Repair or Replace? (Exhaust pipe crack - [Photo])
 

I lost an exhaust hangar which caused my exhaust pipe to flex over and over, and a crack occurred just ahead of the center muffler/resonator.

It is cracked at the weld but not rusted through, so I would think it can be welded.

Black residue on bottom/front of resonator is blown-back oil from a timing cover leak.

Photo Did not Attach in First message. Here it is.

Mine developed a similar crack and the local indy muffler shop welded it for $20.

Great -- thanks.

I am finding the muffler shops are saying "replace," whereas indy repair shops and independent welders are saying they can probably re-weld it.

All depends on how thick the remaining metal is, ... usually it'll burn through quickly if it's rusted thin and thus can't be welded.

I have used PC-7 to patch the same spot on my exhaust. It works very well.

Metal thinness was the concern of an indy boiler welder who I asked about it, and may be able to help. But tomorrow morning I will be taking it to a local Chevron station that does welding, and who believe they can fix it. If they can, I will let them.

Welding is a weird science. It could depend on the alloy(s) there.

You might post that photo on http://weldingweb.com and see what the alchemists there say. You could post under General Welding Questions or Mechanic's Park.

I had not heard of that -- but just Googled it.

If I am unable to get it welded I will use that or Permatex Metal repair epoxy, and then secure a thin pipe clamp over it to keep it from blowing out.

The muffler is only a few years old, is a genuine MB part, and I cannot come to terms with throwing away something that is perfectly good.

I also saw that both tailpipe hangars are broken, as if cut. Considering the thickness of the rubber, I am having a hard time accepting that the weight of the muffler could have broken both of them -- or is that common?

Thanks! :2thumbsup

The PC-7 works without any clamps. It is like silly putty when you mix it and you can work it into the cracked area enough so it grips really well. Let it dry overnight if you end up using it. It will probably be stronger where you repaired it than the rest of your exhaust.

OK. Is is heat resistant? And where do you buy it?

I taped thin strips of Gorilla Tape Around the periphery of my broken hangers, and am about to reinstall them. That should at least relieve the stress on the crack tonight, and during my drive to the dealer to get new ones.

It seems to be heat resistant. About 4 months ago, I drove over a metal cover at a car wash that was not properly secured. The cover came up and hit my muffler, cracking both exhaust pipes where they go into the muffler. I have used it successfully in the past on my 400E exhaust as well.

You can buy it at Ace Hardware for about $15.00. You have to mix the two compounds with a putty knife. After the repair, you will smell the epoxy for a few days after you park the car when it's hot, but the smell eventually goes away after a week or two. I can't believe how strong the PC-7 is.

I've been reading the reviews and everyone seems to love it. My only worry is that it is temperature rated to 200 degrees F, but if you have been using it successfully on your car, with a larger and presumably hotter exhaust than mine, I'll try it.

Also, I am seeing PC Fahrenheit, specifically designed for high temps, however, that is a hand-moldable putty which I expect may not be as strong as the PC-7(?)

I have used PC-7 with good results in the past. Unfortunately in my state, Pennsylvania, they visually inspect the exhaust system and failed my car due to the patch.

I had a sleeve welded over the break which was acceptable for the state inspection.

Those rubber hangers break; that's just the way it is. Order some over the internet with a couple to spare and keep an eye on your muffler and pipe.

I actually could not get them back on. Luckily, I save all the o-rings that come with my oil filters so, in place of each hanger, I doubled-over four o-rings (to make the diameter smaller) and used them to hang the muffler. Around each set I also tightened a hose clamp for good measure. Should hold just fine for the day.

The PC-7 seems to be the easiest, definitely the strongest, and will go on smoothest. I also considered putting a ring of PC Fahrenheit around it, or would that be unnecessary?

Curiously, the day after I began hearing the exhaust noise I had the car inspected and is passed with no problem. It's possible the crack was much smaller, or simply not visible from the angle the inspector was viewing the exhaust system from.

I will be having it looked at by the welder shortly. If he cannot do anything, I will go this route. Now that the muffler is secured again, I am not worried about further breakage, but will inspect everything between the resonator and the cat in case something else was damaged.

OK, what is in the photo can now best be described as a hole. An actual narrow crack runs around the other side of the pipe about 2/3 of the way down. Can't be welded because of the rust, but can be sealed. There is also a sleeve within the pipe which can serve as a convenient substrate for the sealing material. From the resonator to the engine, the exhaust is solid.

I looked for PC-7 but was told at Home Depot the company no longer manufactures it. (They nonetheless still have some on their web site.) He said they are moving towards the more universal putty-type products, like PC Fahrenheit, which they did stock and which I purchased.

