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Replacing Your Mercedes Belt Tensioner
 
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Pelican Technical Article:

Replacing Your Mercedes Belt Tensioner

Steve Vernon

Time:

1 hour1 hr

Tab:

$100

Talent:

*

Tools:

E10, E12 Torx driver

Applicable Models:

Mercedes-Benz ML320 (1998-03)
Mercedes-Benz W203 (2001-07)

Parts Required:

New belt tensioner and V-belt

Hot Tip:

Don't work on a hot engine

Performance Gain:

Wont leave you stranded at the side of the road

Complementary Modification:

New belt

The V-belt tensioner provides a constant tension on the belt which is needed to run all of the engine accessories. Over time the tensioner can fail to maintain the proper tension and the belt will start to slip. If this happens it will usually make a squealing noise. The tensioner can also fail by the bearing wearing out - this will cause the belt to wear unevenly and fray along the edges. You should check your tensioner and V-belt every six months for wear, cracking, fraying, delaminating and drying out. If the tensioner is loose or you can wiggle it or if your belt shows any of these signs you should replace them. I recommend you always replacing the belt when replacing the tensioner and 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.

The belt on our project car was one of the worse looking belts I have ever seen on a running car. The under side of the belt was beginning to get shinny which is a sign the tensioner is loosing its ability to hold the belt at the proper tension. If your belt looks like the one pictured here you should seriously change it ASAP.

Replacing the belt tensioner on your Mercedes-Benz W203 is a relatively easy job. You should be able to do it in an hour and 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. With the hood open you need is an E10 (reverse Torx socket) and driver. Locate the tensioner and using the Torx driver turn the nut on the wheel counter-clockwise 45 degrees. You can now slip the belt off the tensioner.

To remove the tensioner you will need to lock it into the open position. Turn the tensioner wheel counter-clockwise and insert a retaining pin between the rotating part and the tensioner base. If you do not have a retaining pin you can use a 5mm Allen key. It is easier job to install the pin after you have removed the belt as it can be a tight fit getting the pin in while the belt is in the way.

With the tensioner locked in the release position you can see the two E12 bolts holding the tensioner to the block. Use an extension to get at the lower one and take care not to knock out the retaining pin while removing it.

The new tensioner will come locked with a retaining pin in the loose position. Make sure it fits flush to the block or it will "throw" the belt after you install it and start the engine.

There is a picture below that shows you the routing of the belt that you can use to install the new one.

Installation is the reverse of removal. Take care to make sure the belt is properly seated on all the pulleys, follows the right path.

You should check your V-belt every six months for wear, cracking, fraying, delaminating and drying out.
Figure 1

You should check your V-belt every six months for wear, cracking, fraying, delaminating and drying out. If your belt shows any of these signs you should replace it. The belt on our project car was one of the worse looking belts I have ever seen on a running car. If your belt looks like the one pictured here (red arrow) you should seriously change it ASAP.

Locate the tensioner and using the Torx driver turn it counter-clockwise 45 degrees.
Figure 2

Locate the tensioner and using the Torx driver turn it counter-clockwise 45 degrees. You can now slip the belt off the tensioner and install the new one.

You can also lock the tensioner into the open position if you need both hands to install the new belt.
Figure 3

You can also lock the tensioner into the open position if you need both hands to install the new belt. Turn the tensioner all the way counter-clockwise and insert a retaining pin between the rotating part and the tensioner base. If you do not have a retaining pin you can use a 5mm Allen.

With the tensioner locked in the release position (yellow arrow) you can see the two E12 bolts (red arrows) holding the tensioner to the block.
Figure 4

With the tensioner locked in the release position (yellow arrow) you can see the two E12 bolts (red arrows) holding the tensioner to the block. Use an extension to get at the lower one and take care not to knock out the retaining pin while removing it.

The new tensioner will come locked with a retaining pin in the loose position, similar to what the 5mm Allen (red arrow) is doing on the old one.
Figure 5

The new tensioner will come locked with a retaining pin in the loose position, similar to what the 5mm Allen (red arrow) is doing on the old one. Make sure it fits flush to the block or it will "throw" the belt after you install it and start the engine.

