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John, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 9176
Experience:  I have worked in vehicle driveability for more than 30 years.
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Just changed the IDLER pulley on my ML350 2003. Any instructions

Resolved Question:

Just changed the IDLER pulley on my ML350 2003. Any instructions on getting the belt back on? I would assume to lossen the alternator (Located on the bottom left standing in front of the truck). But it appears if I loosen the 2 bolts, I can't see how it'll slide forward to get the belt to wrap around. Am I thinking incorrectly?
Submitted: 6 years ago.
Category: Mercedes
Expert:  John replied 6 years ago.


Here are some instructions that should helps you.The belt tensioner is the part that applies the correct tension to the belt.


The belt is tensioned automatically. If the belt is slipping, either the belt has stretched beyond its serviceable limit or the tensioner is faulty.

Drive Belt Routings

Click image to see an enlarged view250" height="225"/>

Fig. Accessory drive belt routing-all engines

Click image to see an enlarged view

Fig. Accessory serpentine belt routing-Mercedes-Benz 3.2L engine


Inspect the drive belt for signs of glazing or cracking. A glazed belt will be perfectly smooth from slippage, while a good belt will have a slight texture of fabric visible. Cracks will usually start at the inner edge of the belt and run outward. All worn or damaged drive belts should be replaced immediately.

Removal & Installation

  1. Before servicing the vehicle, refer to the Precautions Section.
  2. Remove the cooling fan and fan shroud.
  3. Using a breaker bar and appropriate sized Torx socket (or appropriate drive belt removal tool), relieve the belt tension by rotating the tensioner.
  4. Remove the belt from the pulleys.
  5. Installation is the reverse of removal. Be sure to follow the belt routing diagram.

    Click image to see an enlarged view

    Fig. Exploded view of the drive belt removal

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