My ears are still ringing

[vectorit]

I just got my 1970 K10 back from getting a new exhaust system today, and went out for a spin to enjoy the latest upgrade to be done to the truck. The system is OE ram manifolds, dual exhaust with H pipe, and hemi turbo mufflers exiting behind the rear tires.

Truck sounded great! I could hear the engine, and everything else going on in and out of the truck. So I went for a little scenic route to get up to highway speeds, then pulled over to snap a couple pictures while the truck idled for a few minutes.
Hopped back in the truck, put her in gear and took off with a little bit of zip. As soon as I took my foot off the gas to shift... BANG! It sounded like a rifle shot fired from my cab out the window. Engine still running along, so I shifted into 4th and tooled along wondering what the hell could have caused that.
Then just as my ears are back to adjusting to some what normal noises, my exhaust sounded different...

I drove all the way home wondering what the hell let loose.

Well, as you can see both new mufflers with less than an hours worth of drive time on them are blown out and now have to be replaced.

Any ideas on what could be the cause of this?
I am suspecting my Pertronix II ignition may have caused this, so that is the first thing I am going to investigate tomorrow.

The truck runs great, and has never back fired like that since I have owned it.

[GASoline71]

If that was from a backfire... that was one helluva backfire! Holy cats!

Gary

[vectorit]

Originally Posted by GASoline71

If that was from a backfire... that was one helluva backfire! Holy cats!

Gary

Believe me, it was loud... hours later my ears are still ringing.

[cdowns]

with the price of gas now i'd think you might b money ahead by having your engine gone thru and tuned by a shop in stead of dumping it out the exhaust pip[e

[LockDoc]

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Sounds like raw fuel build up in the exhaust system but I would think it would have died if it was getting that much fuel while idling. Really weird...

LockDoc

[Classic Bowties]

Wow, didn't even get a chance to get a little mud on them. Talk with your exhaust guy and let him know you never had a backfire issue before the new setup, maybe the time to try a flowmaster or one of the flow knockoff types out? You could also drop fellow member Jerry Moss a message to pick his brain on the subject. Mel

[70cst]

[VA72C10]

Originally Posted by LockDoc

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Sounds like raw fuel build up in the exhaust system but I would think it would have died if it was getting that much fuel while idling. Really weird...

LockDoc

that's what I was thinking...

[shawno72]

Weld them back up and your good to go
Posted via Mobile Device

[Already Gone]

Subscribed, as I'm really curious.

[67c10rustbuket]

Cheap crimp mufflers? I saw a few blown and returned when I was a little man working at autozone.

[shawno72]

I wasn't going to mention the crimp mufflers, but since you did upgrade to a set of fully welded units ie flowmaster or magnaflow or the likes
Posted via Mobile Device

[special-K]

Are there potatoes in you pipes? It may just be cheap mufflers. I wouldn't blame it on being crimped mufflers. Millions of those (literally) have been under cars and trucks forever without blowing out. I've never seen one fail like that. But,poor quality is my suspicion since the truck runs fine otherwise.

[Classic Heartbeat]

My guess is exess fuel made it into the exhaust. I blew a muffler like that once with a big block. Funny thing was the motor seemed to run better after that.. WES

[Tom Vogel]

Originally Posted by Classic Heartbeat

My guess is exess fuel made it into the exhaust. I blew a muffler like that once with a big block. Funny thing was the motor seemed to run better after that.. WES

Yea Wes, sometimes when I have excess gas, a backfire makes me run better too.

[beautimus]

i did this myself, a long time ago on a ford ranger. i had replaced the timing belt and in the process of reassbling everything i had forgot to put the coil wire back on. i cranked and cranked and cranked on it. then i remembered that coil wire, i put it back on and was starting to crank on it some more, but just as i turned the switch something in the back of my mind said no!!, bu i let the key turn in my hand, the ignition fired and boom! sounded like a cannon went off. a dust cloud came up around the truck . the muffer had split lengthwise down the seam. the neighbors all came running to see what i blew up. it was that loud. The reason i am telling you is that the guys above have it right you were difinitly pooling unburned gas in the exhaust system, and thats what took the mufflers out. if you go down the road and turn the ignition to off for a few seconds and then back to run it will do the same thing, but not as violently. (don't try it with switch on the column because of steering wheel might lock) but i can't say what caused it.
best of luck. Tony

[rkn463]

I suspect a carb problem caused this. Some carbs (like quadrajets) have vacuum controled fuel mixture. If you've ever been inside one the primary metering rods ride up and down depending on how much vacuum you have, more vacuum - more lean. So if your carb works like that and the metering system gets gunked up you can get a situation where you run hard then let off the metering rods should slam shut but stick in the rich position which dumps a bunch of gas down the exhaust. Then you give it some throttle and blow a little fire in there and ignite the whole thing and BANG! It really sound like a rifle shot. I used to have an 80 model Ford p/u with a 300 six in it and it did this very predictably. So predictably that it was loads of fun. Now I'm not saying that I ever made it "shoot" at a motorcycle cop under a bridge but I'm not denying it either. In that truck after I blew out the old rusted stock muffler I had Midas put on one with a lifetime guarantee and it never blew out.

