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Pelican Technical Article:

Drive Belt Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$25

Talent:

**

Tools:

8mm Allen, Mercedes Tool No. 104 589 00 01 00, 15mm socket

Applicable Models:

Mercedes-Benz 300CE (1990-93)
Mercedes-Benz 300E (1990-93)
Mercedes-Benz 300TE (1989-92)
Mercedes-Benz E320 (1994-95)

Parts Required:

New belt

Hot Tip:

Work on a cool car

Performance Gain:

Proper running accessories

Complementary Modification:

New tensioner

You should check your drive belt every six months 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 drive belt on the W124 is a very doable DIY; what it is not is as simple as doing it on and old Chevy. To replace the belt the radiator shroud and the fan will need to be removed. While you can loosen the belt to work on the accessories with the fan still attached, you will need to remove the fan if you are replacing the belt. A word of caution here before you begin. Depending on the engine and accessories on your car, there can be very, very little room to work between the fan and the radiator. You will need a short 8mm Allen to remove the viscous clutch on the fan. We ended up grinding an 8mm L-shaped Allen to fit in the space. You will also need Mercedes-Benz tool number 104 589 00 01 00 to stop the pulley the clutch is mounted to from spinning so you can remove the clutch. You can make your own tool by bending a piece of metal 6mm in diameter to fit in the locating slot in the bracket behind the pulley. Even with the Mercedes tool it can be a difficult and time consuming job. Be prepared to have and use a lot of patience.

The radiator is very expensive and delicate, and can be easily damaged while working around it. If you are going to be doing other work on the car and/or are worried about damaging your radiator, I recommend you remove it first. It is not a difficult job and can potentially save you a lot of money if you end up damaging it. Please see our article on radiator removal for further assistance. That being said, you certainly can remove the fan with the radiator in, but I recommend you put a piece of cardboard over it to protect it while working.

The radiator shroud is made up of two parts; the fan guard (yellow arrow) and the shroud (red arrow).
Figure 1

The radiator shroud is made up of two parts; the fan guard (yellow arrow) and the shroud (red arrow). The green arrow indicates where someone had installed the wrong hose. A hose pinched like this will severely restrict coolant flow and lead to all kinds of problems. Our project car ended up having a blown head gasket. This was probably one of the reasons.

Squeeze in the tab that holds the radiator overflow hose and slide it back out of the clip on the shroud and fan guard (red arrow).
Figure 2

Squeeze in the tab that holds the radiator overflow hose and slide it back out of the clip on the shroud and fan guard (red arrow). Set the hose and clip aside.

Slide the fan guard to the right (yellow arrow, when facing the guard).
Figure 3

Slide the fan guard to the right (yellow arrow, when facing the guard). Rotating the guard will free it from its retainers. When reinstalling make sure you install the guard with the "top" marking facing up (red arrow).

With the guard free from the shroud, place the guard back over the fan (red arrow).
Figure 4

With the guard free from the shroud, place the guard back over the fan (red arrow).

Remove the clip (red arrow) that holds the shroud to the radiator on the top right hand side.
Figure 5

Remove the clip (red arrow) that holds the shroud to the radiator on the top right hand side.

Remove the clip that holds the shroud to the radiator on the left side.
Figure 6

Remove the clip that holds the shroud to the radiator on the left side. The clip is located between the two hoses (red arrow).

Using care, slide the shroud out between the fan and the radiator (red arrow).
Figure 7

Using care, slide the shroud out between the fan and the radiator (red arrow).

Slide the guard off the fan and remove it between the fan and radiator (red arrow).
Figure 8

Slide the guard off the fan and remove it between the fan and radiator (red arrow).

This photo illustrates how the plastic pegs on the guard (yellow arrows) sit in the corresponding receptacles (red arrows).
Figure 9

This photo illustrates how the plastic pegs on the guard (yellow arrows) sit in the corresponding receptacles (red arrows).

At this point you can release the tension on the belt and slip it off of the alternator pulley.
Figure 10

At this point you can release the tension on the belt and slip it off of the alternator pulley. Place a 15mm socket over the bolt on the tensioner (red arrow) and turn the socket clockwise. This will un-tension the belt. If you are replacing the belt you will need to follow the steps below.

To remove the fan and clutch you will need Mercedes-Benz tool # 104 589 00 01 00 or you can make one out of 6mm rod.
Figure 11

To remove the fan and clutch you will need Mercedes-Benz tool # 104 589 00 01 00 or you can make one out of 6mm rod. The lower part of the tool will sit in a retaining groove, while the end of the tool sits in a hole in the pulley to hold everything while tightening or loosening the bolt (red arrow).

This picture shows what you will be doing with the tool.
Figure 12

This picture shows what you will be doing with the tool. The fan, clutch and pulley have all been removed for illustration purpose; you will be doing this by feel.

Insert the end of the tool (yellow arrow) into the retaining groove behind the pulley.
Figure 13

Insert the end of the tool (yellow arrow) into the retaining groove behind the pulley. You will need to rotate the pulley until the tool finds it seat in the pulley (red arrow); this can take a fair amount of trial and error. It is much easier to spin the pulley if you remove the drive belt. Please see step 10.

Here is an 8mm Allen that we cut off to fit the space between the nut and radiator.
Figure 14

Here is an 8mm Allen that we cut off to fit the space between the nut and radiator.

