Muffler failure that caused the floor fire.

[Bob Dunahugh]

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

 

[john r. lebetski]

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

 

[jesse farr]

That can cause some serious difficulties. Several years ago I had a BMW 750=
l that I had spent a small fortune on trying to make it nicer than new. A l=
ocal transmission shop had someone doing something under the vehicle. They =
pryed (pride ?) on top of the muffler causing it to dent in. Looking at it =
from beneath the car, everything looked perfect. Quite some time after that=
, after just filling up the tank and as I was driving down the road, the ca=
r all of a sudden started making a loud muffler noise. I was about a mile o=
r two away from a shop I use. I simply decided I would drive on to the shop=
instead to continue going home. About a few moments later, a car pulled be=
side me in the turning lane with the fellow driving screaming out the windo=
w telling me my car was on fire. I pulled over into a closed drive in area =
and by the time I got out of the car the whole back of the car was engulfed=
in flames. Learning that less than an undamaged muffler, no matter how sli=
ght, can be a very expensive lesson. That did not set very well with me.

I can only suggest that such underneath something with a wood floor would p=
erhaps be even less desirable.

jesse farr
soddy daisy TN
'74 26'canyonlands

Original message
From: "Bob Dunahugh"
To: gmclist;=20
Dated: 5/21/2017 4:52:52 PM
Subject: [GMCnet] 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 switch=
ed the mufflers from side to side so that the dent was on the top. So it wa=
s 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 t=
rip that was different. Then it hit me. I had heard some harmonics in the e=
xhaust 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 ba=
ck to two up front. Both have their positive points. I'm happy with what GM=
did. Bob Dunahugh
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[Bob Dunahugh]

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
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