This is a picture that shows you the routing of the V-belt; the tensioner is shown by the red arrow.
Figure 6

This is a picture that shows you the routing of the V-belt; the tensioner is shown by the red arrow. Note: the front of the car has been removed to give you a better view.

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Comments and Suggestions:
Tony Comments: I am trying to determine if the Drive Belt Idler Pulley [Part# 272 202 10 19] on my 2006 C230 Sport can be replaced. It does not turn freely and there are two sections of the rear flange that have damage. One section can be seen in the photo.
November 23, 2016
  Followup from the Pelican Staff: It should be replaceable. Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
milz Comments: sorry nick the v belt tensioner it has no bolts to it and the back plate and spindle is stuck in there the spring and everything else is out ?
September 15, 2016
  Followup from the Pelican Staff: We don't have a C200 here, on similar models, the tensioner unbolts using a single bolt from behind the timing cover. - Nick at Pelican Parts  
milz Comments: how do i take the tensioner out of my car it has no bolts car is a c200 coupe k 2003
September 15, 2016
  Followup from the Pelican Staff: Which tensioner? - Nick at Pelican Parts  
sis Comments: looking for a diagram for putting on a serpentine belt for a 2001 mercedes benz ml320
August 26, 2016
  Followup from the Pelican Staff: We don't currently have that tech article. If we get a chance to perform the procedure, we will be sure to document it.

I would grab a repair manual. It will have the procedure, special tools and torque specs.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
ugh Comments: where is the guide rail pin located on a 2002 Mercedes benz c-230 kompressor
June 2, 2016
  Followup from the Pelican Staff: Guide rail pin? What are you trying to fix? - Nick at Pelican Parts  
sandra Comments: the year is 2009
February 24, 2016
  Followup from the Pelican Staff: Got it, thanks. - Nick at Pelican Parts  
sandra Comments: need help i knowing the name of the wheel below the tension er a little to the right, the wheel is broken because it freeze up, would like to buy one its a ml 350 benz
February 24, 2016
  Followup from the Pelican Staff: Without seeing a photo I have to guess. Sounds like an idler pulley. Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
john v Comments: I just installed a new belt tensioner on my C32 AMG W203 and got it installed with the 2 bolts tightened and have the belt lined up. when i try to release the tension with the socket wrench on the new tensioner it will not BUDGE so i'm unable to pull out that retaining pin and let the tensioner slide into place on the belt. how much force do you need to apply to a new tensioner????? my old one was like mush and super easy to release
January 28, 2016
  Followup from the Pelican Staff: Just remove the pin. It is automatic and requires no force. It should move on it's own. - Nick at Pelican Parts  
bosslavish Comments: I have a 2002 c200k and I changed the tensioner more than four times, each time i do, the noise stops, and resurfaces after about 24hrs, i removed the drive belt to check for if the engine is silent, and it was silent, I have changed the tensioner shocks also with no result, what can possibly be the problem?
January 16, 2016
  Followup from the Pelican Staff: Possible oil pressure issue. I would start by checking engine oil pressure and condition. - Nick at Pelican Parts  
Jake Comments: I recently had the drive belt snap, which lead me to checking all the pulleys- the tensioner pulley was pretty much ceased up all other pulleys moved smoothly.
I'm seeing that most automotive places sell only the tensioner pulley assembly, but not the pulley separate from the assembly. I have found elsewhere ebay an identical looking pulley. Is is possible to replace just the pulley or is it fixed to the assembly? Is there any reason to replace the entire assembly?

Thank you for the help!
December 10, 2015
  Followup from the Pelican Staff: If not available, you have to replace it as a unit. I can't comment on unknown parts on ebay. - Nick at Pelican Parts  
Ade Comments: C230 compressor 05, belt tensioner have been change three times, but keep making noise after like one week while engine is running and car is stationary on drive, reserve and with A/C on or not. please help
September 23, 2015
  Followup from the Pelican Staff: Possible noise is from a different component. Remove the drive belt and inspect all of the pulleys. - Nick at Pelican Parts  
Bhavan Comments: When I start the car in the morning or after a while when the engine gets cold, I get a rattling sound from the engine component. Wanted to change the Tensioner pulley but just could not extract it out. Found the way from this site and the professionalism enacted herein has been God's sent.
Keep up this excellent motivator.
September 5, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Brian Comments: Call me please 901-453-2459 i need help adjusting my belt ... I put a new alternator on it and changed the belt that came up in the system and it burns the belt up .. How do i loosen the belt please !!!
September 2, 2015
  Followup from the Pelican Staff: What vehicle are you working on? - Nick at Pelican Parts  
abbe Comments: on 97 e320 pully has only one nut and i am afraid it will loosen the pully instea of v-belt
May 29, 2015
  Followup from the Pelican Staff: This article applies to:
Applicable Models:


