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Pelican Technical Article:

Idler Pulley Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$30 to $150

Talent:

**

Tools:

E10, E12 Torx sockets

Applicable Models:

Mercedes-Benz C350 (2008-15)
Mercedes-Benz GLK350 (2010-15)

Parts Required:

Tensioners

Hot Tip:

Don't throw out your old hardware

Performance Gain:

Quiet Engine

Complementary Modification:

New Tensioner

The idler or guide pulleys in the W204 C350 sits above and to the left of the coolant pump pulley and are high tension stress points in the belt system on your car. It can fail over time and usually will let you know it is going bad by starting to make a whining sound. If the pulley starts whining you should replace it right away, as it will only get worse and then fail completely. While you are performing this work you should also check your V-belt for wear, cracking, fraying, delaminating and drying out. If your belt shows any of these signs you should replace it. I recommend you buy two belts and always keep an extra one in the car. You don't want to be stranded on the side of the road for the lack of a spare drive belt.

Replacing the idler pulleys on your Mercedes-Benz W204 is one of the easier jobs you will do. You should be able to do it in well less than two hours. It is a great starter project if you are just beginning to DIY or 'Do It Yourself' on your car.

Let the car cool so you don't have to work around a hot engine.

You need to remove the front engine cover (red arrow) and the air ducts (yellow arrows) to replace the idler pulleys so please see our article on engine cover removal for additional assistance.
Figure 1

You need to remove the front engine cover (red arrow) and the air ducts (yellow arrows) to replace the idler pulleys so please see our article on engine cover removal for additional assistance.

There are two idler pulleys on the C350, one smooth (yellow arrow) and one ridged (red arrow).
Figure 2

There are two idler pulleys on the C350, one smooth (yellow arrow) and one ridged (red arrow). The smooth pulley uses an E10 bolt and the ridged pulley uses an E12 bolt.

You will need to remove the Poly-V or drive belt to replace the pulleys; please see our article on replacing your drive belt for additional information.
Figure 3

You will need to remove the Poly-V or drive belt to replace the pulleys; please see our article on replacing your drive belt for additional information.

Both pulleys use E-Torx bolts.
Figure 4

Both pulleys use E-Torx bolts. Make sure you have the right sockets, and do not try and replace the pulleys without the proper tools.

The smooth idler pulley uses an E10 bolt (red arrow).
Figure 5

The smooth idler pulley uses an E10 bolt (red arrow). If you use the proper socket, removing the bolt is easy.

Don't throw out the old hardware until you see what comes with the new pulleys.
Figure 6

Don't throw out the old hardware until you see what comes with the new pulleys. These bolts are micro-encapsulated and considered single use only by Mercedes Benz.

Change the socket to an E12 Torx and remove the single bolt holding the ridged pulley in place (red arrow).
Figure 7

Change the socket to an E12 Torx and remove the single bolt holding the ridged pulley in place (red arrow).

Again, don't throw out the old hardware until you see what comes with the new pulleys.
Figure 8

Again, don't throw out the old hardware until you see what comes with the new pulleys. These bolts are micro-encapsulated and considered single use only by Mercedes Benz.

Always check the mounting area for the pulleys for any damage and clean the area to give you a good flat and flush mounting surface.
Figure 9

Always check the mounting area for the pulleys for any damage and clean the area to give you a good flat and flush mounting surface. Installation is the reverse of removal.

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