about the alternarors on a vauxhall astra dti, my mum phoned me before to say her battery light had came on and the power steering had gone very hard to use, so initially i thought it had maybe threw a belt off but on closer inspection the belt is still on but theres a part on the alternator that looks like it should be spinning but it isnt, something like a centrifugal clutch on the end of it. so basically does anyone know about these and can they be fixed or is it a new one. i seem to remember somewhere that these alternators cost about £400 to replace, cos they also run the power steering etc. any help appreciated

Thanks Sean.