Does that title make any sense?

If it does than I'm wondering if any of you have had experiences with the bearings going out in the belt pulleys. I know that the bearings will all go bad with due time, especially the smog pump, water pump, etc., but I think on my car the idler pulley is going bad. There's a noise somewhere in the area of the idler pulley but I can't pinpoint it to that pulley since it could be the other pulleys around it. Looking at the image below it's the number 5 pulley. I always thought that these pulleys and bearing never have problems so it's a surprise to me.

Guess I might have the take the belt off and inspect them one by one.

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500

On my M104 engine, the idler pulley bearing and the air pump pulley bearing went bad, somewhere between 135,000 and 150,000 miles.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Try a stethoscope, carefully, you should be able to tell exactly where the noise is coming from. Also take off the belt and see if the noise goes away entirely.

I'll just take the belt off and see if I can feel any resistance with my fingers as I turn the pulley. Hope it will work.

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500

My experience with pulley bearings is that when they go out they make a helleva lota noise.

When my air pump bearing went bad, it made a sound like a screaming chicken.

It was so bad that when I was driving through a supermarket parking lot, people walking by had to cover their ears.

Needless to say, I was very embarrassed.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

I agree, my air pump also went out. At first the sound was hardly noticeable, but after time it got louder and louder until it finally seized up. I just don't want this to seize up so I might have to take a look at it very soon.

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500

When my bearing (M103) started growling, I recall forcing grease into the bearing's tiny seam (accessible by removing a plastic cap). Used finger to squeeze grease into the seam, then a toothpick to push it further towards the race. Not much lube got applied, but it's been quiet for 2 years now.

I heard a distinctive "Click" "Click" "Click" (and it wasn't Santa and his tiny reindeer) on my M104 one year, and even my stethoscope pinpointed the air pump pulley as being at fault.

My indie checked it out and replaced the belt. Turned out the old belt had a chunk missing on the toothed side, and it made itself known when it rounded that pulley!

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

My car is very low mileage, but it started to make a lot of noise around the pulleys. I thought the worse and thought the water pump was going out.

The tech check it out and it was the tensioner pulley. A small roll that tensions the belt. Incredible easy and chip to fix.

He told me that this is a regular problem with M119s.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]