Any know failure with our pullies. I have a 2012 GL550 with 46k puley came apart no warming what so ever belt was good. replaced all pullies and tensioner. Hardest part was to route the belt and no diagram anywhere on the truck. Thank too an Ebay s550 motor forsale I was able route it.
I am thinking same pullies for the AMGs and being over 50k should I change them out. Are their metal replacement.

 

Yes, I installed a set of billet aluminum pulleys from UPD, still on sale. They are of decent quality. The original OEM pulleys are very good too; much better than my previous W211 AMG. Four of the OEM pulleys are plastic, and 1 is metal. OEM bearings are sealed NSK (Poland) in small pulleys, and a very strong NBR+Fe in the large one. After 57K miles, the original bearings had minimal play, reasonable grease, and I felt could last another 30K easily. Yes, it makes sense to change the serpentine belt. There are 2 variations of the M157 belt, and so you shall pay attention to your VIN/date.

 

Yes they fail but that is early