Tensioner pulley is locked

2003 MERCEDES BENZ ML320
10,000 MILES • 4WD • AUTOMATIC
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TOMTS
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  • 3 POSTS
Can I unscrew the screw that fastens the pulley, or I need to replace the tensioner? If unscrewing is possible, is it clockwise or counter clockwise direction? Thanks.
Apr 28, 2019 at 12:51 PM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.
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JACOBANDNICKOLAS
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Welcome to 2CarPros.

Honestly, the tensioner needs replaced if it has failed. I believe the bolt you are referring to is just the pulley bolt.
Here are the directions for replacing the tensioner. The attached picture correlates with the directions.

___________________________

AR13.25-P-3200B REMOVE/INSTALL POLY V-BELT TENSIONING DEVICE
Remove/Install Poly-V-belt Tensioning Device


Shown On Engine 112


Picture 1

1 Remove viscous fan (1)
2 Remove fan shroud (2).

NOTE: On Model 163 unscrew the screws at the bottom of the fan shroud.

3 Remove poly-V-belt (3)
4.1Rotate the tensioning pulley (4a) in the anti clockwise direction and lock

NOTE: Lock tensioning pulley with drift or pin (diameter 5 mm).

4.2Rotate the tensioning device at the hexagon (4b) in the anti-clockwise direction and lock

NOTE: Lock tensioning device with a drift or pin (diameter 5 mm).

5 Unscrew the gas-operated spring (5) from the coolant pump

Shock absorber of belt tensioning device at the coolant pump housing - 35 N.m

6 Remove tensioning device (4)

Self-tapping screw of belt tensioner at the timing case cover
- Thread not pre-tapped - 35 N.m
- Thread pre-tapped - 25 N.m

7 Unscrew gas-operated spring (5) from the tensioning device (4)

Shock absorber of belt tensioning device - 25 N.m

8 Install in the reverse order

_____________________

Let me know if this helps.

Take care,
Joe
Apr 28, 2019 at 6:48 PM
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TOMTS
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Thanks Joe for the detailed instructions. They are very helpful. I am curious what could cause the pulley to be locked. Is that a common failure? Thanks again.
Apr 28, 2019 at 10:26 PM
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JACOBANDNICKOLAS
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Welcome back:

The bearing inside which the pulley turns on is most likely bad. Honestly, like any bearing, they have a certain lifespan. With that, I have to say it is common and nothing out of the ordinary.

By the way, you are very welcome. Let me know if you need help and if you get it done.

Take care,
Joe
Apr 29, 2019 at 6:19 PM
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TOMTS
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Thanks for the explanation. Because this happened within a few days after the alignment work of my car and I never heard any abnormal noise from the belt before, I was trying to blame it to be caused by the alignment work. I guess it might be just a coincidence in time.

Yes, I was able to replace the tensioner with a new one. The driving belt works fine now. Thanks for the instructions. Because I don’t have the tools to remove the fan, I skipped the fan removing step. The space is really tight, but I managed to get the job done.

Thanks.
Tom
Apr 29, 2019 at 10:37 PM
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JACOBANDNICKOLAS
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Not a problem, Tom. I'm glad you got it replaced. As far as an alignment, in all honesty, I don't see any correlation. They just go bad.

Please feel free to come back anytime you have questions.

Take care,
Joe
Apr 30, 2019 at 6:23 PM