Goodday friends neighbors and automotive enthusiasts. I am in the possession of one 1992 Mazda Miata that has lived a relatively comfortable life during its 105k miles garaged every winter and relatively well maintained before it came into my possession. There have been some minor convenience issues like converting the A/C to R134. https://www.instructables.com/id/Adventures-in-Auto... and replacing the radiator and all the hoses.

To pass a safety inspection in MO a vehicle is required to have no leaks in the exhaust system. Unfortunately for me one of the heat shield clamps held on to moisture and rotted a crack that was dumping CO into the passenger compartment.

To get around the annoyance of a leaky exhaust for a little while I used some of the fiberglass repair tape over a tin can. Needless to say that bandaid fix lasted about 3 weeks before I had my leak back. put off replacing the whole exhaust and breaking 23 yr old rusted bolts I decided to just cut out the rotted section of mid pipe and replace it with a section of exhaust pipe and two u bolt muffler clamps. Please follow all local regulations and laws.

The section of exhaust pipe that I am repairing in this Instructable, was where a 2 inch wide clamp held on the heat shield to prevent rattling. Over time water worked its way between the metal pieces and the galvanic properties of dissimilar metals rotted it away leaving a narrow strip of metal holding the midpipe to the muffler. To my delight the rest of the exhaust pipe appears to be good and tapping it with a ball peen hammer did not cause any other sections to fail. Had it broke elsewhere I would have just replaced it from the catalytic converter to the muffler tip. This fix involves about $10 in parts. Actual mileage may vary for your application.

Parts required for this fix your diameters may be different.

1-2" x 2" exhaust adapter pipe . $3 (Slightly bigger then the 1 7/8 Exhaust pipe but I will expand on that later pun intended.)
2- 2" muffler U clamps $3 each
11 3" hose clamp (to secure the heatshield to the new pipe)

Tools Used

Reciprocating saw with Metal cutting blade
4 1/2" grinder
Socket set
Breaker Bar
Small Prybar (yeah I used a screwdriver as a pry bar outside the recommendation on the tool)
Medium exhaust pipe expander.
Safety Glasses.
Hearing Protection.
Automotive Jack
Jack stands
Lug Wrench.
Wood Block
Rope...

Step 1: Block and Jack the Vehicle.

The first step will be to safely jack the vehicle and in the case of my car remove the drivers side rear wheel for access to the rotten section of pipe.

Set the emergency brake of the vehicle
Set the transmission in park or 1st gear.
Wedge a block under the front edge of the tire opposite the end of the car you are working on.
Set Jack at manufacturers lift point
Jack end of vehicle
Place jack stand in manufacturer lift point.
Use lug wrench and remove any hub/center caps
Remove lugnuts
Remove wheel from vehicle.

Step 2: Cut It Out.

As I tried a bandaid fix to get by, however after a couple weeks it failed and was allowing nice CO to creep into the passenger compartment again. Good thing this is a convertible and as airtight as a colander or I would have been in trouble.

The first thing to do here is to remove the muffler bandage with a pair of wire cutters and a pocket knife.
Now that the rotten section is exposed I used my reciprocating saw to finish the crack that the rust started. This will also separate the heatshield in twain.
Using a screwdriver as a prybar (not recommended) I gently pried the rubber hangers from my muffler and worked the muffler around the rear axle and out from under the vehicle.

Step 3: Make It Right Round Baby...

right round, like a muffler baby, right round, round round...

The rope came in handy as an improvised 3rd hand to hold the muffler to the bench while I cranked on it with a breaker bar. The section of mid pipe was placed in the jaws of my vise and the rope chain was looped around the top of the table then through the bight that I hang it from with the excess looped on a muffler hanger I didn't need it clamped fast, but I did need it to not move as much.

Ok now that I have the muffler from out from underneath the car lets see how bad it really is. Ok it is about as round as a jelly bean that is going to have to get resolved.

I broke out the grinder with a 40 grit metal disk and ground away the rust from the cut.
keep removing material until the pipe is of a uniform thickness.
Next I blew rust from the tailpipe using a can of compressed air and gave the pipe expander a generous coating of oil.
I got frustrated with the heatshield and bent it out of the way. It was really the only way to inspect the pipe underneath.
Insert the pipe expander into the tail pipe and use a breaker bar to get it back into round. This required a bit of tweaking to get it just right and after a while I had it mostly round but needed to tap it with a hammer to get it the rest of the way using the expander as a form. Make sure you go slow and test fit the coupler to ensure that the pipe is not expanded too much.
Although I don't have any pictures of the underneath of the car i used pretty much the same process to get it to fit my coupling snugly.

Step 4: Put It Back Together.

Well that sounds easy right? In theory it is but if you noticed from the beginning of the process to the end I lost my daylight. So I apologise about the dim pictures. It is surprisingly tough to get a decent picture while on one's back under a car holding a tool and trying to show how one is trying to do something.

Slide the end of the coupler over the tail pipe (I used the no sticker end for my muffler side Sticker = Stick on Car side)
Slide the U bolt around the joint from the top side and fasten the other half of the clamp on the bottom side securing with the enclosed flange nuts. (I used my electric impact driver as it torques to 98 lb/ft)
Bend the heat shield back into place.
Fish the mid pipe back around the rear axle and line up the coupling with the pipe still on the car.
Maneuver the muffler back into position and reattach the muffler hangers.
Insert the exhaust pipe into the coupler and fasten the other U bolt clamp around the joint but under the heat shield.
After torquing the nuts down with an impact I started my engine and looked listen and felt for any leaks. I could not detect any however the heat shield rattling was driving me nuts.
I dug around my tool box and found a 3 inch hose clamp. After aligning the heat shield sides over each other I fastened it so that it would hold both ends in place to the new section of pipe.
Put the wheel back on
Lower the car
Clean up your mess.
Test drive.

Ahhh that sounds so much better no more BRRRRPPPPPPP from a leaky exhaust. While this fix was shown on a miata it the principals are pretty much the same for any vehicle. Just size it appropriately for your car/truck. If it is in a bend get a replacement section of bent pipe. I have also done similar repairs to replace the flex coupling on other vehicles. I hope this helps and for not much more effort then a speedy bandaid fix one can permanently fix the problem.