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I've got a failed flex pipe on my Taurus, and I'm having some trouble removing it for repair.

The flex pipe is part of the rear catalytic converter assembly, and it's held on by two bolts at the exhaust flange on the upstream side, a hanger bolt at the rear cat, and a u-bolt onto the downstream exhaust pipe. I figured I'd have some pretty corroded exhaust flange bolts and was prepared to cut them out with a dremel or hack-saw, but when I got down there and hit it with a wire brush, things started looking a bit different than I expected. Rather than having bolts like these at Rockauto, it looks like there's a stud on the downstream side of the flange, and a nut on the upstream side. It looks like they're welded on to both sides and there's no thread on the bolt side, making removal a lot more difficult. Replacement parts on RockAuto just have holes for the bolts to go through (front, rear).

Looking towards the rear:Looking towards the rear

Looking towards the front:Looking towards the front

From below:From below

What are my options here? Chop the bolt and drill it out? Am I mis-reading what's happened here and the bolts are just really heavily corroded?

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  • The stud is welded, the nut is severely corroded, soak it with you favorite rust dissolver for a day or two (without driving) before attempting to remove.
    – Moab
    Jul 15, 2019 at 15:44
  • Stud is welded in an attempt to prevent catalytic convertor theft. The metals inside are quite valuable to theives.
    – Old_Fossil
    Jun 8, 2020 at 8:53

3 Answers 3

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I think you have just polished up the rust on those nuts and bolts with the wire brush. I am pretty sure if you gently repeatedly tap them with a hammer, the rust will fall off. Since they will be near the CAT, it is probably not a good idea to hit them hard, so just cut the old bolts off and replace them.

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It certainly looks like a weld ( first picture). Stainless does not corrode ( significantly ) in an exhaust system. I suggest some kind of grinding to remove the fasteners. Most modern exhaust pipe is ferritic ( magnetic) stainless , not very hard because of very low carbon . But, the fasteners and weld filler metal may be something else , even austenitic ( non-magnetic ) stainless . Austenitics are soft but work harden very fast so are difficult to drill.

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  • That's a shame. I was hoping to use the existing flanges and weld a new flex pipe in. Depending on how much material I have to remove, that may not be an option.
    – Jason_L_Bens
    Jul 15, 2019 at 1:24
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    It looks like you should be able to get an angle grinder's cutting wheel on those and slice them off parallel to the flange @Jason_L_Bens. You might be able to hammer out the bolt if you're lucky, if not drill it out.
    – GdD
    Jul 15, 2019 at 13:09
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A late answer but it might help someone else: Everything seems to be design engineered for easy assembly at the auto plants. The converter arrives at the plant with studs attached and tack welded, so that it survived that journey. The stud is splined where it goes into the converter so it doesn't spin and would be a one hand install at the plant. For you that means you need it cut the head of the stud off, or at least cut the tack weld. Then drive the stud out. (it won't turn, it's splined.) Then just drill out the hole to remove the splines and use a regular nut and bolt, preferabbly stainless.

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