I got rear ended and the exhaust pipe was mashed forward causing the crack in my Catalytic converter's weld. Or perhaps, it just worsened the crack if it was too small to notice before. The crack does NOT go all the way around. I have not had a CEL appear and have had the crack for 1k+ miles.

To me, the crack appears to be in a spot that could be welded. I am looking for suggestions from folks with exhaust work experience, what is the most sensible approach to fixing this crack? Obviously, the goal is to avoid replacing the otherwise healthy cat. Thanks:enter image description here

I am thinking, at minimum, a few spot welds would stick. I could then use a patching material of some sort? Ideas?

  • Why not just run a new bead around it and repair it? – Pᴀᴜʟsᴛᴇʀ2 Mar 7 '17 at 0:32
  • @Paulster2 shop was concerned about burning a hole through the sheet metal. Think I just need to find a more experienced welder and/or with better equipment? – justinm410 Mar 7 '17 at 6:07
  • An experienced welder should be able to seal this up without any issues. I've done it before and I'm not anywhere close to what I'd call "experienced" ... I muddle through and get metal connected together. With as small of a crack which is there, it's more of a seal than a structural weld. It just seems a weld would be more resilient than putting some kind of patching material (I'm think you are talking about a high heat JB Weld or something similar). – Pᴀᴜʟsᴛᴇʀ2 Mar 7 '17 at 14:11
  • Not sure why you wouldn't hand this off to the insurer of the car that ran into the back of yours? – Steve Matthews Mar 15 '17 at 16:58
  • @Steve Matthews Because several months ago they told me to stop calling them. The next step is legal action which wouldn't be worth it for < $300. cough cough Allstate. The shop that did the work "guarantees" the quality, but they also told me they didn't "want" to work on it anymore (Mercedes) and I don't trust their work for obvious reasons. Insurance claims, man, you just never win. – justinm410 Mar 15 '17 at 17:20

I took it to an auto exhaust shop that is well known (according to reviews) in the area for their skilled welding work. They lowered the exhaust and sealed up the cat's crack with no issues for $170. In fact, they knew it was the catalytic converter before I even told them. Apparently, it is common issue on the Mercedes W211 E-Class cats.

Unfortunately, there must also be crack in the manifold. So, junk yard parts are on the way for that, as well. Not quite ready to take the plunge on the aftermarket options.

Takeaways- getting hit from behind can really mess up your exhaust and if something doesn't sound right after a repair, it probably isn't right. Oh well.


It looks like there are two joints that are cracked there, the smaller one that connects to the pipe looks cracked too?.. I'd have the cat/pipe removed and tig welded. With tig you should be able to use minimal filler material and end up with a more original looking finish.

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