Both Flowmasters came apart?

Grit dog

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Exhaust was pretty new looking when we bought the truck. After running it around now since sitting for over a year, developed a nasty tin can rattle. Hoped it was the muffler heat shields and had to take them off anyway so eliminated that potential. Exhaust rattles like hell once it warms up and actually sounds louder. Both mufflers sound like all the baffle welds came apart. Multiple clanking noises in both mufflers if you thump on them. Sounds like some of the baffles might be just laying inside the mufflers now.

What gives? They sound like they both spontaneously self destructed inside….
Been 20+ years since I bought hot rod gasser mufflers. Never had issue with Flowmasters before.
For all I know these are 20 years old, but they didn’t make noise before. And the truck hasn’t backfired or done anything to blow them apart.
First world problems I know…. But any ideas why they both just crapped out and come apart?
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pnwnvrdn

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"no backfire"
Without knowing the age of them, and the fact that they could be "20 years old", my guess is they rusted out internally.
A lot of condensation builds up, particularly if truck is used irregularly and/or short trips.
 

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^Good point. And makes sense. Most reasonable explanation anyway.
 

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We had a flowmaster on our Sub and the rattles inside of it were the guts of the catalytic converter that came apart.
Made it so we could not pass DEQ.

Not sure if this applies to your truck, but it might....
 

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Son drove it last night said it’s worse. Just fired it up again tonight and it sounds like a bag of fvcking empty soup cans getting blown around by a 3” dual exhaust.
Bad part is it’s fully welded and hangars were welded to the mufflers as well. And I’ll have to use longer mufflers or clamp them in with band clamps because they’re welded over the pipes all nice like.
 

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@Grit dog the issue may not be the Flowmasters at all. I had a similar situation with my Duramax recently and it was very difficult to diagnose. My 2500HD was down on power, the fuel mileage was down and there was a rattling noise in the exhaust.

Turns out I had passed a Ford so fast that wind going into my turbo had pulled the emblems off. I had little blue ovals plugging my air filter. I had Ecoboost and PowerStroke emblems ground up in the turbo housing. The rattling in the exhaust was a chrome goat head. The said my GMC must have eaten a Dodge diesel for breakfast one morning but the little "ram" emblem was so useless it would not digest.
 

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@Grit dog the issue may not be the Flowmasters at all. I had a similar situation with my Duramax recently and it was very difficult to diagnose. My 2500HD was down on power, the fuel mileage was down and there was a rattling noise in the exhaust.

Turns out I had passed a Ford so fast that wind going into my turbo had pulled the emblems off. I had little blue ovals plugging my air filter. I had Ecoboost and PowerStroke emblems ground up in the turbo housing. The rattling in the exhaust was a chrome goat head. The said my GMC must have eaten a Dodge diesel for breakfast one morning but the little "ram" emblem was so useless it would not digest.
While this truck did try to inhale a kitchen garbage bag once (fun fact, a 454 with a garbage bag over an open air filter will turn a 3" tall air filter into a 1" tall air filter in 1.234 seconds after it fires...) I don't think the kid has passed any Fords at a high rate of speed. At least I hope not, because the 15 year old tires only have 25psi in them and it has no shocks or steering stabilizer currently installed...LOL!
 

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Geeze Todd, that sucks. I'm sure with some careful grinder work and welding you can get it fixed without damaging the rest of the system. FYI if they are stainless Flowmasters they are covered by a limited lifetime warranty. Definitely worth giving them a call to see if they can do something
 

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Geeze Todd, that sucks. I'm sure with some careful grinder work and welding you can get it fixed without damaging the rest of the system. FYI if they are stainless Flowmasters they are covered by a limited lifetime warranty. Definitely worth giving them a call to see if they can do something
Thanks for the sympathy! Ha just checked that. They are not stainless. (although stainless is only $9 more now, probably $3 more when they were new??) And they have a 1998 date stamp. So now I know roughly when they were installed.
Good news is there's a good chance that the engine may have come out of a fairly new (low mile??) truck since it's a Vortec engine (no mech fuel pump boss) and presumably the mufflers were fairly new when the exhaust was done for that engine.

Bad news, they are definitely 20+ years old and likely been in service that long? Now it would be nice to know a little history and how much the truck was driven since engine swap (originally a 350 truck).

Man, I looked at trying to grind the welds off. Would have been 1000% easier before I re-installed the bed a month ago... Idk if I have the time or patience for that!
I'm tempted to take it to a good exhaust shop I know, but it's 100 miles away! Truck would make it no problem, save for not being real keen on pounding it 4 hours down the highway on tires that are as old as the kid driving it! But I'd get better mileage trailering it over with the diesel anyway!
 

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Instead of grinding the welds off, use a cut off wheel and cut through the flange of the muffler next to the weld without cutting through the exhaust tubing underneath. Whole lot less work this way...

If you have the time and money to take it to a decent muffler shop that's a solid option too, good luck!
 

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@CalSgt Great suggestion!
I was looking at creative ways of not destroying the pipes and was thinking of this. Then could zip a little slice off the new muffler flanges and weld them on right next to the old welds.
It’s more about having the time TO do it myself. Vs the amount of time to take it to a shop and pick it up.
I generally don’t trust shops and it’s a crap shoot to spend time taking it somewhere to find out they want $500 to rnr a couple mufflers. (Typical around here, everything costs twice as much. Not enough tradespeople to service all the non hands on people so they charge FU prices to everyone.)

I’m really considering pulling the bed off and just getting after it.
 

CalSgt

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@CalSgt Great suggestion!
I was looking at creative ways of not destroying the pipes and was thinking of this. Then could zip a little slice off the new muffler flanges and weld them on right next to the old welds.
It’s more about having the time TO do it myself. Vs the amount of time to take it to a shop and pick it up.
I generally don’t trust shops and it’s a crap shoot to spend time taking it somewhere to find out they want $500 to rnr a couple mufflers. (Typical around here, everything costs twice as much. Not enough tradespeople to service all the non hands on people so they charge FU prices to everyone.)

I’m really considering pulling the bed off and just getting after it.

I totally get it, no shop does a better job than you primarily because its your truck. I was strapped for time and took my jeep into a muffler shop to get welded up. They charged me $100, $20 per joint and they didn't pay attention to any of the alignment marks I drew so it doesn't fit quite right. The whole purpose for getting it welded was to keep it aligned because the clamps would let the pipes and muffler twist and start rattling.

If you do find the time I have a few ideas...

How hard would it be to drop the exhaust? Might be easier than pulling the bed, I'm not totally sure but at least it would be a one person job. Three nuts at the manifold, unbolt a few hangers, support the trans with a jack to get the crossmember out and it should drop down. You might not be able to get it all the way off if its a big one piece pipe but it would give you room to cut and weld. I built my new exhaust with V-band clamps so I can get it out without pulling the bed or cutting anything. Now would be the time to add them if you ever plan on pulling the exhaust again.

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Another option to make the cuts is an exhaust tubing cutter, i've almost purchased one for myself a few times but I get impatient and do it another way.

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