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Old 06-18-2016, 08:33 PM   #1
xdarkxfirex
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Default Replacing flex pipe

I need to get mine done. It isnt leaking but IDK if it was pass inspection. It looks like it was previously welded, not very well, and the metal strands are falling apart. I bought a walker one, but I dont think its the right size. What is the right size diameter, and length?

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Old 06-18-2016, 10:02 PM   #2
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Default Re: Replacing flex pipe

Year, model? I'm not sure what your state DMV requirements are as they may require sealed exhaust systems (welded) or at least correctly fitted replacement parts that are leak free. My guess is as long as the emissions system doesn't generate an error code related to the exhaust system, any repair can be either welded (preferred) or bolt on. I replaced one of two flex pipes on my L300 without welding, using a sawzall to cut out the damaged flex pipe and bolting in a stainless replacement. I shopped extensively online (Summit, other sites) to find a replacement and found two types, one made for welding with no ends and bolt on with ends. I made measurements to my exhaust pipe and went to Autozone (the only store stocking flex pipes, adapters, etc.) to see exactly what I needed as inside and outside diameters vary a great deal. Never having experience in exhaust systems, I studied every possibility of doing it wrong before figuring out what fit. My flex pipe was 3 inches long from weld to weld and was missing the rings that covers the stainless braid ends (rusted off). I suspect that's what you're describing, the stainless braid with the end rings missing from corrosion. The stainless braid is a cosmetic cover to the actual corrugated pipe that flexes and cracks from normal wear and tear. Place your (gloved) hand to feel for exhaust pressure leaks and noise on a cold engine before the pipes heat up. A crack in the flex pipe will blow thru stainless braid. A bolt on flex pipe is the easier repair unless you want it welded to the existing system (presuming no severe corrosion). I am by no means an expert on exhaust system repairs but here's my experience; http://www.saturnfans.com/forums/sho...d.php?t=219074

Measure the outside diameter of the exhaust pipe right at the flex pipe location to have a base dimension. The replacement flex pipe will either be a slip fit or need a pipe expander tool (free loaner from A-z). Although I borrowed the pipe expander, I didn't' need it and presume the flex pipe ends are expanded to fit over the exhaust pipe in cases where dimensions are wrong. Google pipe expander for an idea of what it does.

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Old 06-18-2016, 10:19 PM   #3
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Default Re: Replacing flex pipe

I may consider welding them on myself but I have a flux core which is not good for stainless steel. I replaced the muffler with the original, since the aftermarket was loud. I think the flex pipe is throwing the p0420 code. Wanna get it fixed, and I'm gonna replace brakes all around to pass safety. I already passed emission. We need no leaks here too

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Old 06-18-2016, 11:18 PM   #4
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Default Re: Replacing flex pipe

I have a lot of spare time to watch all the youtube videos on mig/tig welding for education. I'll probably never use it but was always interested. I've tried sputter welds on conveyor belt covers and made some high amp welds on heavy gauge steel (not for structural support). My guess; the rings covering the ends of the stainless braided cover was an afterthought (tack welded?) that simply rusts and falls off compared to the welded flex pipe to the exhaust pipe (low grade stainless?). I realize how important it is to select the right compatible metal for welding stainless (among the hundreds of details needed to weld correctly) to prevent poor welds, setting up future corrosion from using the wrong filler (all youtube info without digging up a welding book and getting lost in it), etc... Pros show how well welds look against most amateur welds like mine.

You're the only one in position to know if welding will work on existing pipes and if its stainless or not. A leak is only one of the possibilities to P0420.

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Old 06-19-2016, 10:23 AM   #5
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Default Re: Replacing flex pipe

These are the two flex pipe posts I found helpful when I had this problem

http://www.saturnfans.com/forums/sho...d.php?t=190789

http://www.saturnfans.com/forums/sho...ight=flex+pipe

A local independent guy replaced mine in 30 minutes and it was relatively cheap. These are high-fail parts so if you are getting exhaust components off an 8 year old Astra in a junk yard, consider replacing the flexpipe before installing...

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Old 06-19-2016, 04:27 PM   #6
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Default Re: Replacing flex pipe

Here are two examples of flex pipe configuration.
Attached Images
File Type: jpg flex pipe-1.jpg (28.3 KB, 14 views)
File Type: jpg flex pipe-2.jpg (61.2 KB, 11 views)

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Old 06-19-2016, 05:27 PM   #7
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Default Re: Replacing flex pipe

I tack welded mine since I couldn't get that piece of the exhaust off the weld, used muffler cement and bolts. I can hear a leak from the system and the bolts don't have much material to hold onto. The back is fairly loose
Attached Images
File Type: jpg IMG_20160619_125105637_HDR.jpg (95.0 KB, 17 views)

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Old 06-19-2016, 06:23 PM   #8
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Default Re: Replacing flex pipe

Is this flex pipe the one with extended ends slipping over the exhaust pipes? If so and muffler cement was liberally used to help with sealing against exhaust leaks, the clamps should be placed about midway on each extension to allow full clamping with cement sealing from both sides of each clamp. While not pretty, as long as the clamps fit on a straight portion of pipe, rechecking this over the next few days with a wrench test can help tighten loose fittings to ensure against leaks. Wrench check clamps with a cold engine, start up and feel for exhaust leaks to prevent burning a hand or fingers and make another wrench test on clamps. In theory, when everything settles with a few engine heat cycles, this repair should last forever until the exhaust system rusts apart or the catcon disintegrates. Clamps mechanically hold ends together but cannot prevent flexing where the rest of the exhaust system is hung from original hangers. Some flex pipe repairs needs welding more than others as each flex pipe is custom designed from the factory to minimize noise transmitted into the chassis while still allowing engine movement without damaging exhaust systems using flex pipes in designated areas.

