driver belt tensioner
 

mine shake like mothaflocker. i took it to the dealer they said it's normal. is it true?:sigh:

Mine shakes too.

mine shake like it's about to jump off :mad0260:

It's an automatic tensioner. Essentially the pulley is mounted to a spring-loaded arm. As the belt changes tension due to variances in the load of the engine, alternator, waterpump, and A/C compressor, it will move to keep the belt at the proper tension. So some movement is normal.

Now if it's moving enough that you can see the belt jumping around between the other pulleys, then there's something wrong and it should be replaced.