[vectorit]

Well, this morning I go out to take a look at things.
Nothing out of sort that I can see, other than a destroyed pair of mufflers.

So I hop in the truck to take it to my friends shop, and notice the clutch peddle seems light.

So I proceed to go down the street, and get a couple blocks and the truck jerked hard after shifting into second. Then I notice the clutch peddle even more light.

Get to a stop sign, and it lets me put it into 2nd but at this point I am thinking I am not going to make it through the intersection. Just then as I let the clutch peddle up to move forward, it jerked hard and stalled the engine.
At this point there is no pressure feed back on the clutch, and luckily I am on a hill so I let it roll back to the side of the road.
Open the hood, and the clutch linkage is fine with nothing looking out of the ordinary.

Call the tow truck and have it towed to the shop, and now I am waiting for the damage report.

At this point I am so mad I can barely see straight.


As for the votes for raw fuel collecting in the mufflers - I have to agree with that assessment.

Though I am perplexed as to how that can be, since the exhaust doesn't give off the smell of raw fuel and there is no black smoke. The plugs were just out to be inspected, and all of them were a light chocolate color showing a good burn.
The carburetor is a new reman Q-jet from Jegs.
The plug wires, cap, and rotor are all new.

The only thing that was not right about the truck was that it was gutless at WOT, to where the secondaries never really seemed to open up and give you a the feeling of the engine pulling hard. Low end power is great though.

The plan was to get the exhaust system done, then head over to my buddies shop to diagnose the weak performance at WOT. Since the old exhaust system was headers, and worn out turbo mufflers along with much needed new ignition components.

[special-K]

If you had intermittent power to your ignition then it could cause a backfire. But,you never heard a backfire,right?

[67ChevyRedneck]

Holy crap. NEVER have I seen mufflers do that!

About your clutch... weirdest thing that ever happed to me with the 67 was that a flywheel bolt actually backed itself out and got hung up in the clutch not allowing it to release. After playing with it for a while I heard a REALLY LOUD BANG and it worked again... The bolt actually almost blew a hole in the bottom bellhousing cover (the thin metal piece that bolts on). It left a hexagon impresson and a half tear mark where it almost went though. Wish I had kept it...

[vectorit]

Just got back from the shop, and the transmission/transfer case is coming out.
The clutch is gone, but I didn't see anything broken while it was up on the rack.

Luckily my buddy knows the exhaust shop guy, and so next week he is going to show him the carnage. My friend who owns and operates a shop, is shocked to see this happen in such a short period of time (less than and hour on new mufflers, and the truck never backfired like this before).

I will know more next week.

[treveiger]

Wow, that's insane!
Posted via Mobile Device

[67c10rustbuket]

I didn't mean that all crimp mufflers are cheap crap, just maybe you got a bad pair. Working in a factory I know the first few parts made at setup may be "good enough". The gas pooling issue seems to be the most logical. I'm curious to see the result. Later

[vectorit]

Originally Posted by 67c10rustbuket

I didn't mean that all crimp mufflers are cheap crap, just maybe you got a bad pair. Working in a factory I know the first few parts made at setup may be "good enough". The gas pooling issue seems to be the most logical. I'm curious to see the result. Later

That's what my buddy at the shop was saying, in regards to raw fuel collecting in the mufflers.
He is concerned that they may have been defective as well, and is going to call the guy that I had install the system over to his shop to show him.

[vectorit]

Update:

Transmission/T-case are out, and the pressure plate appears to be broken inside. It's a Borg Warner brand, and only has about 4 thousand miles on it.

Clutch disc and fly wheel still look new.

Didn't have my camera, but I will take a picture of it and post. But, unfortunately you can not see or hear any damage to it. It is like the diaphragm connection inside has broken, and they don't allow the pressure plate to lift when the pedal is depressed.

Strange how this goes out at the same time of the backfire incident.


Muffler shop is not going to do anything about the cost involved to replace the mufflers either, since something apparently with my ignition caused a premature ignition to cause the back fire.
I have had multiple mechanics look at the truck, and assess how it is running and all of them pointed out that it is not running rich.

Once the clutch issue is resolved, we are going to dig into the ignition system.