Our Elantra 2.0 GLS (station wagon) developed in the last 4 months a bad exhaust leak, and became increasingly noisy. I decided to inspect the exhaust and I found the Header (Flex) pipe being the culprit.
I initially tried to patch it up with some Exhaust System Joint and Crack Sealer (made by VersaChem), but it turned out that the "flex" section itself was cracked.
The car has 93,000 miles so I decided it's time for a new cat + manifold as well, since they were relatively non-prohibitive cost wise.
I ended up ordering the parts from RockAuto.com:
--> DORMAN Part # 674551 - Combined Manifold & Converter Assembly - $ 151.89
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/Manifold-Cat.jpg)
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--> BOSAL Part # 751191 - Header (Flex) Pipe; Federal Emissions - $ 75.89
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/FlexPipe.jpg)
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--> BOSAL Part # 288011 - Resonator (Intermediary) Pipe; Federal Emissions- $ 113.79
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/Resonator.jpg)
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--> 2 x BOSAL Part # 256390 - Flange Gasket - 2 x 3.86 = $ 7.72
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--> 2 x BOSAL Part # 256398 - Flange Gasket - 2 x 2.79 = $ 5.58
The shipping was $ 32.86 for all these parts, and the total accounted for $ 387.73
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This post has been edited by WillPartHyundai: Aug 3 2009, 01:03 AM

The replacement procedure is fairly simple: take the old parts out, get the new parts in. The main hurdles are getting the old rusted flange nuts removed and also getting the PSteering Pump bracket out of the way so the manifold can slide off the studs.
I started about 2-3 days before receiving the parts to get the exhaust and the manifold nuts soaked in PBlaster.
Here are some pics with the old exhaust:
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/04.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/03.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/02.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/01.jpg)

OK, here we go:
1) Remove the cat's heat shield, three bolts:
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/05.jpg)
2) Disconnect and remove the upstream O2 sensor with a Lambda wrench
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/06.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/09---O2Wrench.jpg)
3) Now are at least two ways to tackle the next step, which is removing the Manifold + Cat. I started exactly with these two, thinking I can just drop them down and remove the whole exhaust in one piece.
It isn't a bad idea, especially if the flange nuts between the Cat and the flex pipe are extremely corroded from rust and you cannot unbolt them.
However, in retrospect I found out that probably it is better to separate the cat from the flex pipe, so that takes out any chance of nicking the manifold studs' threads from putting pressure on it. Even if cutting is involved, probabably this would be the "better" route.
a) Anyway, I started removing the manifold nuts - 9 of them.
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/07.jpg)
At this point, the manifold would not slide out unless the Power Steering Pump bracket is removed.
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/08.jpg)
In any event, the accessory belt HAS to come off (loosened up) and the PS Pump moved out of the way, with or without bracket.
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/14--PSP.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/13---PSPump-Bracket.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/15.jpg)
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Now the manifold can slide out unobstructed.
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/16.jpg)

(IMG:style_emoticons/default/cool.gif) The second way, as said, is to separate first the Cat flange from the flex pipe.
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/19.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/18.jpg)
I was LUCKY, the two nuts didn't put out too much opposition so I was able to remove them:
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/10.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/11.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/12.jpg)
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I separated the Cat from the Flex pipe (with some prying involved as the two flanges were weld together due to rust), and dropped down (yepp, in between the radiator fans and engine block) the cat + manifold with some careful angling and tks to the PS Pump being out of the way:
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/17.jpg)

4) I didn't bother with the nuts connecting the flex pipe to the resonator (intermediary) pipe as it was too rusted, and concentrated directly on the Resonator-Muffler flange.
It really took 3-4 hours to wrestle those two nuts, as they were really rusted. Actually one of them from a 3/4 profile thinned out to about 5/8.... I broke a 5/8 6-point socket which I had to tap in to get a grip. I had to go to the store and get a 12-pt socket, which I didn't have.
Finally, finally after so much wrestling (the position is also so difficult without having the car higher over your head) I was able to remove both bolts and drop the whole resonator-flex pipe assembly.
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/21.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/22.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/23.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/24.jpg)

5) Start assembly the new parts, use some anti-seize paste, and get them in the car.
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/25.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/26.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/27.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/28.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/29.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/30-FlexPipeNew.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/31.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/33.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/34.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/35.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/36.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/37.jpg)
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/38.jpg)
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And the last two nuts, by the muffler's connecting flange:
(IMG:http://i2.photobucket.com/albums/y14/PapeF/Elantra%20Exhaust%20Replacement/39.jpg)

I'm pretty sure I saved at least $ 350-400 over going to any kind of shop (indie or dealer) to replace all these 4 parts.
It is a fun project (ok, minus the headache with the stubborn rusted flange nuts), and I'm pretty sure anyone mechanically inclined should be able to do it, provided the need arises.

Good luck and enjoy (if you ever need this mini-guide).
John.

This post has been edited by WillPartHyundai: Aug 3 2009, 01:08 AM

Awesome post ! Thank you.
My flexi pipe is starting to go. I have seen on FleaBay, some standard stainless flexi sections. The idea being that you cut off the old flex pipe and then clamp the new flexi section to the old pipes. If its only the flexible part that has gone, this may be worth a try ? You just measure the Outer diameter of the old pipes and select a flexi section that will clamp round it and which is long enough. I havn't actually used this method of repair but it sound feasible. Sections of flexi are around £25.

I have seen a generic flex pipe at one of the auto parts chain stores existent on our US market (O'Reillys) for about $ 26, but it would have involved cutting and welding, indeed.
I don't possess any of this kind of equipment, so "direct fit" was the way to go for me.
Thanks.

Edit
Oh, one more thing: of course I could have only replaced the flex pipe, but the flanges on the sections were so rusted... Also I thought is about time for a new cat converter as well, but surprinsingly the old cat looks pretty clean inside (the honeycomb core), without anything loose.
Probably I'll try to sell it on Ebay.

This post has been edited by WillPartHyundai: Aug 3 2009, 11:46 AM

The flexi sections I saw were the clamp-up type so no welding needed; just two exhaust clamps and some sealing putty - like you use on the push together type of exhaust.

Also did you consider using a blow lamp on the rusted nuts? That may have helped free them but it may have needed oxy-acetaline to get enough useful heat.

I didn't want to spend + $25 on a propane torch, although I considered using heat; Maybe next time. (IMG:style_emoticons/default/smile.gif)
cheers

Just replaced my flexi pipe with a 'clamp-on' section from eBay. See:

http://cgi.ebay.co.uk/Exhaust-Flexi-Pipe-F...=item1c0d54218b

You need the 250mm X 51 that will accept a 51mm diameter pipe. Then cut the old flexi part off and clamp on the new piece using some firegum for a gas-tight seal. I found I could swing the exaust pipe back enough to slot into the new flexi section without having to remove exhaust mounts which was handy; the flexi section will compress slightly too which helps fitting. To cut the old one off I used a reciprocating saw and where that wouldn't fit, a small hacksaw.

The beauty of this solution is that you don't need to struggle undoing rusted up joints; just cut the old one off and clamp the new one on. Having said that it was a bit of a struggle making the front cut as the sump and chassis get in the way a bit but it can be done with perserverance. Also it is a lot cheaper than buying a new cat-link pipe ! (the exhaust prices here in the UK are very high on the Lantra - main dealer wants £1,000 for the complete exhaust including cat - what I paid for the car !)