Seth,

I am replacing my cat on a 1990 240 (California model) and had a lot of trouble regarding the cat to down pipe joint.

You are right, you don't have to worry about the fixed or swivel flange, but the problem is what type of gasket that goes between the cat and down pipe.

My guess is that you have one of those seal ring gaskets, not a flat aluminum ones. These type of gasket needs a open flare to work.

So my recommendation is that you take the cat off, and see what type of gasket you have. If you do have a seal ring gasket (imagine a small donut like device), then put the unit back on and order one from FCPgroton ($129 bucks). (I assume your unit is fairly rust free and simple to take off)

FCPGroton is the only place that sells the correct cat. I ordered one from them last week.

Unless you put the wrong header on six months ago, I cannot imagine why you would need a new one now?? That is one part that almost never needs to be replaced. Are you dealing with Midas or a place like that? If so, go where they speak Volvo.

I think that if you are replacing the exhaust system all the way back I think you would be perfectly fine using the original header pipe and getting a replacement cat. I can't think of any reasons why that wouldn't work. Look on the bright side at least you don't have to buy a $500 cat like on the turbo models :)

Charles 1985 245ti with exhaust leak at cat :( and bad head gasket???:(

I put a cat (aftermarket) on my '86 245 last year and a new exhaust pipe this spring. Everything fit as original.

The aftermarket cat mated perfectly to the Volvo pipe (flange, three bolts), and to the front muffler (pipe fitting).

The new pipe was identical to the old pipe and fit perfectly.

Who told you that you need a different pipe?

You can probably buy a very suitable replacement pipe that will mate to the pipe from a decent auto parts store. Check the on-line folks, such as FCP Groton.

Use the metal-clad Volvo gaskets, though.
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Don Foster (near Cape Cod, MA)