W124 - What would cause the belt to keep shredding??
 

Car in question is a 1986 300D Euro (no turbo).

I am now on my second new belt, after having a reputable shop replace the tensioner, the belt shock, the fan pulley, and of course the belt itself. The first belt was done as an emergency repair by another shop on a long road trip coming back from Maine.

It appears as though it is shredding on the inside, towards the motor... again. But I'm not entirely sure. The texture on the outside appears to be "smoothing out" - is this just the way these belts wear in? The ribs appears to be fine I don't see any fraying. But I'm worried I might be on borrowed time.

Opinions?

Is the belt riding on the tensioner pulley evenly? Does it show signs of self-destruction before it goes or does it just all of a sudden fail?

The only thing I can think of is that the 'reputable shop' made an error in the installation of the tensioner, left out a spacer or something. As an experiment, however, you might try replacing the belt with a new one. Get a completely different brand and see what happens. If the new belt also fails, then go back to the shop, ask them to check their work. If they're really concerned about their customers they won't even charge you for the double-check. Make sure you keep and bring with you the worn belt(s). If that fails, try a different shop.

As personal experience, I can tell you that part of the tensioner assembly, replaced by my 'reputable mechanic,' failed after a year or so on my '85. The mechanic went through the system, found that the tensioner had failed (bad part from the manufacturer). Did the repair the second time for free.

Jeremy

Have you put your hand on all the surfaces which the belt runs across in it's daily travels?
It does not take much of a rough spot as often as a belt passes across it to ' do it in' in short order...

the correct spacer behind the tensioner is very important.

how is belt riding over the tensioner pulley? it must be 100% on the pulley.

617 guy here trying to learn about the later diesels...just wondering, is this a serpentine belt? How many ribs?

Is one of your belt accessories frozen?

Yes they have a serpentine belt.....just like the M103's/gassers.....I think its a 5 ribbed belt....but I may be wrong.

Personally I still think the V-belt system is more durable....more of a pain to install/remove (though not really in my opinion).....

It shows signs of self-destruction before failing. I THINK this one is now in the beginning stages, and I can probably drive a couple hundred more miles before it ultimately fails (but I won't of course).

Be sure its a Metric belt,and not in fractions.

also pulley alignment
 

Check to make sure all your pulleys are in the same "plane" or alignment. If you have replaced an accessory such as an alternator or A/C compressor, the pulley may end up too far forward or back from the other pulleys. Hope you find the answer.

Chuck

I'd have a good hard look at the tensioner arm and pulley.

When ever I have run into this problem it has been after changing something with a pulley and then finding out that that one pulley is not in plane with the rest of the system. I would take it back to where you had it worked on and have them check to make sure everything is in line.

brand new belt lasted about a week due to spacer not being installed behind tensioner. i noticed a little bit of fray, then a few hunderd miles later it exploded, took out vac lines, ac elect wiring, upper rad hose, lower rad hose, and wound itself around the crank pulley so deep it took an hour to remove the bits. live, learn...should of stopped and figured it out when i noticed the fray starting, looked similar to pics above. didnt raise my concern but i guess it should of.

300D NA W124 6cyl donk

I had a quick look at my belt yesterday, my tensioner is running on an angle.

Are tensioners hard to fix on my ride?

Is there any where on the web or this forum with tips on how to and what to look 4?