98-320, Vibration noise HELP - PeachParts Mercedes-Benz Forum

#1 08-10-2002, 09:43 PM

My wifes,98 ML320 has developed a vibration, buzz, rattle, what ever you want to call it. It occurs at 20 MPH and at 40 MPH. Rough roads to not make it buzz. Turning, accelerating, stopping has no effect. It will not do it standing still and will not do it running with all 4 wheels in the air. It sounds just like the left front brake dust cover vibrating, or a heat sheld on the exhaust. It is a metallic vibration sound. I have been over all the shields and body panels looking for this and if I had hair I would have pulled it out by now. Any suggestions, thoughts, directions to look. I am desperate enough to start paying the dealer to look for this and that I can not afford.

Is there something in the drive line that could do this? The shafts all seem tight, no clunks or any other strange noises.

Thanks in advance.

Gilly · #2 08-11-2002, 12:52 AM

We've had some bad/loose catalytic converters (internal matrix comes loose and vibrates internally). Try thumping on the cats with a rubber mallet, you'll definitely hear it if it's loose inside.

Gilly

#3 08-11-2002, 03:29 PM

That is exactly what it sounds like. I have thumped on them with my fist, just how hard do ? need to thump them? (I know that is like asking how many bees in a behive.) But should I not be able to get them to vibrate at a certain engine speed sitting still?

I am headed out to my shop to get a deadblow mallet and try this again right now. IF this is the case, isnt a defective cat a warrenty item till 100k?

Thanks

Gilly · #4 08-11-2002, 05:57 PM

Mark:
I'll try to describe how hard to hit; I'd say about as hard as you can slam it into the palm of your hand. That make sense? Not like your trying to dent it, but not a tiny little tap either, somewhere in between. You'll hear the difference if one of them has come loose.
I believe the cats are covered under what I think is called the "Extended emission controls warranty", check out your warranty info, it should be in with the owners manual packet. I want to say it's 80,000 miles, can't remember the time cut-off on that warranty. The warranty info should list what's covered.

Gilly

#5 08-11-2002, 09:22 PM

Many thanks for the good description. I hit them somewhat harder than you described, but they (all 4) sound as solid as rocks, even the muffler and related pipes. I can simulate the noise by striking the upper control arm on the left wheel. But this niose IS the rotor gravel shield. I have insulated it from the lower ball joint with a rubber pad which stops the vibration but has at this time had little effect on the noise at 20, 40, and 60 MPH. I will check again, the shield is tight and has no gravel trapped.
if the noise is not gone i am now to the point of taking the truck apart a piece at a time to find this, so any suggestions will be GREATELY appreciated.

Mark

Gilly · #6 08-11-2002, 09:57 PM

Mark:
Another idea is that the truck still might have the original front swaybar brackets,you can try moving the front sway bar up and down and see if there is any loosness. The usual complaint is a rattle when hitting sharp bumps, it definitely is heard in the front of the vehicle. The sway bar brackets were redesigned to make them quiet. You'll see the bracket on the top, goes between 2 "ears" that the upper bolt goes through. If the bracket fits solidly between the 2 ears (no gap) then it's the older style. If there is about 1/8 inch gap between the ears and the upper part of the bracket, then they've been replaced already. On the new style, only the inner steel tube that the bolts go through contact the mounting ears, the outer part of the bracket is narrower.

Other than that, i guess I'd have to do what you're doing, just find it.

Gilly

#7 08-13-2002, 09:55 PM

Thanks, again.
Our M does have the original bar mounts that fill the "ears" and yes it does clunk on some bumps. Never thought about the bar being a potential source of the buzz, but that is easy enough to test without and see if it helps.

Many thanks

Gilly · #8 08-13-2002, 09:58 PM

Other than that, Mark, I guess I would need to inspect it, nothing else I can think of at the moment, EXCEPT if you look at the back of the transmission, there is a pair of brackets that connect to the exhaust pipe, i did see one of these crack once and was making a noise, can't remember what type of noise it was, seems to me that taking turns would affect the noise or produce the noise or something.

Gilly