Serpentine Belt

[Crosbo]

This weekend I noticed the serpentine belt on my '89 300E is beginning to look a little worn, with the ridges having several cracks. So while at the dealership I picked up one of the expensive pieces. Question is, after looking, what all do I have to take off to replace the belt? How in the he** do I get to it? Suggestions?

What are the two connections under the passenger footwell, behind the black cover? The black box has "Becker" on it. Is this part of the stereo system or the factory alarm? :confused

I had an after-market alarm installed and they told me the factory allarm had to be disconnected because it was interfering. Thanx

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'89 300E 3.0
'82 350SD

[jeffsr]

On the 300E, the fan blades and fan shroud will have to be removed. It can be done w/o doing these steps, but it's almost impossible to get to the tensioner bolt w/o at least moving the shroud out of the way. At any rate, next step is to slack off the big bolt in the center of the belt tensioner. Back off the the tensioner adjusting bolt (sticks up near the power steering pump resevoir) take off the old belt and reverse the process to reinstall. If you don't have a routing diagram, take notice of how the belt is routed around all of the pulleys. Good luck.

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Jeff L
1987 300e
1989 300e
1987 BMW 325

Is this procedure the same for the 1991 300d 2.5?

[Rob Pruijt]

It can also be done by removing the lower alternator bold and pull the alternator upward to remove the tension. Al least this worked for my 300SE.

Good point, I did not think of that.

Pay close attention to the belt tensioner pulley. I am told that they tend to wear out after 100,000 miles and will "fall apart after the belt tension is removed. You will then be stuck until you get more parts. If you are not sure hoe to change a serpentine belt, this may be a liitle too involved for you. If you look down on the belt and pulley, a worn tensioner pulley will be cocked over a little.

This info was provided by a tech at the local Mercedes dealer. I spoke to him after I picked up my car for the trap oxidizer recall. I have tha parts but have not installed yet. I would think another member could confirm the belt tensioner issue. Or wait till next week and I will confirm for you!

Regards,

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Deezel
87 300TDT
150,000 miles

[jeffsr]

I would not use this method to change the belt. You need to reset the pointer on the tensioner for the new belt. You will not get accurate tension w/o this step as the old belt will be stretched and just retightening the alternator will not be accurate. The tensioner is designed to properly load the belt. That's why they put it there..

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Jeff L
1987 300e
1989 300e
1987 BMW 325

I am going to work on this, on Sunday. After I remove the fan and shroud, I will be able to get a better picture of the scenario. I am hoping that it will justbe the belt tentioner shock and not the actual tentioner. If is the tentioner, I will just have ti bite the bullet and buy a new one. I'll keep you posted as to what I find.

[jeffsr]

The shock is just that, a shock absorber. It damps out standing waves and vibration in the belt system. It does not apply any useful tension to the pully. Look at where it is located. The picture should speak for itself.

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Jeff L
1987 300e
1989 300e
1987 BMW 325

[This message has been edited by jeffsr (edited 05-06-2000).]

[Crosbo]

Holy Behr Batman!!!

I was attempting to take off the fan bolts when the upper radiator outlet gave way. Just about right, only wanted to do a little preventive maintenance by changing the belt and end up buying a new $300 radiator. Could have gotten it cheaper but not until Wednesday and they don't take Visa! (I think my famous last words were, "I'm not gonna pay someone about $100 just to change out a belt, not when I can do it myself!)

Good News, got the new belt on!! But, the large bolt in the middle of the tensioner would not budge?? The tension pointer is at the notch on the far end of the triangle (closest to the camshaft) The tension adjustment bolt runs from one end of the spectrum to the other without a problem. Is this correct? What part of the scale should the tension be adjusted to? This is similar to the serpentine belt on my wife's suburban but the bolt doesn't seem to be acting the same.

Are all the procedures and settings on the CD available in PartShop?

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'89 300E 3.0
'82 350SD

I hope someone gives a reply, I was just thinking about this myself.

[jeffsr]

Congrats on getting the belt on...But, as you describe it, the tensioner is not properly set. The tensioner retainer bolt, (the big one in the middle) has to be loosened to adjust tension. If you don't loosen it, you are racking the rubber coupling inside of the tensioner against itself. Two things will happen. You won't get an accurate setup and you stand a good chance of tearing the rubber coupling loose from the inside of the tensioner housing. With the pointer at the far left, you are a max tension. You cannot set the pointer w/o loosening the tensioner retainer bolt. It can be loosened. It's a big one and has a fair amount of torque applied. When you get it loose, about 2-3 turns after it breaks free. Crank out the adjuster until it is loose. Set the pointer by pushing down on it gently and move it to the far right of the triangle. Then crank down the adjuster until the pointer is at the far left of the triangle. Retighten the retainer to the correct torque and you should have it right. Bummer on the radiator, but better in the driveway than on the highway. These are known for breaking the upper outlet. Make sure your new one has a metal reinforcement sleeve inside the neck.

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Jeff L
1987 300e
1989 300e
1987 BMW 325

[Crosbo]

Jeff I want to thank you for all your assistance. I was using a 3/4" ratchet on the bolt but it still didnot break free. Will try again tomorrow morn. I am attempting to put my black baby back together tomorrow. Gonna try to regain her favor by adding the new Bosch's and plugwires I picked up for her today, new filter and Valvoline, as well as adding WaterWetter then soothing her skins with a new bottle of Lexol, then a sponge bath and a rubdown(wife never should have left me alone in the parts store). Wish me luck, I hope to get lucky!!

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'89 300E 3.0
'82 350SD

I had a post on another website and wanted to share some of the replies. It is kind of funny that across the US, there are several people doing the exact same repair as me, right now.
Thank you to everyone for continuing to educate all of us!!!
Here are the replies:

Anyone that can inform me of how to change the belt, it would be greatly appreciated.
Thanks in advance.

Re: How to change sepentine belt on 1991 300D 2.5
Usually you crank the nut with your socket wrench to release the tension on the serpentine belt. This is as generic as I can get with your generic question.

Re: How to change sepentine belt on 1991 300D 2.5
Thanks!

Re: How to change sepentine belt on 1991 300D 2.5
Ari, If you release tension on the spring holding the tensioner up (put the lug wrench handle into the hole on the plastic piece that the tensioner spring clips over - unscrew the nut that goes through the plastic piece and the head - and applying tension pull the bolt clear - then lower the plastic piece with the lug wrench 'til the spring is "limp") then you can relieve tension on the belt and remove it - putting the new one on is the reverse - sort of a Chinese puzzle, but it CAN be done.

Re: How to change sepentine belt on 1991 300D 2.5

I am going to give this a try in abou 1/2 hour, so I get get to the bottom bolt on the shock tentioner.