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Exhaust Flapper Failure - Replace with Factory or Aftermarket?

tjonesdfw
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tjonesdfw Enthusiast

tjonesdfw

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Finally had a dealer take the time to diagnose the loud metallic sound under our truck on cold starts.  They confirmed my suspicion that its something in the exhaust system and they suspect the flapper valve.  Unfortunately, the exhaust is one giant piece and the flapper is unserviceable, AND exhaust components aren't covered under the GMPP warranties.   Therefore, the repair is a $2,400 replacement of the exhaust using GM parts.  Is the Borla made GM performance exhaust the only option out there that retains a similar flapper device, ?  Trying to decide if its worth it to replace with factory exhaust or go aftermarket, and don't want any drone. 

davester Senior Enthusiast

davester

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Some people will just cut out the flapper valve, or jam/weld it open.  You might do this, just to see how it sounds.

 

And, depending on what's wrong with the valve, perhaps it could be fixed, if it's say, just the plate inside has come loose from the shaft that moves it.

 

You could advertise for a replacement valve, as some people do cut them out and likely just toss the valve.  You could buy it and have it welded in place for way less than $2400.

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Bikerjon Enthusiast

Bikerjon

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Clamp it open or have a muffler shop cut it out and install a straight pipe. I've removed 2 flapper valves on T1s and never had any drone.

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tjonesdfw Enthusiast

tjonesdfw

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32 minutes ago, Bikerjon said:

Clamp it open or have a muffler shop cut it out and install a straight pipe. I've removed 2 flapper valves on T1s and never had any drone.

I've tried clamping it open and it still rattles.  I've heard a few straight pipe videos, but they all left the flapper in ahead of the straight pipe.  Did you remove the flapper AND straight pipe on any with a 5.3? Hate to get it too loud and end up with drone as much as I drive on the highway.  Still under a GM extended warranty and know several guys who've had issues with the Range OBDII devices causing other problems.  

Bikerjon Enthusiast

Bikerjon

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On 9/3/2025 at 11:04 AM, tjonesdfw said:

I've tried clamping it open and it still rattles.  I've heard a few straight pipe videos, but they all left the flapper in ahead of the straight pipe.  Did you remove the flapper AND straight pipe on any with a 5.3? Hate to get it too loud and end up with drone as much as I drive on the highway.  Still under a GM extended warranty and know several guys who've had issues with the Range OBDII devices causing other problems.  

OK sorry if I wasn't clear in my reply. Both exhaust systems I modified were 5.3L. I did not straight pipe the entire exhaust system. I cut out the flapper valve and replaced it with a straight pipe. Then cut out the stock muffler and installed a high flow glass pack muffler. Both of these Silverados were under factory warranty. Both mods on both trucks were done at a muffler shop for under $300.00. $2400.00 for a new exhaust is crazy. I would not straight pipe the entire exhaust. My advice is take it to a good muffler/exhaust shop and have them remove the flapper valve and install a nice high flow glass pack muffler. Neither of my trucks had any drone. Lastly I have used Range Technologies DFM disable module on all my T1 trucks and never had a problem (2 5.3L and my current 6.2L).

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tjonesdfw Enthusiast

tjonesdfw

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I clamped the flapper open today and also tried the resonator screen mod.  So far it sounds ALOT better… no more rattle, clank, or chirp.  It’s a touch louder on cold start and at low speeds, but no drone or flutter yet.  We don’t have a Range device installed either.  

Boatinspector New Member

Boatinspector

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On 9/3/2025 at 8:29 AM, Bikerjon said:

Clamp it open or have a muffler shop cut it out and install a straight pipe. I've removed 2 flapper valves on T1s and never had any drone.

i took out my flapper and 2.5 exhaust pipe went with 3 inch and a 3 inch stock muffler sounds good no drone

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