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Accessory Drive Belt Tensioner Replacement
 
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Pelican Technical Article:

Accessory Drive Belt Tensioner Replacement

Kerry Jonsson

Time:

1 hour1 hr

Tab:

$150

Talent:

**

Tools:

17mm deep socket or socket with extension, T10 internal Torx socket

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Accessory drive belt tensioner

Hot Tip:

Take a photo of the accessory drive belt routing

Performance Gain:

Stop belt squealing

Complementary Modification:

Change the accessory drive belt while you're at it

In order to operate many of the accessories we take for granted on our car we need to understand that they need a power source. Our air conditioning system needs a compressor to be spun to generate the necessary pressures for the system to work. The power steering pump needs mechanical power to generate the hydraulic pressures for the power steering gear. Your alternator needs mechanical power to spin the rotor inside of it. This is necessary to generate the electrical power the car needs while it is running. Finally the water pump needs mechanical power to spin the impeller and circulate the coolant around the block and cylinder heads.

The crankshaft pulley supplies mechanical energy or power. The engine's energy turns the crankshaft, which is then sent through the driveline to propel the car. The front crankshaft pulley "steals" power from the engine to rotate the accessory drive belt. This belt turns pulleys for the systems mentioned earlier. Now in order for this single serpentine belt to work it needs to be tight on the pulleys. This means the belt is going to need tension on it to properly grip the pulleys. An accessory drive belt tensioner provides the appropriate amount of tension on the drive belt. This accessory drive belt tensioner is spring loaded so it can always apply tension to the belt, even as the accessory drive belt stretches out over time. However, over time the belt may stretch too much or the spring in the accessory drive belt tensioner can weaken. This means the accessory drive belt tensioner will not be able to provide the necessary tension to the accessory drive belt and it may allow the pulleys to slip. This is usually accompanied by a squealing noise as the belt slips over the pulleys. This also means the accessories themselves may not have the necessary mechanical power to operate and you may lose charging system voltage, low coolant circulation, no power steering assist and poor AC output. In this tech article we will go over how to change your accessory drive belt tensioner.

This picture illustrates the front left side of the engine compartment.
Figure 1

This picture illustrates the front left side of the engine compartment. Using a 17mm socket with ratchet, rotate the tensioner lug in a counterclockwise direction to relieve tension on the accessory drive belt.

Then remove the accessory drive belt from the tensioner pulley in the direction of the green arrow.
Figure 2

Then remove the accessory drive belt from the tensioner pulley in the direction of the green arrow.

Using a T10 Torx socket remove the right mounting fastener (green arrow).
Figure 3

Using a T10 Torx socket remove the right mounting fastener (green arrow).

Next, remove the T10 Torx left side mounting fastener (green arrow).
Figure 4

Next, remove the T10 Torx left side mounting fastener (green arrow). You do not need to release the tension on the accessory drive belt tensioner to loosen and remove this fastener. We have done so to allow a clear view of the left side fastener.

Pull the accessory drive belt tensioner away from the engine.
Figure 5

Pull the accessory drive belt tensioner away from the engine. Installation is the reverse of the removal procedures. Fit the accessory drive belt tensioner into the engine block. Install the two fasteners and tighten them. Route the accessory drive belt around the pulleys. Start at the alternator and then wrap in around the water pump. Then pass it over and around the tensioner onto the crankshaft pulley. Now wrap it underneath the AC compressor pulley and around the power steering pump pulley. Finally, hold the accessory drive belt tensioner in the counter clockwise position and fit the belt over the idler pulley. Release the accessory drive belt tensioner and it will tighten down on the belt. Make sure the belt is properly seated in each pulley and start the car. Make sure the belt does not vibrate excessively and does not make any noise.

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Comments and Suggestions:
E 55 V8 KOMPRESSOR Comments: Works for all w211 except E55 / E63
You want access the tensioner from under the car or remove radiator fan first wich is advisable
June 14, 2016
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
SuperChargedE55V8W211 Comments: How can you tell if the tensioner is worn besides of course worn and noisy nearings. I MEAN tension howndo you check that?
May 17, 2016
  Followup from the Pelican Staff: If there is chain slap or movement, you can assume the tensioner is faulty. Some manufacturers have tensioner preload tools, where you can preload the chain, then check slack. That is a good way to confirm the rest of the components are OK, confirming the tensioner is the issue. - Nick at Pelican Parts  

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