Mercedes-Benz W203 (2001-07)

What are you trying to repair? I may be able to offer some advice. - Nick at Pelican Parts
 
MB Mick Comments: You could add one more to your list of Applicable Models. I have a 2001 C240 W203, with a tensioner exactly the same. Posts in MBWorld did not show this variant apart from a single comment buried in a thread somewhere. I'm happy to have found your description here.
February 19, 2015
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated. - Nick at Pelican Parts  
joe Comments: NOISE GONE AWAY WOO HOO lol
Nick The belt made the difference! What a difference in craftsmanship! The Continental is OEM and has a etched more I guess addhesivable, Yes I just made that word up lol, smooth side to the belt which stops it from jumping which in turn stops the noise. I would advise everyone not to use an after market belt on German Cars. Save yourself a headache
December 31, 2014
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
joe Comments: actually sry Ken Did not see the pic. Thought you wanted to change the whole tensioner not the pulley
December 29, 2014
  Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
 
joe Comments: ken - the shallow male or Female torx is what you need to remove the tensioner. It is a E-14 I am pretty sure. You usually have to lock the tensioners to get to one of the bolts unless you have the shock absorber type tensioner.
Nick - The sound comes from the tensioner, which I found out from another tech buddy, is probably the cheap ass belt that dayco makes. He told me, after I changed three tensioners one even being a German OEM part, that I need to put a continental belt on it. The after market ones like to jump and make that sound. IM about to do that now. Ill be back
December 29, 2014
  Followup from the Pelican Staff: Thanks for sharing your installation process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 
joe Comments: I did the water pump and a new belt. After I did the belt and test drove it I was hearing a clicking sound in drive and reverse while sitting on the brake. While moving and while in park or neutral it does not happen. So with someone in the vehicle with foot on brake and vehicle in gear, I put a 17mm socket and ratchet on the tensioner and tugged both ways releasing tension and appying more tension and the noise went away while tugging on it. So I determined it was the tensioner. BUT NO!!!!! The noise came back and so I changed it out again. once the car warmed up the noise came back again. I am not buying the bull shit that it is 3 bad tensioners!!!!! do you have any clue about this? Have you come across this problem before?
December 21, 2014
  Followup from the Pelican Staff: I have not. Where is the sound coming from? If you remove the drive belt, does the noise go away? Do not run the engine long with the drive belt removed, Only a few moments as it can overheat and engine damage may occur. - Nick at Pelican Parts  
ken Comments: Thanks nick I really need all the help I can get. love my slk320 I am disabled and can only work on car 5to10 min at a time can't afford to take it to Mech. Thanks again love this site great help. Keeping me in my ride when everyone says get rid of it and get something else easyer to work on.
June 2, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
ken Comments: Tension pully on slk 320 what type of scokett fits this thanks
June 1, 2014
  Followup from the Pelican Staff: That is a tamper proof Torx but. likely T45 or T50. - Nick at Pelican Parts  
ken Comments: Trying to change alternater in my slk320 2003 ether center pice is missing or i need a hollow male star scokett to loseing tension on pully trying to change alternator
May 31, 2014
  Followup from the Pelican Staff: You likely need an inverted Torx socket. Can you share a photo of the fastener? - Nick at Pelican Parts  
71LS5 Comments: How different is it to change the tensioner and belt on a 1997 E320?
November 3, 2013
  Followup from the Pelican Staff: It is approximatly the same procedure. Some cars have automatic tensions so you have to adjust the tension yourself. - Kerry at Pelican Parts  

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