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Topic: 2007 Seneca Duramax: Downpipe to Cat pipe joint repair (Read 84 times) previous topic - next topic
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2007 Seneca Duramax: Downpipe to Cat pipe joint repair

I have a 2007 Seneca on a 2006 C5500 chassis with a LBZ Duramax. I noticed exhaust smell in the cabin and traced it down to the joint between the turbo downpipe and catalytic converter exhaust pipe:
X   X

OEM replacement parts listed for about $500 before shipping  :o
Here's what I did -
Parts purchased:
Walker 41646 flared exhaust pipe ($20 on Amazon)
Squirrelly 3" x 4" stainless flex exhaust pipe ($23 on Amazon)
Grand Rock v-band clamp GRVB-384G ($26 including shipping from
Felpro 61287 catalytic converter gasket ($8 at NAPA)

Cut 1.75" off Walker piece:

Cut 5.5" off cracked end of exhaust pipe:

Weld-r-up and test fit to downpipe:
X   X

Reinstall and check clearance:
X   X

So, for about $75 in parts and a little of my time, I'm hoping the flex joint with relieve the stress and keep it from cracking. I should be no worse off than if I had implemented the oem parts except that I have extra money in my pocket for other things. I hope this helps someone else like this site has helped me! Your mileage may vary...


Re: 2007 Seneca Duramax: Downpipe to Cat pipe joint repair

Reply #1
I have a brand new item 3 in the drawing. I have no need for it.
Your fix looks good.