DFac Boy

Greetings,

I recently replaced the serpentine belt, idler pulley, and belt tensioner on my car for preventive maintenance. My C55 has only 52,900 miles but I want to ensure high reliability and avoid breakdowns. I used only OEM parts purchased from a mix of vendors, Amazon, AutohausAZ, and MBParts World.

I started by removing the idler pulley cover using a small pick. If you are particular about under hood appearances you may want to add a replacement ($3.20) to your bill of materials. Mine was faded so I replaced it.




Once the cover is off, you will have access to the idler pulley bolt which takes a T50 Torx bit. I removed the pulley and installed a new one ($18), tightening the bolt to 15 ft-lbs.



Next, using a 17mm socket on a breaker bar, I turned the bolt head on the belt tensioner counterclockwise until I could install a nail in the designed recess to hold it in that position. Please see your replacement tensioner to understand this requirement. In my case, I did this from underneath the car (after jacking it up). I now removed the belt. The belt tensioner on my car was secured with two bolts which took a T45 Torx bit. I installed the new tensioner ($98) and tightened the bolts to 18 lbs-ft.



Finally, I installed the new belt ($21) and the learning moment for me on this was that you should run it around all the pulleys except the water pump pulley. The lack of a lip on the water pump pulley lets you slide the new tight belt on under tension. Once the belt is properly in place, go back and remove the pin/drift from the new tensioner by releasing tension first (with 17mm bolt head on the tensioner turned CCW)



Working near the fan shroud can tear up your forearms a bit so try to wear long sleeves or protectors. The whole job took about an hour and a quarter. I wasn't racing against the clock.

Rahulio1975280C

Awesome write up, I just bought a new drive belt, but now I will source the idler pulley and knock them both out at the same time.

Thank you!

PelicanParts.com

Great DIY! We too have a DIY write up on the idler puller replacement. Fun job right? If you do any other DIY content that you don't see listed on our articles let us know! We'd love to cross reference it.

-Luccia

DFac Boy

Sure thing, Luccia - I have used your DIYs before. Great format and excellent photographs on yours! Thanks.