I also stopped at Autozone for a patch kit so I could scavenge some wire and refractory fabric from it. The plan is to scrub down the pipe, wrap a narrow strip of fabric into the crack, then some wire, and then ring that with the PC Fahrenheit at approx. the width of the gap at the top. As long as the rear muffler does not bounce, it should hold. But if there is flexing, all bets are off and I'm looking at a replacement.

I also picked up new hangers from the dealer. According to them (HBL in McLean, VA), MB is now using the round donut rings for my car. Since the oval/crossmember units are available in AllPartsExpress, I doubt that assertion, but since they were only $2, I won't complain. Also, because I intend to keep those hose clamps around each hanger to make sure they do not flex, the round ones are actually preferable.

EDIT:
Seems the patch kit also contains some foil. So that will go on first, then the fabric, the wire, and the PC.

I'd go find another welder. A gennie MB muffler is worth saving, and the right way is to get it mig welded. If the metal is not too thin, the rust can be removed with a wire wheel on a minigrinder and the hole/crack filled in several passes using low heat setting. Or, simply cut out the bad part and weld in a replacement piece of pipe. This kind of work should be duck soup for any competent muffler shop IMO. I've done this kind of repair many many times, and on parts way worse than the piece you pictured. PC7 or JB Weld or whatever will not last because of the flexing, so I wouldn't waste my time. This kind of repair is best done at the bench with the piping off the car, but it can be done on the car with some patience.

Based on what you said, I called another shop who said they could replace the "D Pipe" and clamp it (they don't weld). Does that make sense?

There isn't anything to clamp onto... I think you will get a different answer when they see it. I agree the epoxy stuff will have issues with thermal expansion cycles. You would want the biggest gob possible. And if you have state inspection where they look at the muffler it won't pass.

donbryce gave the kind of answer you will get on the welding site. These guys are scientists. They have to learn all kinds of metal chemistry stuff. They don't explain it that way but that is what it is about. Yes a good weldor (person) can fix it. A bad weldor can screw it up.

I used to live in Fairfax BTW.

Yep, they had a deer in the headlights reaction when I arrived at the shop and described to them what I needed.

Somewhere in Manassas, there is a guy (or gal) able to weld a replacement pipe and I'll take my search there since I won't get any satisfaction from the corporate shops around here. :) In the meantime, I'll form a temporary fix with the PC Fahrenheit.

Heat and mechanical flexing is a big concern, and part of my motivation for doing the foil-fabric-wire layer was so the PC-Fahrenheit would kind of float on top of that, with just a portion of it adhering directly to the metal. I conjectured that a ring of this type would not need to seal the leak entirely, but just block enough exhaust gas to eliminate, or significantly reduce, the noise. (The pipe has been cracked for a long time, but I only began to hear it last week, so some escaping gas is not a noise problem.) Also this should make it easier for the welder to clear the epoxy away.

What part of Fairfax where you in?

You are wasting your time and money, doing a patch job. A good muffler shop - a good welder - can take out the section of nasty pipe you have there and replace it by welding it directly to the good muffler and to the existing pipe before the rusty part.

Replacing MB muffler hangars is much easier if you support the muffler in place with a small jack.

I realize that, and that is my intent. But first I need to find the shop/welder able & willing to do it. So far, I've been striking out, so in the meantime I will do the patch to keep things quiet. I d not expect it to be permanent.

My knee works pretty well also. :D

Greenbriar. If you know where that is.

I sure do. I used to date a flight attendant and passed Greenbriar a lot on my way to and from Dulles. I still get out that way quite frequently.

Aahhh... Delightful silence. :)

I have a ring of PC Fahrenheit over the crack. (Installation: Thin layer of PC Fahrenheit; foil strip; then successive rings of PC.) Smoothed and shaped, it looks like a slight extension of the neck of the muffler. If painted gray, you would likely not know it was there. Should last long enough for me to find a welder.

An old Bean can and two muffler clamps.

Cut the can lengthwise (after removeing both top and bottom) then wrap around the damaged area and muffler clamp away.

Nice job - for the interim.

The picture shows the crack is at a weld area. Stainless steel exhaust systems are prone to cracking from a phenomenon called "sensitization". This results in stress corrosion cracking and is a common failure mode for stainless steel exhaust systems, and universally occurs at welds.

Resistance to this type of cracking is dependant on how the supplier fabricates the exhaust system. Unfortunately, there is no way for the manufacturer to determine the quality of the fabrication and how sensitized the welds are until it is caught by their warranty system and a laboratory investigation is performed. I've done a lot of laboratory investigations on this exact phenomenon.

And two broken exhaust hangers accelerate the cracking process. :)

I may end up just replacing the resonator. Seems the simplest of all options.

Another compelling reason for a replacement, or a solid re-weld, is exhaust
back pressure.

