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A4 B5 Flex Pipe / Downpipe replacement DIY (with Pics & Video!)

Old 01-09-2011, 04:24 PM
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Exclamation A4 B5 Flex Pipe / Downpipe replacement DIY (with Pics & Video!)

So your flex pipe is busted or about to get busted or whatever the case may be... here is your writeup to replace it!

Complete replacement: around 160-230$ depending one where the downpipe/flexpipe section is bought

Welded fix: 25-45$ for the flex section and another 10-20$ for the welding

Parts that should be replaced: cat to downpipe gasket and all three 13mm bolts with nuts and washer. (OPTIONAL)

The flexpipe and downpipe connecting to the rest of the exhaust.

You will be working on some TIGHT areas and on bolts that might have been on the car for the whole lifetime so rust or broken bolts might be involved!

Tools needed: assorted set of sockets and ratchets including EXTENSIONS for about 2 feet and some flexible couplings. Hex wrench set to make the job easier and some other stuff that should be in your garage.

Soak all the bolts over night or a week before with your choice of rust remover, wd-40 or whatever you swear by. There are 3 bolts connection cat to downpipe section and 2 bolts for the exhaust sleeve that connects the rest of the exhaust system.

If you have a catalytic converter your space will be even tighter so be aware.

Get your car on ramps or a lift so the front is off the ground.

disconnect the exhaust sleeve and pull it back so there is space in between the flex section and the rest of the exhaust to move around later on

over the passenger axle cv boot is an aluminum cover that is held in place with 3 hex bolts, its a 2 piece cover that is protecting the boot, you can leave that in place or remove it to gain some VALUABLE space to work on those three 13mm bolts that are holding the cat to the downpipe!

You will need an assortment of extensions like mentioned before to get those three bolts out from the cat/downpipe connection!

Remove the three 13mm bolts, washers and nuts. if they are rusted already, replace them now! So you will save yourself time once you have to dig into the whole thing again.

With the sleeve removed and the three bolts the downpipe is held to the car now by one spring loaded bolt. Once that bolt is removed the downpipe with the flex section should come out.

The original flex section is 2.25" or 54mm OD (outer diameter) and approx 4" long. Nobody in my town had one at all not to even mention the size. I paid 42$ for a 2.25" x 8 section of flexpipe and had to drive 45miles to get it.

JCWhitney has the same flexpipe sections for 25$ so either order yourself one from there or find a stock 4" section.

Now if you have a welder thats good, if not take it to a welding shop that does exhaust work.

I spend 20$ to have them cut of the old flex section and weld in the new one. Make sure that they use the old alignment of the flexpipe to weld the new one in as there is a bend in the lower section. It wont fit correctly if the flex section is not welded in correctly.

If you replace your stock short flex section with a longer one you need to cut off the appropriate length of that new longer section from the rest of the stock exhaust pipe.

Put everything back together and enjoy a quieter car!

Now: Some people might mention that there is no need to remove the downpipe at all from the car and that everything can be done with a lift and the right tools. Well, there is not much space between the flex section and the underbody of the car so the weld might not be as good as they could be. I'd rather have some good welds and a job well done!

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Old 01-09-2011, 05:11 PM
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Default A4 B5 Flex Pipe / Downpipe replacement DIY (VIDEO Version!)

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