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[GMCnet] Muffler failure that caused the floor fire. [message #317830] Sun, 21 May 2017 15:52 Go to next message
BobDunahugh is currently offline  BobDunahugh   United States
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Registered: October 2010
Location: Cedar Rapids, IA
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John. Finally put the puzzle together. When they moved the burned GMC from the side with a large fork lift. They put a dent in the bottom of one of my new mufflers. I removed that new exhaust system from the burn GMC. To put it in the replacement 78 GMC. When I installed the exhaust system. I switched the mufflers from side to side so that the dent was on the top. So it was out of sight. One night I got to thinking about why the muffler fractured. ( Back to things that drive me Crazy. ) And what had transpired on that trip that was different. Then it hit me. I had heard some harmonics in the exhaust system at some RPM, and load ranges. So that's what had to have been the reason the muffler fractured. And broke apart. As to one muffler in back to two up front. Both have their positive points. I'm happy with what GM did. Bob Dunahugh
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Re: [GMCnet] Muffler failure that caused the floor fire. [message #317851 is a reply to message #317830] Mon, 22 May 2017 10:01 Go to previous messageGo to next message
JohnL455 is currently offline  JohnL455   United States
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Registered: October 2006
Location: Woodstock, IL
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It's always good to be smarter than the problem. Gives you some satisfaction solving the puzzle. And good to know the inexpensive NAPA muffler are still a viable choice. Makes you wonder about the GM factory modified mufflers (they bashed in the corners on certain Corvettes and the Buick GNX for
clearance.). I guess the corners can take a dent whereas the flat areas may start to "oil can" and flex fatigue as yours did.

John Lebetski
Woodstock, IL
77 Eleganza II

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Re: [GMCnet] Muffler failure that caused the floor fire. [message #317856 is a reply to message #317830] Mon, 22 May 2017 11:41 Go to previous messageGo to next message
BobDunahugh is currently offline  BobDunahugh   United States
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Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
Senior Member
Jesse. Thanks for telling us of your fire event. And you had a steel floor. Hopefully our fires will make owners more aware of this unseen danger. GMC put that heat shield between the tail pipe, and gas tank for a good reason. So how many owners have checked their shields out? ( Jim K at applied sells them. ) Mine were in. Plus now I've added a large heat shield between my mufflers, and floor. It's 1/8th inch aluminum with a 1 inch gap between the shield, and the floor. A side benefit is that the floor will be cooler. As a note. I don't know when GMC covered the underside of our floors with aluminum. My 78 had it. And still BURNED. Think about your floor. Bob Dunahugh 78 Royale.


________________________________
From: Bob Dunahugh
Sent: Sunday, May 21, 2017 3:52 PM
To: gmclist@list.gmcnet.org
Subject: Muffler failure that caused the floor fire.


John. Finally put the puzzle together. When they moved the burned GMC from the side with a large fork lift. They put a dent in the bottom of one of my new mufflers. I removed that new exhaust system from the burn GMC. To put it in the replacement 78 GMC. When I installed the exhaust system. I switched the mufflers from side to side so that the dent was on the top. So it was out of sight. One night I got to thinking about why the muffler fractured. ( Back to things that drive me Crazy. ) And what had transpired on that trip that was different. Then it hit me. I had heard some harmonics in the exhaust system at some RPM, and load ranges. So that's what had to have been the reason the muffler fractured. And broke apart. As to one muffler in back to two up front. Both have their positive points. I'm happy with what GM did. Bob Dunahugh
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Re: [GMCnet] Muffler [message #318197 is a reply to message #317830] Mon, 29 May 2017 21:53 Go to previous message
BobDunahugh is currently offline  BobDunahugh   United States
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
Senior Member
Jack. To get your aluminum sheeting up. I used a 2' by 2' piece of plywood with a1' 2x4 centered on end to the plywood. then a floor to raise the plywood. The aluminum centered itself nicely. Then heled the sheet in place with some 1.75" wood screws with large fender washers. Then a sheet of 1/8th aluminum, 2' by 4'. Screwed the panel to the floor with 6 - 3/4" spacers to make an air gap between the floor, and heat shield. Bob Dunahugh


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