Exhaust gasket keeps failing

[Joe Bltsphlk]

1999 suburban, 5.7, 140K miles. The exhaust gasket between the cats and the muffler (Y-pipe connection to intermediate pipe) keeps failing. I have tried various brands, from Dynomax to Walker. It is part #31575 and has the two holes.

History: The first time I replaced the gasket, I twisted off the studs so I replaced them with SS bolts and use never-seize to make it easy to remove next time.

The cats were replaced a year ago with a new Walker 50410 because the passenger side pipe near the manifold kept cracking and weld repaired, but eventually split open all the way to the O2 sensor 1.

A shop advised me to try using some Permatex 80335 Muffler and Tailpipe Sealer on the new gasket. I tried this and it still failed after a few months.

In my latest attempt, I stacked two gaskets and liberally applied the Permatex on all sides of both gaskets. This has survived for 6 months, but is now leaking again.

What are your suggestions? I'm starting to wonder if I have a restriction in the muffler that's causing a higher than normal pressure inside the exhaust system.

[j cAT]

Originally Posted by Joe Bltsphlk

1999 suburban, 5.7, 140K miles. The exhaust gasket between the cats and the muffler (Y-pipe connection to intermediate pipe) keeps failing. I have tried various brands, from Dynomax to Walker. It is part #31575 and has the two holes.

History: The first time I replaced the gasket, I twisted off the studs so I replaced them with SS bolts and use never-seize to make it easy to remove next time.

The cats were replaced a year ago with a new Walker 50410 because the passenger side pipe near the manifold kept cracking and weld repaired, but eventually split open all the way to the O2 sensor 1.

A shop advised me to try using some Permatex 80335 Muffler and Tailpipe Sealer on the new gasket. I tried this and it still failed after a few months.

In my latest attempt, I stacked two gaskets and liberally applied the Permatex on all sides of both gaskets. This has survived for 6 months, but is now leaking again.

What are your suggestions? I'm starting to wonder if I have a restriction in the muffler that's causing a higher than normal pressure inside the exhaust system.

I would use a pipe frame support at the y pipe connection. with pipe movements this will happen .then you get into bad engine/tranny mounts or even bad exhaust hangers on the rear . I would not use any anti seize on the SS bolts/nuts they will loosen. I would also use a double nut to lock these in place so they will not loosen. or use a self locking SS nut .