I'm definitely noticing the performance gain. Nothing dramatic, but definitely noticeable.

Revisiting this after almost a year.

The epoxy fixed worked -- for a while. I would say a week at most. The epoxy ring stayed on the pipe but the seal did not hold so exhaust gas reseumed leaking, but the noise was not as big an issue.

More recently I removed the epoxy -- easily broke it off by hand (proving how ineffective it was) and did the tin can thing, sort of:

* Cut a 1/2" ring from a bean can.
* Coat inner radius with Permatex Copper gasket maker
* Wrap around cracked part of pipe
* Secure with exhaust clamp.

This will likely be a more permanent solution. I say likely because I am now thinking I should have let the Permatex solidify on the 1/2" ring before attaching it to the pipe. I may yet still do that and am preparing one in the likely event that I do.

Your best bet is to get a piece of sheet metal thicker than a bean can. Clean the area and bend the metal around or whatever necessary to mold it to the shape of the leak. Then MIG it in place. Surely you have a friend with a small 120 Volt MIG welder.

Since the leak was originally due to flexing and not from a rotted pipe, a patch will work fine.

I have a MIG welder and a stick welder. I've done enough sheet metal welding with a stick, that I can use a 5/32" 6011 rod and just stick weld it. If you find someone to weld it with whatever they feel comfortable using, you can fix it once and for all.

I've got the same problem so this is timely. I'm not expert but why can't a welding or muffler shop remove the parts, cut off a few inches of the pipe going into the muffler, then weld a new piece of exhaust pipe where the old pipe was cut and weld the other new piece of pipe into the muffler? This was suggeted earlier. I don't see what the big deal is unless there is a problem removing the offending part from the car. I'll let you know what I find out.

Yes, a muffler shop can indeed do this. Anyone who can weld sheet metal can do this.

Thanks, I'll see who I know who has that skill and equipment.

And -- rubbing my eyes -- Larry Bible? I thought you left here several years ago? Welcome back. :)

Id weld it. Even if rusty, it will just burn back some, no big deal, fill it like a rosette weld if it burns open some. Fixed plenty of stuff like that. Worst case a patch weld over it or section and replace a short piece of pipe.

You epoxy patch lasted a week and you lived with the hole for a year, then recently can patched it?

Have you thought of asking a muffler shop to remove the resonator all together and just keeping the rear muffler? People have done this without affect to emissions and I doubt a smog guy will notice.

Sure did. The leak did not sound as bad and I did not drive the car very much.

The resonator should not be removed because the engine is tuned to operate with a certain exhaust back-pressure. This becomes immediately evident when a small leak is sealed, i.e., no more upshift delays or doggish performance.

Where did you hear this? I think the ECU / O2 sensor would compensate. What happens when the muffler and catalytic converter degrades over time? What do you think happens when aftermarket mufflers for W124 with different back pressures are installed? The trans is also tunable for shift points.

When I asked a tech (Silver Star Motors, Vienna, VA) about possibly eliminating the resonator, he told me that.

I don't know if the cat and muffler degrade to the point where back pressure is affected, but I am sure someone will chime in with that answer.

Following up on this, here is what was true:

You do need thicker metal than a bean can, which is too thin and will deform under the pressure of the exhaust clamp, vibration and exhaust system flexing ( and leak al over again).

I noticed noise from back there about a week ago and replaced the thin metal with a thick, stiff ring of copper cut from a pure copper goblet that was given to me as a gift (that I have no practical use for). Applied the Permatex Copper to it, wrapped it around the pipe, clamped it down and so far, so good.

Nonetheless, I want it re-welded but still have not found a welder but will ask about it when I take the car for inspection.

Another FYI for anyone coinsidering this patch:

If you clamp or otherwise seal the leak and a short time later you hear the exhaust again, so you undo/redo it but once more, a short time later you hear noise again -- and this happens, say, 3 or 4 times with the "fail" time occurring more rapidly, check the adjacent pipe to see if it also has a crack or hole and if so, seal it.

This did not nececessarily happen to me; I'm just sayin"... :rolleyes:

To bring closure to this thread, I had the center muffler replaced today after my leak/loss of power returned some weeks ago. (I purchased an aftermarket steel muffler online and brought it to a shop for installation.)

I was surprised to learn that I had the original factory exhaust -- with the center/rear mufflers as one piece -- so cutting and welding was done.

Mercedes exhaust are made of strong stuff since the shop went through three blades making the cuts. The new center went in seamlessly and I actually like the smooth lines from cat to rear muffler, with no flanges.

When the old center came out, the pipes into it (where my fix was done) were loose and wobbling. Although the temporary fix protected the outside, rust and continued flexing still broke down the interior.

So, I once again have quiet exhaust and full power. :)