moretech

I've picked up some kind of metal like rattle a couple of weeks back, way far back near rear wheel area.
Has been there awhile now, comes and goes, definitely metal on metal sound. Car runs fine no messages. I have not changed any tires around. ABC works ok, no leaks, no messages. Can disappear for awhile then return. It is there at idle--sometimes, varies with engine rpm, gets less or not at all at high rpm. The noise is also present with car in slow motion if you listen carefully but still sometimes not at all, can't hear it at speed.

moretech

cyglee

Could this be the dreaded gas tank loose baffle rattle? Do a search and please let us know.

moretech

I tried the full tank of gas (repair?) idea. No change in sound tank full up--so that was that unless the tank trick fails at times. Can a rear accumulator get rattly? But still ride quality is unchanged and no warnings. I'm trying to get fluid up to temp for a good lower mark reading but I think it will be fine. If I don't get this figured quick I can get my indy to give me an opinion. I have an indy who doesn't work on MB but he is glad to give a look at this kind of thing on his rack, been with him 25 years. I have another indy who does do MB if I can't get it fixed myself. In the old days I'd say it's a broken tailpipe hanger clamp.

Ghostty

Could it be the cat converter? I had that on my slk, rattling noise from underneath the car. Pretty easy to spot by a good mechanic. It should be a free inspection any way. And it can be only one, not both.

moretech

Right on, may be a cat, but when I look underneath it seems sound is too far back to be that. Cats seem more forward. Did you get BB's out the tailpipe when it went bad? No BB's here.

moretech

Ghostty

What do you mean by BB?
the sound might spread trough the exhaust, without the car lifted (or getting underneath it) it's hard to say by just listening to it.
it also was only when idling or low rpms, never heard it when driving

moretech

I had a Buick and when the CAT went out and all sorts of literally BB's of the catalyst ( I mean BB sized beads) came flying out the tailpipe for days. Every time I started the car out they came bouncing down the driveway! I do not know if MB has particle matter such as that in the catalyst design. They told me a large baffle that kept the BB's (catalyst beads)in place broke and the catalyst then could escape out the tailpipe.
moretech

Ghostty

Nope, was nothing coming out of the pipe, just the rattling noise. Maybe because the cat is before the manifold, so if something does get out it might get stuck there?

moretech

update:
Ok fellows I got way under her and banged on a converter ( I guess that was it). A round can about a foot long midway down the car's length, driver's side. Sound disappeared. Came back in awhile, hit it again, gone again. Did this several times, same effect. Read in the forum some do not have oxygen sensors and car can run without it ok. How much you think one of these are? Anyway does indeed appear to be a faulty baffle in the cat. (resonator?) moretech

Ghostty

I paid $350 for the cat only+labor. Some shops will do cat only, some won't. Here, in CA, we have to pass smog check. SO the oxigen sensor is to be left there for smog check (yes, I know &#128518. If your state doesn't require smog, you could remove it too. But, imho, the sensor is there for a reason.

Back to cat - some shops will replace full exhaust only - and that's expensive (for the slk the exhaust only was $1200+). If lucky enough and find a shop who will do cat only - should be around $500. They cut it out and weld the new back in. 1-2 hr job at the max. Dealer prices - you know yourself

Regards

P.S.

​​​The oxigen sensor is there to check if the emision is lean/rich, and adjusts the air/gas mix accordingly. Not sure if it will trigger check engine light, but, on the long run, issues may arise due to no info for the engine on how rich or poor is the gas mix for the vehicle. Too lean is less dangerous than too rich, but both can create built-ups that eventually will damage the engine.

moretech

Ghostty,,
thanks for this info but to tell the truth I really see no wires of any kind from either of those
cans. maybe they are monitored somewhere else down the line. My indy will do just the cat or whatever, I already worked on that part. Will let you know how it turns out. thanks a bunch
moretech

Rudeney

The catalytic converters are right below where the exhaust pipes attach to the manifold. There will be O2 sensors before and after each of these. They sit right along the sides of the transmission bell housing After that, there will be resonators that are just behind the transmission and just before the X-pipe. Behind the rear bumper are the mufflers. I suspect you have isolated the noise to the resonators. They have no effect on emissions, just sound. Many people remove them to get a different exhaust note.

The problem could be a broken resonator, but it could also be that the catalyst in the converters are coming apart and particulate from them is lodging in the resonators.

Ghostty

Well, when I did it on my slk320, it actually was a bad cat converter. After replacing it - everything came back to normal. You do have a point too, that's why I said to take it to a exhaust shop, they deal with this every day, they can say for sure is it a bad cat or a resonator with stuff inside. I love the forum for ideas and pinpointing, but on my end I still double check with mechanics that deal with the specific issue on daily basis))

Regards


P.S.

Agree, if the sound is coming from the resonator, there is no sensors to it. The sensors are for the catalytic converter. Now you make me wonder if there's a way to find out if it''s a bad cat without cutting it down.... Also haven't heard of resonators going bad.... So, if it's a bad cat, needs to be replaced. But, now because the stuff got into the resonator, will you need to replace that too, or it can be cleaned/removed?

Rudeney

MBZ's official repair for a bad cat is to replace the entire exhaust system. That is because the molten material that breaks away from inside the cat ends up in the resonator(s) and muffler.

Ghostty

Oh, boy! Don't want to find out what would the bill look like at a dealership for a job like that 😅

Rudeney

To give you an idea, here are parts prices:

http://www.mboemparts.com/auto-parts...omponents-scat

List on a new front section (cat, pipe, and resonator) is $706. The muffler and its pipe is $416. Throw in a few gaskets and shop supplies and you're looking at $1200 per side. Labor at book rates is 3 hours, so under $3K. But, if you buy all those parts at the discounted price and DIY, it's around $1,800. And you could try not doing the mufflers and see how it goes, so for the cats and resonators, it's under $1200. if the mufflers end needing replacement, then just buy them later.

moretech

My indy took both out and straight piped it on both sides. Hardly noticeable change in sound. All is running fine. Baffle had failed. $120 total charge.

moretech

starfan

. . . if like a professional repair of the tankproblem (r230 baffle-broken-tank), look
here: http://www.mercedes-tankrepair.com/

The amateur repairs create more difficulties than improvement (tanksensor does not function later).

This guys from Stuttgart come to your place (repair the tank inside the car) - also you can send them the rebuild tank by UPS from your workshop

Blazeracer

Awesome forum. Had a knock develop under my SL last week. Took it to muffler shop, 180 for a new left rear cat installed.