Yang wrote:

>  Hi Volks, I am back to California (San Diego) and am glad to join to this
> list again. I have a rare (?) problem about my alternator cradle bracket.
> In late July while I was still in Denver, CO, I had a noise coming from
> the engine compartment and the van vibrated pretty badly. The VW dealer
> mechanics found the barckets of the alternator were broken and replaced
> them. Yesterday, the same problem happened. Strange enough, I looked
> through all the repairing records, and found previous owner had done the
> same repairment once (only the cradle barcket not the support one) at
> about 60 K (it is 86 K now). I searched the archives and find no clues. I
> remember the old German mechanics at VW dealer in Denver told me that he
> has not seen this problem before (actually I had to do special order for
> the barckets). Does anyone have any similar problem occur to them or any
> idea what might be wrong with my car? Thank you for all your help. Tzung
> Yang 1990 VW Carat Vanagon

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