Downpipes to 'resonator' nuts?

[Pinger]

Another 'what size are my nuts?' thread.
Exhaust replacement beckons but not until next week when it arrives. Truck is 1999 C2500 Suburban 5.7l and has dual cats that then join to twin pipes (resonator?) which lead to a single muffler (dual inlets, single outlet) which I believe is what it would have left the factory with.
The connection between the cats and twin pipe (resonator?) is secured with three nuts. What size are they? They will likely need replacing and if metric I probably have lying around but not so if imperial - they'll need to be ordered. Metric or imperial and what size?
TIA.

 

[xXxPARAGONxXx]

Highly likely M10 x 1.5 flange nuts.

 

[Schurkey]

1. I wouldn't expect a resonator. More likely two plain ol' exhaust pipes leading to a hugely-restrictive muffler.

2. If this flange is made like I think it is, the bolts and nuts are easily replaced--and should be, 'cause you'll probably break 'em trying to get them apart. I have a flange like that between the two catalysts on my '97 K2500 7.4L. Flange is easily warped, doesn't seal at the gasket worth a crap. Total pain in the tuckus.

Uses this gasket:
www.oreillyauto.com/detail/c/nickson/nickson-muffler-gasket/nic0/31618/v/a/3428/automotive-truck-1997-chevrolet-k2500-pickup-4wd?q=Exhaust+gasket&pos=2

https://www.oreillyauto.com/detail/c/nickson/nickson-muffler-gasket/nic0/31618/v/a/3428/automotive-truck-1997-chevrolet-k2500-pickup-4wd?q=Exhaust+gasket&pos=2

 

[Pinger]

1. I wouldn't expect a resonator. More likely two plain ol' exhaust pipes

Resonator is the term Rock Auto use for what I see as twin pipes, which, judging by the gasket are of different diameters - why?

2. If this flange is made like I think it is, the bolts and nuts are easily replaced

I forgot to check or ask if they are bolts or studs. I assumed studs hence the question about nuts but if bolts then new ones will be used.

--and should be, 'cause you'll probably break 'em trying to get them apart.

Exactly what I'm expecting.

I have a flange like that between the two catalysts on my '97 K2500 7.4L. Flange is easily warped, doesn't seal at the gasket worth a crap. Total pain in the tuckus.

Uses this gasket:
www.oreillyauto.com/detail/c/nickson/nickson-muffler-gasket/nic0/31618/v/a/3428/automotive-truck-1997-chevrolet-k2500-pickup-4wd?q=Exhaust+gasket&pos=2

https://www.oreillyauto.com/detail/c/nickson/nickson-muffler-gasket/nic0/31618/v/a/3428/automotive-truck-1997-chevrolet-k2500-pickup-4wd?q=Exhaust+gasket&pos=2

I'll keep those gaskets in mind if I have sealing difficulties. Time and geography are against me for now.

Re restrictive muffler. It may well be but when you see (I'll post photos) of what will be removed - a lash-up with umpteen welds that cannot be other than restrictive - I doubt I'll be worse off.

 

[HotWheelsBurban]

Resonator is the term Rock Auto use for what I see as twin pipes, which, judging by the gasket are of different diameters - why?


I forgot to check or ask if they are bolts or studs. I assumed studs hence the question about nuts but if bolts then new ones will be used.

Exactly what I'm expecting.

I'll keep those gaskets in mind if I have sealing difficulties. Time and geography are against me for now.

Re restrictive muffler. It may well be but when you see (I'll post photos) of what will be removed - a lash-up with umpteen welds that cannot be other than restrictive - I doubt I'll be worse off.

That must be the standard Suburban exhaust; it's what my Burb has. The converters are made into the head pipes coming from the exhaust manifolds, and the back end has that 3 bolt flange you're talking about. We had to replace the cats on the other '99 Burb and it was not fun at all. The stock muffler is huge, and is a 2 in/1 out setup. Probably room for a pair of smaller mufflers like Corvair type turbos or glasspacks, but then you'll need two tailpipes (one reason I haven't done it!). The crew cab has true dual exhaust, parallel pipes rearward of the cats. The paired tailpipes are cut off just past the rear axle (by PO, presumably to keep from catching them or damaging them in a ditch?).

 

[Pinger]

That must be the standard Suburban exhaust; it's what my Burb has. The converters are made into the head pipes coming from the exhaust manifolds, and the back end has that 3 bolt flange you're talking about. We had to replace the cats on the other '99 Burb and it was not fun at all. The stock muffler is huge, and is a 2 in/1 out setup.

I ordered it from Rock Auto (the last one - there's none listed today) and guessed I'd be reverting to stock.

Probably room for a pair of smaller mufflers like Corvair type turbos or glasspacks, but then you'll need two tailpipes (one reason I haven't done it!).

Reverting because it is currently true dual. One pipe goes rearwards to the passenger side and the other arches across the axle to exit on the driver side. It is it that one that is rotten. I did see replacements for those but the company selling them don't ship to the UK. That, and the section between the cats and the over axle pipes is pretty doggy. Bad enough that attaching new over axle pipes would be difficult at best.

The crew cab has true dual exhaust, parallel pipes rearward of the cats. The paired tailpipes are cut off just past the rear axle (by PO, presumably to keep from catching them or damaging them in a ditch?).

I considered terminating mine forward of the axle! But, even if regulations don't forbid termination of pipes beneath a passenger compartment (not a problem with pick-ups) the tail pipes have to be accessible for (annual) emissions testing.

 

[HotWheelsBurban]

Those regs are the same here in Texas. Our state government is doing away with the annual state safety inspection as of next year. Though vehicles that are new enough, in counties that still require emissions testing and inspection, will still be subject to that. Rawhide is already old enough to be exempt from emissions testing and inspection, and Burb will be at the first of next year.
The officials who pushed that bill through, say that they're freeing up Texans from having to "spend all day to get their car inspected".... The place I used to go never took that long, an hour or so usually. And now I don't have to mess with it at all.

 

[GoToGuy]

You always go to " GM parts giant.com " . Enter your VIN it will take to parts category for your year model . Then choose what section, steering , drivetrain , body, exhaust. Then scroll through the listed parts,. Tip: it will give you the GM part number, and AC Delco number if carried by them. Also if a type of hardware the description will size it; 1/4 x 20, 4 inch stud, or 6mm x 12, 100mm bolt. Drain plug 1/2 npt with gasket.
GM and ACDelco part numbers can be sourced from multiple vendors, not just GM.
The parts may be available from GM, but the number can still be good on the after parts market.
A Lot of GM hardware, that I'm not sure about I'll use the Full parts sites, listing all parts including the no longer available parts; not the abbreviated websites that don't list all parts.
Why guess or wait for responses that may never show, or close but quite correct.
Good luck!

 

[Supercharged111]

15mm wrench on the nuts, so the aforementioned 10x1.50mm. If you snap one off though, don't just try beating it out. It'll bend the flange.

 

[Orpedcrow]

You always go to " GM parts giant.com " . Enter your VIN it will take to parts category for your year model .

This is an awesome tip.