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Drive Belt Tensioner Replacement
 
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Pelican Technical Article:

Drive Belt Tensioner Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$30 - $80 drive belt

Talent:

**

Tools:

13mm, 15mm socket, 6mm Allen

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 tensioner and drive belt

Hot Tip:

Don't work on a hot engine

Performance Gain:

Will not leave you stranded at the side of the road

Complementary Modification:

Check coolant hoses and clamps

The drive 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 pulley 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, pulley and drive 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 replace 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.

NOTE: This article was written for the earlier style tensioner, not the late W124. There is not a 15mm bolt on the tensioner of them rather a 5 or 6mm IIRC. There is also no instruction how one is to safely go about releasing tension on the belt via the belt tensioner adjusting rod. Before any attempt to loosen the belt, be sure to loosen the large center bolt 10mm Allen on the late style of tensioner. This will allow the tensioner to 'hinge' or 'swivel' on that axis. Another thing not explained is the fact the power steering pulley MUST be removed in order to get the old tensioner out of its nest. There is a three armed bracket that kinda holds the tensioner in place and one of the arms reaches over on to the steering pump and its bolt head is buried under the pulley. One more thing here is that the bolt going through the steering pump as a nut 13mm on the back side of it that likely needs to be held.

You will need to remove the shroud and fan to replace the tensioner. Please see our articles on fan and shroud removal for additional assistance.

You will need to remove the belt from the pulleys.
Figure 1

You will need to remove the belt from the pulleys. Before you take the tension off the belt loosen but do not remove the three 13mm bolts holding the pulley to the water pump (yellow arrows). Then place a 15mm socket on the bolt on the tensioner (red arrow), rotate it clockwise and slip the belt off of the pulleys. Note: if you are only replacing the tensioner pulley you do not need to loosen or remove the water pump pulley. Please skip to picture 4. Hoses have been removed for photographic purposes only.

With the belt off remove the three 13mm bolts form the water pump pulley (red arrow, one shown).
Figure 2

With the belt off remove the three 13mm bolts form the water pump pulley (red arrow, one shown).

Wiggle the pulley off the water pump (red arrow).
Figure 3

Wiggle the pulley off the water pump (red arrow).

Place a 15mm socket over the pulley nut and remove the nut and pulley (red arrow).
Figure 4

Place a 15mm socket over the pulley nut and remove the nut and pulley (red arrow).

Use a 6mm Allen and remove the three bolts holding the tensioner to the engine (red arrows, one hidden).
Figure 5

Use a 6mm Allen and remove the three bolts holding the tensioner to the engine (red arrows, one hidden).

If you are only replacing the pulley make sure there is no damage to the tensioner in the area where the pulley sits (red arrow).
Figure 6

If you are only replacing the pulley make sure there is no damage to the tensioner in the area where the pulley sits (red arrow). Damage in this area that will cause an uneven area for the pulley to mate against will lead to failure of the new pulley.

Installation is the reverse of removal.
Figure 7

Installation is the reverse of removal. Here is a diagram to make sure you route the belt correctly.



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Comments and Suggestions:
statiowagon Tom Comments: 1995 E320 wagon
I find your web site very, very helpful.
I have a bad front bearing on my secondary injection air pump located just above my alternator.
Do you have any directions for removal and service?
May 3, 2016
  Followup from the Pelican Staff: All W124 articles are here:

http://www.pelicanparts.com/techarticles/MBZ_Tech_Index-W124.htm


If you don't find 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
 
TulsaE320 Comments: In response to 85 DSEL's comment, this article details the LATE internally dampened tensioner, not the earlier externally dampened version, at least according to everything I've read to this point. My wagon is a late-production '95 model, and uses the same tensioner and 1470 pulley detailed in the photos here.

85 DSEL is correct, however, in his assertion that the power steering pulley be removed for full access to the bracket. Embarking on this project tomorrow!
December 29, 2015
  Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
 
Lofty Comments: Regarding the tool required to hold the fan unit from the back, I used a 6 mm threaded rod, be careful with the bending of the piece that goes into the hole, sharpen the end of that bit to 2mm point, took me one go to find the hole, and I am an old aussie soldier !
December 29, 2015
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.

- Nick at Pelican Parts
 
85 DSEL Comments: It may be worth noting that this article was written for the earlier style tensioner, not the late W124. There is not a 15mm bolt on the tensioner of them rather a 5 or 6mm IIRC. There is also no instruction how one is to safely go about releasing tension on the belt via the belt tensioner adjusting rod. Before any attempt to loosen the belt, be sure to loosen the large center bolt 10mm Allen on the late style of tensioner. This will allow the tensioner to 'hinge' or 'swivel' on that axis.

Another thing not explained is the fact the power steering pulley MUST be removed in order to get the old tensioner out of its nest. There is a three armed bracket that kinda holds the tensioner in place and one of the arms reaches over on to the steering pump and its bolt head is buried under the pulley. One more thing here is that the bolt going through the steering pump as a nut 13mm on the back side of it that likely needs to be held.
May 6, 2015
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 

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