I have a 940 and just replaced the pipe that goes over the rearaxle. I have tightened the clamp only moderately tight and for now there is a bit of exhaust leaking out. I don't want to go super tight until I replace the muffler too. My clamp is one I bought at Advanced Auto. Looking at it, I am wondering how it can possibly provide equal pressure as a clamp around the entire circumference of the pipes. It would seem that the pressure would not be evenly applied. Which leads to my question. Is the purpose of the clamp to deform the outermost pipe permanently in order to form a seal by mashing the metal from the outermost pipe into the metal of the innermost? Or should there be a seal that forms even without the clamp because the innermost outside diameter matches the outermost pipe's inside diameter? Also, is there a 'best' type of clamp to use instead of the cheapo one I have. One other question: what do most people use to cut off the old rusty clamps? I've given up on trying to unbolt old clamps. Thanks.

yea tightened it well

Dear Horatio,

Hope you're well. When joining a new pipe (or muffler) to an old pipe - the outer surface of which has rusted and is no longer smooth - a coating of muffler cement (gray, toothpaste-like material) will create a good seal. Apply the muffler cement to the front edge of the inner surface of the pipe, into which a component is to be inserted. The entering pipe will spread the cement.

Muffler clamps - being made of ordinary steel - rust promptly. Even if stainless nuts (or a stainless bolt and nut) are used and have been loosened or removed, the clamp cannot usually be loosened. If the clamp is "U" shaped, with a bar at the bottom, the clamp usually is corrosion welded to the pipe (or muffler). If the clamp is circular, it is hard to spread the clamp. In either case, the clamps can be cut by use of hand-held rotary tool (e.g., Dremel) with an abrasive disc. Even then, the pipes may not separate.

On a cat-back replacement, I use an abrasive diskc to make two length-wise (longitudinal) cuts in the outer pipe (the pipe that slides over the outfall pipe from the catalytic converter). The cuts in the outer pipe should not touch the inner pipe (that exits the cat converter). These cuts go about 3" towards the rear of the car. When both cuts have been made, use a flat-blade screw-driver to pry up on the metal between the two cuts. Levering gently, raise the section of metal between the two cuts, for the cuts' entire 3" length.

Then, take an ordinary hammer and tap the outer pipe (which is going to be replaced). Do NOT hammer on teh catalytic converter pipe as that can damage the ceramic honeycomb and so ruin the catalytic converter.

Tapping on the cut outer pipe usually causes the outer pipe to come free of the cat converter's outflow pipe. You can then remove the rest of exhaust system. I usually use a reciprocating saw to cut the failed units into sections.

Hope this helps.

Yours faithfully,

Spook

Yes, the exhaust clamps squash the two pipes together making it very difficult to get them apart. If the pipes are new and fit well I only tighten the clamps enough to keep the pipes from turning or leaking, whichever comes first. I don't worry about tiny exhaust leaks. I drill a small hole in the bottom of every new muffler I put on to let the condensation out. Obviously, it creates a small leak.

Either break the clamps by tightening the nuts if replacing both pipes or cut the top of the clamp with a Dremmel tool.

Greg

The best clamps are the full circle original type on Volvos--measured for size in mm. They are available from Volvo and some on-line vendors.
I use a smear of red-high temp silicone sealer on the inside of a joint--that helps seal--but also makes it much easier to make adjustments--or removal.
If you have a connection between two pipes with clamp grooves and you want to save one or both pipes you can stretch the metal by hammering directly with flat blows all the around the pipe--oxy-aceteline heat helps but isn't absolutely necessary.--Dave