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My truck has been making some kind of exhaust noise when cold and under load lately, and i wasnt sure what it was. Put it up on my buds hoist yesterday and it turns out that i have 2 broken manifold bolts, one on each side, and they are both closest to the firewall.

Why does this randomly happen?

Is this something that should be fixed right away?

One of the local exhaust shops told me that its common, and of no concern... its just annoying listening to it. They also quoted me about 1k to fix both
 

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Those two are the hardest to get to of course :evil: , not really a big deal to leave them it's just a little more exhaust noise. If you are anything like me, the second that you saw them you would have stuff tore apart and trying to get the broken bolt out at whatever cost, vise grips, drills, taps, whatever.
 

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There have been cases I have had where it will pull unmetered air into the exhaust causing the o2 sensor to detect a false lean condition causing an unnecessary rich fuel trim causing drivability concerns. Easiest way to get them out is weld a nut to the stud. Even if it's broken below the surface stick the welder tip in the hole and hit it with higher heat an build the tip out. It won't stick to the head because the head is aluminum and bolt is steel. It's easy peasy.
 

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Like GMrepairman stated above welding a nut to the stud is a good way to get a broken stud out and the heat from welding will expand the threads allowing you to back it out, another method which is the least desirable but we do it a work all the time at work is use a drill and the biggest EZ out that will fit in the stud to remove it but if you off center and you drill into the head now you looking at a thread repair like installing Heli-cols. Why does this happen metal fatigue plain and simple over time the carbon and other elements in the hardware cooks out weakening the studs add day to day driving and vibrations and the metal just breaks. Hope this helps.
 

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Man, what a rip off. I'd do the repair for you for $999, including parts. lol. Seriously, it's not an uncommon problem. Those bolts go through a lot of heat cycles and eventually it fatigues the metal enough that it breaks. The hardest part of the repair would be getting the old broken part of the bolt out of the head. You can check around to see if any of your local welders specalize in removing broken bolts like that. We have a guy around here that usually charges $75 to do it (after you have the manifold and other obstructions out of the way) and he comes to you.
 

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I just copied this from an eariler post i had....

I just did mine. '05 silverado 5.3 front and rear studs on the drivers side broken. First I PB Blasted the manifold to y-pipe bolts,waited about 10 min. (dis-connected the battery) then heated them till they started to get red. 1/2 inch impact for the accessable two, breaker bar with jointed extention for the PITA one(removed upstream O2 sensor for access) once those were off, i pulled off the spark plug wires(broke one ) removed the steering shaft bolt and let it lay on the frame. Loosened the unbroken bolts pretty easily with a ratchet and removed with air ratchet. Removed manifold from the engine comp. to workbench. pulled out the heat shield bolts and cleaned up the mounting surface.

Now for the broken studs.... I was lucky cause only the head was broke off, which left a little less than 1/2in of bolt sticking out from the head. Got a good set of vise-grips, and clamped them on as hard as i could. The front one came out very easy, the rear was a little more stubborn. then cleaned the head with mesh sand paper.

Put new manifold to y-pipe gasket on and set the manifold back in place. put on new manifold gasket on and lined up two starter bolts (m8-1,25x30mm). Put anit-sieze on and hand started all the bolts. tightened them all down, then under the truck i went.... once everything was tightened up, i put the heat shield back on with new bolts (m6-1,0x10mm) and over-sized washers. Replaced all the spark plug wires with new ones(AC Delco), reconnected the steering and battery. Started her up and she purred . Check engine light was out and I'm a happy guy. took about two hours plus clean up time. did the passengers side, almost same as drivers side, except all the manifold to y-pipe bolts are accessible without removing the O2 sensor. The oil dipstick tube runs thru the manifold and needs to be removed.

Dipstick tube broke trying to remove it :-x . Got it out by removing the starter and heating around it. No one had it in stock, so I cut off the jagged ends and used a 3/8 compression coupling as a temporary fix. Truck is all back together and running quiet

Also note that the y-pipe connection gaskets are different, drivers side has a round crush washer and the passenger side has a donut gasket.

I looked at my wife's 08 Tahoe and it appears that the process would be the same on the newer trucks.

I got Fel-pro gaskets and the metric bolts from Advance Auto.
 

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I know LMC has a "Solution" to this very common problem. It's just a small bracket that mounts to the head and then another bolt to hold pressure against the manifold to keep it from leaking. That might do the trick for you until you have time to fight with getting that bolt out.
 
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