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Old 06-19-2016, 07:38 PM   #9
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Default Re: Replacing flex pipe

Interesting that the flex-pipe should be associated with transmitted noise into the chassis. My exhaust is a patch work quilt, and I have this annoying drone that comes on at 2700 rpm. Just assumed it was mount problems. The exhaust as a whole does rattle once in awhile taking off in 1st. Does anyone know the actual flex section's length, mine seems to be a real stub about 2" long.

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Old 06-19-2016, 08:49 PM   #10
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Default Re: Replacing flex pipe

Its much louder with the leak. I'm not even gonna bother trying to fix it myself. My neighbour has a shop and does it very cheap. I'm just wondering if he can reuse the pipe with the the cement on the side. I could've gotten away with clamps, but there wasnt enough room to fit them onto. The place I bought it from, A&A only cost me $15 total. I heard clamps dont work too well, but I dont know. Maybe some loctite will help them against become loose.

I'm interested in knowing if walker, and any aftermarket companies make the exhaust system for the astra. I broke a manifold bolt trying to get the pipe off from rust, but no leak from there. Will probably get it replaced tommorow. Its a hard task welding under a car with a few inches of clearance, and wire flying over your face.

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Old 06-20-2016, 12:31 PM   #11
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Default Re: Replacing flex pipe

Loctite is useless in this application. Exhaust heat melts Loctite. Welding or mechanically clamping exhaust systems are two solutions but considerations are needed where welding is better than clamping parts. From descriptions and pics from other members about the layout of this flex pipe in relation to the rest of the pipe determines whether or not clamping a replacement flex pipe will work. Consideration must be made to see if a clamped flex pipe will hold up to normal engine movement in its motor mounts without straining the clamps holding the flex pipe to the two pipes. Another consideration is whether or not motor mounts are worn or broken. The suggestion to use clamps over welds is not an easy choice when examining the exhaust system. Welds are done for a reason; structural integrity, long life, less parts, less corrosion compared to clamped parts where areas are more likely to wear out and replacement is easier.

The cement is easy to break if redoing this repair. If welding is needed, grinding or sanding down to bright metal allows welding clean parts together.

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Old 06-20-2016, 12:48 PM   #12
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Default Re: Replacing flex pipe

The mechanic fixed the broken flange stud, cleaned off the cement and rewelded. He charged me $50, which is still a good price, didnt need to buy another pipe. While the car was up, I noticed my sway bar links are going.

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Old 06-20-2016, 12:48 PM   #13
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Default Re: Replacing flex pipe

Dryer always has great insight!

My buddy (who only does exhaust systems) replaced my flex pipe in about 20 minutes. Other machine shop friends have had him do muffler repairs and said his work is superb.

His daughter has an Astra ironically so he had done this flexpipe repair before a few times.

I peeked in the workshop while he was working on the Astra for a few minutes and their technique to weld was to raise the car on a lift, remove the exhaust from the hangars and by angling the exhaust down towards the floor that gave them plenty of clearance for a good weld.

I had a few GTIs in the past and the clamping/puttying downstream components just never sealed very well. I assumed that was due to bad technique and high pressure from the 100bhp engine!

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Old 06-20-2016, 12:49 PM   #14
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Default Re: Replacing flex pipe

Quote:
Originally Posted by xdarkxfirex View Post
The mechanic fixed the broken flange stud, cleaned off the cement and rewelded. He charged me $50, which is still a good price, didnt need to buy another pipe. While the car was up, I noticed my sway bar links are going.
$50 is a great deal, especially for clean up work which is somewhat painful!

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Old 06-20-2016, 02:06 PM   #15
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Default Re: Replacing flex pipe

Before I needed an e-test, I knew my flex pipe was going out a second time and I needed to install new O2 sensor after, all with the want of a little more noise from the exhaust. I ended up getting a full custom magnaflow exhaust built for my car from the first cat back. Removed the secondary cat.








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Old 06-20-2016, 02:13 PM   #16
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Default Re: Replacing flex pipe

Not the best quality video but seems the sound didn't get down graded


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Old 06-22-2016, 10:36 PM   #17
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Default Re: Replacing flex pipe

I bought a 2" flex pipe from a local auto parts store for $15, paid $50 to get it properly welded. Sometimes having a lift makes the job much easier. What I learned. Never try to weld again without a good angle, and that muffler cement is garbage. A few wacks, and its all gone. Made my car sound like a ricer civic. I used a scrap OEM muffler. Much less noise. While I had my muffler damaged, I had a too lean code, then low cat efficency code. Havent had any codes since I got the flex pipe fixed.

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