Tensioner pulley is locked

Tiny
TOMTS
  • MEMBER
  • 2003 MERCEDES BENZ ML320
  • 4WD
  • AUTOMATIC
  • 10,000 MILES
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.
Sunday, April 28th, 2019 AT 12:51 PM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
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
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Sunday, April 28th, 2019 AT 6:48 PM
Tiny
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.
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Sunday, April 28th, 2019 AT 10:26 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
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
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Monday, April 29th, 2019 AT 6:19 PM
Tiny
TOMTS
  • MEMBER
  • 3 POSTS
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
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Monday, April 29th, 2019 AT 10:37 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
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
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Tuesday, April 30th, 2019 AT 6:23 PM

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