98 chevy 3500 exhaust leak

my truck has a exhaust leak at a large flange between the 2 cat converters right under the passenger seat. does any one have experience fixing this issue? i put a new gasket in it this spring but i could see light through the seem when i had new gasket in and the 3 bolts tight, so i took it back apart and put the original 24 hour cure jb weld on both sides of the gasket and put it together with that on it. let it set for 24 plus hours before using it. it worked for a little while but is pretty well all blown out again now. does any one have a good way to fix this issue more permanently?

i thought about cutting off the 2 flanges and splicing it all together with pipe but the pipes have such a large size difference and the one cat is basically welded right to the flange that i couldn't think of any good way to do that.

i could try just jb weld and leave the gasket out and see if that would hold?

i also picked up high temp jb weld i could try but it has a lower temp range than the original jb weld that i used the first time around

im pretty sure that 2 gaskets will never fill the gaps and the one auto mechanic i talked to said that wont last either.

would like to get it fixed, i couldn't believe how quiet the truck was after i got it sealed up this spring.
 
Stove and furnace cement in place of the JB weld will work, at least for a while.
 
I don't think stove cement will last long because its only good to a little over 1200 degree and you said it was bolted up close the cat converter and they run from 1200 to over 1600 degree .
 
we will find out, i just finished doing it. the stuff i have claims its good up to 2000 degrees, we'll see. i also got some exhaust tape and wrapped that around the seam after i bolted it together and filled the seam with the cement, then i took a big hose clamp and put that over the tape centered over the seam.

i have my fingers crossed. if it don't work i'm only out $20 and 2 to 3 hours of my time.
 
Is the exhaust system under your truck made of stainless steel?My 1997 GMC still has the original exhaust and it is all stainless steel.
 
I'm pretty sure its not stainless, my magnet sticks to it pretty good. it is in good solid shape though considering the amount of rust on the rest of the truck, must have something in it to prevent rusting with out the cost of stainless. I don't know why I put 98 the truck is really a 96
 
Some types of stainless ARE magnetic. IMHO, if you were to try welding on it with normal rods or wire I don't think it would go well.
 
My wife van leaked at the same place. Drove to the muffler shop they cut the flange out both pipe pieces and welded a piece in. Took them about 15 minutes. I had an oil change done at the same time. Total of 30 minutes paid $80 and was on my way. Exhaust isn't worth fixing your self unless you have all the equipment supplies and do it every day. I did the same fix on my car at the farm shop when I broke it on a holiday weekend. Took me a couple hours and it wasn't pretty. Exhaust pipe is tough to weld with the wrong machine and I'm not that skilled at welding thin pipe in and imposable to reach location.
 
its not a true stainless,,,,,sounds like the flanges are warped,,,,yes it can be welded just like any other exhaust
 
I had this same problem. Tried muffler cement and a new gasket. Worked OK for a while, but long term, it was no good. I ended up getting 2 new flanges laser cut. I braced and cut the flange off of the rear, and welded the new one on. For the front, I just butted the new flange against the old one and welded them together. Was still able to use the original studs to secure it together.
 

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