Hi Everyone,

I drive a 2008 CLS550 that just reached 110k. This week the serpentine belt snapped and the idler pulley went with it. As this job doesn’t require a shop to repair it I bought the parts and replaced the belt and pulley. This was Friday night. There was a little ticking/squeaking sound coming from that area but I figured it might be something that needs to be worked out. When I got home that sounds was gone. Yesterday i drove to the store and dreadfully lost powering steering again. Once I got the car to a parking lot I popped the hood and found that the belt had fallen off. Does anyone know why that would happen? I don’t believe it has anything to do with the tensioner as it was extremely hard to get the belt back on the car(thankfully I had a spare belt in the car as this incident bent the Continental belt that I originally bought which made it impossible to use it again) It definitely provides enough tension to keep the belt in place.

Now thinking back to Thursday night, the idler pulley didn’t seem right as I was putting it into place. It seemed like it was going in place but it wasn’t tightening. No torque.I also noticed when my girlfriend started the car that it kind of slanted down a bit as the belt started spinning.

I checked on the MB website for the idler pulley part and I noticed the bolt on their site is significantly different than the bolt that came with this pulley. It seems longer and has different placement of the groves. I’m going to check the part numbers today to make sure the part is correct.

Does anyone one have any advice or has anyone had this happen to them?