I recommend placing a piece of cardboard (red arrow) over the radiator then installing the 8mm Allen; this will help prevent damage to the radiator while you are working.
Figure 15

I recommend placing a piece of cardboard (red arrow) over the radiator then installing the 8mm Allen; this will help prevent damage to the radiator while you are working.

The bolt that holds the clutch and fan on is quite long so be prepared to turn it for a while (red arrow).
Figure 16

The bolt that holds the clutch and fan on is quite long so be prepared to turn it for a while (red arrow).

Wiggle the fan and clutch off the front of the pulley and remove it from the vehicle (red arrow).
Figure 17

Wiggle the fan and clutch off the front of the pulley and remove it from the vehicle (red arrow).

You can slip the belt off the front of the engine.
Figure 18

You can slip the belt off the front of the engine. This diagram illustrates the route the belt takes around the crank and accessories. Installation is the reverse of removal.

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Comments and Suggestions:
Bles Comments: Good evening everyone I have a 89 300e and I can't get my belt to stay tight,any suggestions
December 3, 2016
Ony632000 Comments: Dear Nick,
Thank you very much for your quick response. How ever I do have more questions. In your response you said:

"Followup from the Pelican Staff: Place a 15mm socket over the bolt on the tensioner red arrow and turn the socket clockwise. This will un-tension the belt..."

But please note that mine is not a 15mm socket but Allen Wrench. And I have done what you suggested with no effect. I know you are busy but I will appreciate it if you will look at the attached picture and tell me what I did wrong. Thanks a million.
July 16, 2016
  Followup from the Pelican Staff: You should check the tensioner for a HEX boss to place a tool on, If not use the Allen head to rotate it.- Nick at Pelican Parts  
Ony632000 Comments: First thank you for doing this DIY with pictures and words. I had no idea I could do anything in a car until I came to the US 16 years ago. I owe it all to people like you who take their time to do DIY. Thank you again.

However I have a question. Next to the picture #10, you Next to picture #10, you wrote,

"At this point you can release the tension on the belt and slip it off of the alternator pulley. Place a 15mm socket over the bolt on the tensioner red arrow and turn the socket clockwise. This will un-tension the belt. If you are replacing the belt you will need to follow the steps below"

Please kindly describe in a most idiot proof way how exactly you should release tension n the drive belt so that you can take out the serpentine belt; and how to re-tension it after installing the belt.

I have a 1991 Mercedes 300 E. It is a 124 chassis. I am replacing the smug air injector on it. I took it apart a long time ago because I thought the problem was the water pump. When I discovered it was the smug pump, it took me a while to afford a new one. No I have forgotten how everything was. Thanks you again for your help.
July 15, 2016
  Followup from the Pelican Staff: Place a 15mm socket over the bolt on the tensioner (red arrow) and turn the socket clockwise. This will un-tension the belt.

Do the same to hold the tensioner in the released position when reinstalling the belt. - Nick at Pelican Parts
 
LCHutton Comments: Besides providing the belt length info, I wondered if there is a different Tech Article for my engine? The Tensioner set up and Power Steering Pump attachment seem to be different than described in this Tech Article. My engine has a sticker on it with the following: 104.992. That's a 3.2 litre engine in a 300E
November 25, 2015
  Followup from the Pelican Staff: If you take the belt part number, you can usually figure out the length using the belt manufacturer's website.

Your engine will be different, this article is for four-cylinder models.

This article may closer to your model:

http://www.pelicanparts.com/techarticles/Mercedes-W203/ENGINE-Replacing_Your_Belt_Tensioner/ENGINE-Replacing_Your_Belt_Tensioner.htm - Nick at Pelican Parts
 
LCHutton Comments: You are certainly correct about working on the W124 104.992 engine as compared to my 1962 Chevy Impala. You probably could have changed a belt in that car in 15 minutes.
I'm doing the belt replacement along with replacing the water pump due to an O ring leak between the Pump and Block. After removing the Power Steering Pulley, I was able to remove the Drive Belt without removing the fan. Will I have to remove the fan later to get the new Belt on?
I'm having conflicts with your directions for the Water Pump compared with my engine. I had to remove 3 bolts to loosen the Power Steering Pump and it still won't come out. My tensioner pulley has a cover, not a 15mm hex head and there is a hollow adjusting Bolt near an arrow pointing at a ramp as in your 190E directions. Should I be using different directions?
I have found many other conflicts with with this 1993 300E with a 3.2 L engine. For example, Pelican Parts says the Drive Belt is 2415mm. My MB Manual says 2445mm. Pelican Parts is correct.
November 24, 2015
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 
Ray Comments: I'm about to remove the fan clutch from my 1995 E320 is the center bolt left-hand or right-hand threaded? i have been trying to pull it out turning in a clockwise direction, I'm i correct?
October 15, 2015
  Followup from the Pelican Staff: Rotate to the left (when facing engine) to remove. - Nick at Pelican Parts  
Steh-fan Comments: What is the correct torque for the bolt that holds the clutch and fan??
September 15, 2015
  Followup from the Pelican Staff: I don’t have that info.

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
 
85 DSEL Comments: Isn't it possible to remove the fan/clutch bolt before removing the belt? Hold/wedge the fan while turning the bolt out?
May 5, 2015
  Followup from the Pelican Staff: Usually the belt will slip, not tight enough of a grip to hold it still. - Nick at Pelican Parts  

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