Hello,
I recently replaced both cats on my 02 3.0 X, and realized right away that the included clamps were garbage. Sure enough, there was a significant leak (loud, smelly, can feel it puffing out) at the middle pipe and the rear cat. There were also smaller leaks but I have fixed those and had the front cat welded to its connection, as it's easy to reach from below. So far I have been to two exhaust shops and neither had any interest in dealing with the difficult location of this remaining leak. I have also tried two other types of band clamps and tightened them to their limits, copper paste, JB weld high temp epoxy and permatex exhaust putty. The permatex putty has been the most effective but cracks away after a week. Today I installed a brand new middle pipe, as I remembered seeing a slight ding in the top of the old one and had convinced myself that the divot was causing a gap. Nope, it's the exact same problem with the new pipe!

Has anyone replaced their cats and resolved a similar issue?

Is it possible to have this area welded? It is tight, but half can be accessed as shown in the photo. The other half you can reach up and grab from directly below, but I'm not familiar enough with welding techniques to know if this is too steep of an angle to work on.

Regarding the putty, I cleaned the surfaces with a wire brush and sandpaper, wiped clean. I didn't treat the surfaces with a solvent, however. Could this make all the difference? It seems the new material simply cracked, rather than failed to bond.

Thanks for any tips!


The site of the leak, seen with passenger (USA) tire removed next to CV shaft. top pipe goes to cat. This style clamp seemed the worst at first but has proven to at least get the two pipes connected tighter than the wider band-style clamps.

Collector/middle pipe as seen from below.

Types of clamps I have tried.

 

Dang, I'm sure that is frustrating after all the cost/effort of replacing the cats. I'd guess that with aftermarket cats and/or pipe the clearance of the fitting between the two is just a bit more than it should be. The exhaust putty isn't going to do much trying to apply it to the outside of the union, it will just eventually fall off. It's designed to be put on the pipes before you join them to fill up the bit of space left when you clamp them down. I'd also try a Walker Mega Clamp or similar high quality lap joint style clamp (you can find them on amazon). I'm worries that the clearance on the cat side might be a bit tight, but these cover both ends of the pipe and can work pretty well. Pull the two pipes apart, coat liberally in exhaust putty, re-assembly, coat the outside liberally in exhaust putty, and clamp down with the mega joint and I bet you'll have it fixed. There are a few bodgier products I can think of to try over the join if you get really frustrated, tiger tape or quicksteel might have a chance of working for a while, but it would still blow out at some point and it's probably worth another try at fixing properly. Good luck!!!

 

After two years of living with this, finally found a shop willing to do the welding in the tight space. $180 seemed reasonable considering multiple shops wouldn't touch it!
Chapo Mufflers in Oxnard CA