Shredded Serpentine Belt, 95 E320
 

Within less than a year and 10k miles after an OEM german serpentine drive belt was put on the car (by a mercedes master mechanic), it snapped or shredded. The person driving the car at the time did not realize the belt had let go and continued driving for about 10-12 more miles, suspected a failed alternator (as the light was on). When I diagnosed the shredded belt, the car was transported home by flatbed. The belt was in a hundred strings, all wound in and behind many of the pulleys. I removed as many as I could see, all the pulleys spin freely (except crank, of course) Because the car was driven with no water pump running for those 10 miles or so, there was no coolant in the overflow tank, so it must have been hot. The saving grace for the engine was 1., temps in the single digits; 2., secondary water pump circulating coolant a little plus twin electric fans operating at full thrust; 3., the m104 is a tough engine.

After recharging battery, adding coolant, and a new belt (this time a goodyear gatorback), the engine started and seemed to run fine. There is more belt stuck behind the fan viscous drive, so the fan runs fully engaged all the time, resulting in engine roar and slow warming up. Other than that, the car seems fine.

The question is, why did it break and shred?

The first thing I noticed about 2 weeks before the problem was little puddles of oil forming under the car. Keep in mind the head gasket had been done at the same time we got the new serpentine and that had cured oil leakage. The oil leaking had gotten all over the pulleys and the drive belt was wet, something that had not happened during the headgasket oil leak. Although oily and wet, the belt seemed fine and all accessories seemed to be working fine. I diagnosed the leak as from the rear suspension fluid, either the hoses going from the tank of fluid to the pump or from the pump itself. The fluid level in the reservoir went to a low level and stopped leaking.

Upon inspecting the vehicle the day before the belt shredded, I cleaned up the wet hoses from and to the power steering / rear suspension pump, tightened a clamp, and added more suspension fluid (not to the correct level in case it just leaked out again, but quite a bit.) I ran the engine, and the fluid did not seem to be leaking.

I then noticed something flailing on the engine side of the serpentine drive belt. Shutting off the engine, I noticed very light and intermittent shredding on the engine side of the belt. The shredding was about 1mm of belt was peeling, and I broke it off. I noticed one of the power steering lines seemed very close to the belt and this seemed to be the cause of the light shred. I securely relocated the hose, and since the belt had just the slightest damage I deemed it fine to run. Of course, the belt shredded the next day!

Could the hydraulic suspension fluid on the belt and pulleys have caused the belt to slip off and break / shred?

Before replacing the belt, I felt all of the pulleys and they all seemed smooth with a couple having the very slightest of imperfections. After three days of very cautious driving, it seems fine.

Any thoughts on why this might have happened would be appreciated. Also, how do I remove the fan / pulley, so I can get the rest of the belt fragments out?

Finally, the air pump: the wiring going into the clutch was hit by the flailing belt and is now bare. There are only two wires going in, a red and black. About 1" of wiring is exposed. I taped off as best I could, but the insulation is gone even as it goes behind the metal pulley. Nothing seems to be shorting but not so sure the pump is working anymore either. Any way to remove the pulley / clutch and get at the wiring easily?

Thanks in advance.:confused:

First - check the alignment of all of the accessories on the engine - they should be very close to exactly in line. This will cause the type of fraying you saw on the belt. Possibly something wasn't re-installed right during the headgasket job.

Second - belts don't like oil - that may have been the cause of the failure.

Third - if I'm right, the air pump will only run briefly (like 100sec) after a cold startup - injects more air into the exhaust to help "light off" the catalytic converter.

Fourth - don't know about access to the wires, sorry.

Shredded belt
 

Hydraulic oil will damage the belt. As far as the exposed wires on the air pump clutch , You should either replace the clutch coil or disconnect it from the connector further up the wire.
Regarding the air pump;Did you listen very carefully for bearing noise when spinning the pump pulley? Air pump pulleys lock up frequently due to bad bearings. If they are noisy order pump pulley repair kit #104 140 02 86 it comes with pulley, clutch,and coil with wire attached. List price $470.00 but I'm sure you can shop the net. If you can't find one anywhere PM me.
Good luck Mike

My Theory:

1.) The belt probably had a small crack or tear that you never noticed,
or which you felt was negligible.

2.) The person driving the car ran the engine at high RPM for an
extended period -- say 60 seconds.

3.) The belt disintegrated.


Premise of Theory:

This is what happened to me in my 260E. The belt had a small
tear -- like somone took a toenail clipper and snipped a small piece from
the edge. One fine evening, for reasons unknown, I felt compelled to shift
into second gear while driving down a small hill. The engine revved to about
5000 rpm and, seconds later, the belt flew apart, causing all dash lights to
come on.

I was less than a mile from home, so after pulling over, shutting down, and
then restarting (to make sure I could) I drove home. The coolant
temperature began to rise rapidly and by the time I got home it was in the
red. When I opened the hood I saw the shredded remnants of the belt, and
the coolant in the reservoir was boiling.

You should probably have another chat with the person who was driving, to
find out what really happened. How hard were they driving the
car/revving the engine? Did they not think something was seriously wrong
when the entire dashboard lit up after the belt was gone? Etc.

Thanks for the replies so far--

The person driving was making an 85mph pass up a two-lane hill. RPM's were probably around 5000+, which is no problem for this engine, but as mentioned there was a negligible belt tear. Yes, this person (no names mentioned!) has learned a lesson.

So far, so good. Continuing to monitor new belt.

Car was obviously in a low gear at the time, undoubtedly after downshifting when you -- er, I mean the nameless driver -- floored it to make the pass, guaranteeing belt failure.

Consider yourself lucky that this did not happen in the heat of summer.

Yeah, lucky for the cold weather. Fairly abruptly we may put the wagon for sale next week should we purchase a 2000 ML320 this weekend. The wagon has been great, and personally I think the 24V m104 is better than the 18V V6 in the ML. However, this ML is 1-owner and particularly well cared for. (Mobil 1 every 3k miles)

Any ideas of how to get the main engine fan off to remove belt fragments still stuck in the viscous drive?

Thanks