Posted by New 1500 Z71 on August 16, 05 at 12:45:11:
In Reply to: Exhuast rumble under the hood posted by KCBurb on August 16, 05 at 11:49:18:
: Drove the burb home from work yesterday and all was well. Got back into it after it had set for about 30 minutes and it suddenly had an exhaust grumble under the hood. Passenger side. Is more noticable when you step on the accel. . . Manifold crack on me?
Not likely. The doughnut seal is done. ~$5 each from the aftermarket and you should replace both at the same time as you need to loosen the Y-pipe from both flanges to service either one. GM has a bulletin out that says to grind the flange stands (the legs on the mating flange) 1/8-inch shorter than they came from the factory for better sealing. This can be done on-vehicle once the Y-pipe is loosened and dropped a little bit. Make sure you sit the replacement seals square into the manifold before bolting down (I say this because these seals aren't just a doughnut, but are affixed to a little inset pipe. Also, coat the studs with anti-sieze before threading the nuts and tighten, and then torque to specification, evenly across each of the three bolts per flange.
: Also, I was reading on #1 Son's page that there is a joint at the Y pipe. So I won't have to do any cutting or welding?
No welding, no cutting, but a little grinding as I indicated above.
: If I should break a bold - can they be drilled out?
No need, they are threaded studs. Soak the nuts and threads with PB Blaster or Liquid Wrench a couple of times the day before you go at the repair. Use a 1/2-inch drive hand ratchet or flex handle (NO AIR RATCHET OR HAMMER or the studs will shear right off) with some long extensions and a deep hex socket (not an 8 or 12 point socket). They should come off with the stud intact. If not, and one breaks it'll shear below the manifold side flange per their design. Soak the broken stud's threads through the mating hole on the 'top' side of the exhaust manifold flange, rap on the borken end a few times with a ball-peen hammer and flat punch to shock it loose, and then spin out the broken stud with vice grips firmly clamped to the broken end. I can tell you that unreputable repair shops purposely yuse air tools to shear the studs so they can charge for the removal of the exhaust manifold and replacement of the studs, which is labor intensive.
: If I don't mind the noise - how urgent is it?
Not terribly, but it will get louder and fumes may start to escape into the passenger compartment. If the doughnut material has broken away, it can allow the joint to move and this will take its toll on the hardware making your repair tougher. So if you hear a metal on metal sound, fix it sooner rather than later.