Tried changing out the driver-side cat last weekend. Soaked the bolts with PB Blaster the night before and that morning. Jacked up the driver side and removed the tire.
The aft two bolts came out with no problem (using an impact wrench). The front, bottom two nuts came off, again no problem. But that top nut....D, JD.
Had to use a series of impact extensions & swivels to be able to position the impact wrench. Had to do it by feel; you (I) can't see it. Tried and tried. Last time I pounded for over a minute...until my arm gave out trying to hold up the wrench while on my side.
Next I thought, maybe I could remove the forward bolts and twist the converter side to side to break loose the top nut.
That's when I discovered they're not just regular bolts. They're some kind of reverse-threaded Torx bolts (?). Never seen one of these. I assume if I get a Torx socket on there and crank it to the right (?) they will break loose? Maybe? Then I could go back to Plan A and try to twist the cat to loosen the top nut enough to go back in with the impact wrench.
Plan B is to find a 'friend' with a car lift and get under there with a breaker bar to see if I can get enough leverage on it. Would hate to strip the nut.
Maybe several more soakings with PB Blaster?

Anyone have any other ideas that have, or might work? Wifey wants me to take it to a mechanic, but now the thing has me mad...and I'm stubborn. I was almost there.

 

Got the Cat changed this weekend. Found a guy that has a lift.
Top nut was still the problem. Ended up getting on it with a breaker bar.
It came off about halfway and then the bolt snapped. Luckily, there was plenty of bolt left to get the nut back on.
Good thing I got it up on the lift. Changed O2 sensor forward of the Cat. No way I could've gotten to the plug if it wasn't on the lift.
Also was able to see some cracks in the tail pipe, just aft of the Cat. The guy welded over those until I can get someone to weld in a new section.

 

Was this the Y pipe or aft of that? I'm looking at welding a small spot on my Y pipe and am wondering what I'll be up against when I pull it off next month..


Glad you were able to get it done!

 

Forward of the Y. The Y splits into two pieces, just forward of it. It snakes up (almost a 90 deg left and then a 90 deg right curve) to the two forward Cats. I had the right side replaced a year ago. Should've done the left, but they didn't mention it was bad at the time.
https://i.ebayimg.com/images/g/XH4AA...Ryi/s-l640.jpg

 

Got it... Between the manifold and the Y pipe...

Thanks