Any Idea What's Going On Here?

[Tom Evans]

I have been chasing down an elusive noise in the vacinity of the center muffler/resonator of my wife's 1981 300SD. I replaced the exhaust system with one from Pull-a-Part. No improvement. I decided to cut the center mufflers open to see what I could see. The left muffler looked normal - full of insulation and a lot of carbon. The right muffler surprised me in that there was absolutely no insulation in the main compartment on this muffler!

Was the insulation left out on purpose or was this a manufacturing error where Dieter and Hans were having a bad day?

Thanks.

[eatont9999]

Those are supposed to be resonators. Perhaps they are each designed for a different sound frequency and work together to eliminate high and low sound frequencies. Can you post a picture of the other one?

[Delibes]

Buffalo Springfield - For What Its Worth


There's something happening here
What it is ain't exactly clear
Getting so much resistance from behind
I think it's time we stop, hey, what's that sound
Everybody look what's going down

[jackson101]

Perhaps one is an "after-market" unit. The lack of material, is just what you might expect from an aftermarket item like that.

[dude99]

perhaps the baffling material disintegrated and got blown out over the last 30 years?

[Tom Evans]

Let me address your comments. Attached is a photo of the complete exhaust system. A single pipe comes from the exhaust manifold. Near the center muffler/resonator the pipe divides in two going to each meffler/resonator. The outputs of the two mufflers/resonators go back into one pipe and on to the rear muffler. After removing to old insulation, there is no way that it could have disintegrated over the years and been blown out of the system. The date stamps on the center muffler/resonator indicates that it is the system than came with the car, not an aftermarket unit. The two original posted photos are photos of both the right and left mufflers/resonators before any insulation was removed.

[Zulfiqar]

was the sound like a leak?

Im wondering if the W124 centre resonator also is a glass pack - my car has a strange leak sound that no shop can remedy.

[Tom Evans]

The sound I was chasing sounded almost like a knock or rap. You could hear it plainly when you have the rear seat bottom removed. It occurred only in a very narrow RPM range and would often (but not always) occur while moving or sitting still. I checked everything under the car to see if anything was hitting together. I have an almost identical car (1982 300SD) which doesn't have this problem.

A good way to determine if your resonator is an absorbtive muffler (i.e. glass pack) is to look at the input and output pipes. If they are in a straight line, you probably have a glass pack. A non-glass pack muffler usually will not have its input and output pipes in line since this muffler has offset chambers to muffle the sound.

[Zulfiqar]

Originally Posted by Tom Evans

The sound I was chasing sounded almost like a knock or rap. You could hear it plainly when you have the rear seat bottom removed. It occurred only in a very narrow RPM range and would often (but not always) occur while moving or sitting still. I checked everything under the car to see if anything was hitting together. I have an almost identical car (1982 300SD) which doesn't have this problem.

A good way to determine if your resonator is an absorbtive muffler (i.e. glass pack) is to look at the input and output pipes. If they are in a straight line, you probably have a glass pack. A non-glass pack muffler usually will not have its input and output pipes in line since this muffler has offset chambers to muffle the sound.

hmm - I also have that rasp, tinny sound problem between a 500 rpm range, no leaks, checked with hammer, no loose bits, the only remaning bits are the mufflers.

[LNGfish]

Tom,

I had the muffler-fellow put what "you call" a glass pack smack in the center area to replace the paired resonators; L and R. The inlet and output were in line so I am calling it a glass pack,as u described.. ID's/OD's were same so I figured no restriction. That was 3 years ago. I think it cost $30 plus labor. It was bout 12-14 inches long and about 3-4 inches in diameter. It isn't that much fatter than the pipe so easy to install but you have to pay attention when you locate it with driveshft there. This is easy at shop on lift.

Then I purchased 2 cut lengths of steel flat bar at ace hardware and we used these "to tack weld to main pipe" (on top), and these reached out left and right to connect , "with a tight bent loop at end", to the Square rubber hangers on the sides of the car. You need this to keep the pipe from swaying left to right. You must do this.

Ace hardware has these precut flat bars in 4 foot lengths. I want so say they were flat bar 3/8" wide or 1/2" wide, BY like 1/8' thick. I think the cost was $6 each, times 2. Grab some primer paint and spray them if you want, I forgot to to this.

If you find anything else as "source of noise", since I have 5-10% left still let me know!

I can tell you one thing for sure:

The car is "much quietier" now at 70 MPH or so with the "rear muffer" renewed eventhough it looked fine and no holes. What I did at center area had little affect but I wanted not to remove the center muffliing entirely nor purchase new at $300-$400 this center assembly so I put something back there for a little cost.

Amazing mine still had the original muffler on it, but it sure was shot on the inside and I didn't know it.

I still have some of the rasping sound at low RPM under load but it goes away but nothing like I had before. Good luck.

Steve

[tyl604]

I believe the muffler system on the 126 was designed to move. Check out the use of rubber hangers; I know they are at the rear and seem to remember that they support the muffler/resonators too at the center of the car. So would not your flat bar and tack weld remove this engineering design? But I still do not know what movement is supposed to accomplish when it comes to the muffler system.

[Tom Evans]

Perhaps I wasn't clear enough in my first post. The photos in the first post are of the same center muffler assembly. There are two chambers, one on the left and one on the right. The left chamber was full of insulation. The right chamber on the same muffler assembly was missing almost all of its insulation. It is a Gilette muffler and it is the muffler installed on the car at the factory.

[LNGfish]

Tom,

I had this sound I think you are describing. I removed the 2 center resonators and 80% of the sound went away. Then I still had 20% of the noise so I renewed the rear muffler assembly. All this over a 3-4 year perios, not all at one time.

Now it is very faint but still there 5%-10% but allot better than what I had at beginning.

All my resonators where original and so was rear muffler.

It is a very annoying sound I agree.

Good luck!

Send me an email or private message if you find anything else. Thanks!

Steve

[LNGfish]

I believe the center muffler hangers are there to support the center mufflers from a left and right movement and less verticle support. I had heard of allot of folks who had also removed the center mufflers alltogether. The flat bars are still rouuted the the original rubber hangers so there is ample movement L to R but less verticle support as orginal.

[oldsinner111]

I removed all mufflers the turbo is a silencer itself