Oh boy, I discovered on my new SDL that there was a big flaw in the exhaust pipe that had been covered up with some sort of wired on sheath. I was getting exhaust smell in the car and could see it emanating from the flex area under the hood. The next morning, I jacked it up and, oh yes, there it is. A rusted spot big enough to stick fingers in.

As bizarre luck would have it, I still have the entire exhaust pipe with mufflers from my '81 300SD, now sent to the great dismantler in the sky. I had removed it at one point and forget to send it on. The flex joint and surrounding pipe, perhaps even the flange going to the manifold looks identical to that on my 300SD. You can see superficial rust from the pics but it's way solid compared to the rusting original.

I had done an air leak test with the blow side of one of my cheapo Home Depot shop vacs, the $29.95 Stinger - I have 3, I saved the first two after they broke and when the 3rd broke discovered it was only a bad switch on all 3. Moral to that story, don't throw that stuff away, 1/10 of its life span is defined by the original switch.

One I use only for wet vac, no dust therein so I put it on one end, duct taped it to mostly seal and found major leakage under the sheath, which I, of course, expected. But leaking nowhere else.

I then did the same with the 300SD exhaust pipe. Putting soapy water on the flex part, I got copious bubbles. Wasn't surprised by that, would be real hard to make that air tight.

I might just weld it on for now, but I might be a fool not to get a new unit. Last night I found flex joints - I swear - in the Pelican Parts catalog, I should have saved the link because I can't find it now.

I found something similar on another site, must be a competitor because it won't allow the link to post. No sweat, I'd rather buy it from Pelican. Looked like this:



Probably shouldn't be stainless, harder to weld.

Question being, some leakage is likely acceptable at the flex joint, no? It is making bubbles but the stream of air making it past the wadded up paper and duct tape at the end, this on the other side of the mufflers, is way stronger than what I'm feeling blow out from the flex joint.

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1986 300SDL, 362K
1984 300D, 138K

I don't think that coiled flex section leaks because there are no soot trails. I have some pinholes in the aftmost muffler which I only see because of soot.

Sixto
83 300SD
98 E320 wagon

The flex joint in my SDL looks like the rusty one in the lower 2 photos. The braided sheath is just a different type of flex joint, basically the same thing as the lower style with a braided cover. Don't ask me what the braided cover is for, I am not an exhaust expert.

If the rest of the exhaust pipe is healthy, you might be able to get away with welding in a new flex joint if yours is leaking.

Another spot you may have leaks is the pre-muffler. It is a "square" shaped muffler roughly under the driver's side rear passenger seat. Mine has several cancer spots and a rusted seam. The temporary repair was to fill the holes with muffler paste and reinforce with some scrap steel. Eventually I'll have that portion straight-piped and do away with the pre-muffler.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Good point. It definitely blew soap bubbles but there wasn't much more avenue to go anywhere else. It will definitely be a huge improvement over what I had.

One small issue, the three nuts holding the forward most part to the manifold were on very tight. I had to cut the first one off after it rounded. I abused the stud somewhat, I may just clean it off with a die and reuse it. Not sure how hard it would be to get that out in that tight space. I assume it's pressed in.

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1986 300SDL, 362K
1984 300D, 138K

I think I'll be able to weld it in all right. I had hoped they might be identical back to the midway joint, but they're not. The SD has a greater vertical rise and the SDL is a bit longer before it reaches the point of the junction.

I cut off the SD part with several inches to spare and place it up on the manifold. The flared joining point is identical in size to that of the SDL. They are not exactly the same shape, the curved neck part I mean, but the SD unit fits just fine. I'm going to lightly bolt it in place and then put up the SDL rear part, mount it to the joining flange that is, and mark where to cut and weld. Luckily, I'm getting away with only welding one joint. I was afraid I'd have to weld on both sides of the flex section.

I'll check out the rest of the muffler, good tip.

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1986 300SDL, 362K
1984 300D, 138K

Well, THAT was not an easy job. Turns out thinking that I could use the front end of the part from the SD, the flared bell that attaches to the manifold and the upper joint of the flex fitting, was the naivete of youth. It was close, it would have cleared the body, though by less than optimal amounts. But at the bottom getting a decent joint with the rest of the exhaust system was just too difficult. Would have required a splicing in a small piece.

So I cut and welded a couple of inches on either side of the flex fitting. The flex part is stainless and the bonds to the steel were solid so I feel plenty comfortable using the old part as opposed to buying a new one. Not only a lot cheaper, didn't have to wait to get it plus I have the satisfaction of having a piece of my old 300SD serving a function, and not a small one, in my new rig.

I was dead in the water til this job was done. Any leakage from the 'new' joint is tiny, especially compared to the wide open channel exhaust fumes previously had, and being funneled strongly up and into the engine compartment. No wonder I was smelling fumes in the cabin.

I sprayed soapy water on everything and watched it immediately after starting up and all my joints are good, the flex line put out a few bubbles but that down at the bottom, close to the air whizzing under the car. I knew my welds were tight as I used my poor man's air compressor, the exhaust port of my shop vac, to pressurize the pipe while using soapy water. I had used my real air compressor over the years to check for leaks from welded on CATs but I discovered that the shop vac does plenty good in that regard and is much easier to use.

No pics of the welds will be forthcoming. Holy crap my welding is ugly. Strong enough but ugly I have a Lincoln MIG 220v, I think I need to try using some argon or the like instead of the flux core wire.

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1986 300SDL, 362K
1984 300D, 138K