Installing a 1.5-2" BB on my 01 XJ, and of course the shackle bolts were not being very cooperative. Under advisement, I soaked them down with PB blaster for a few weeks beforehand. I drilled holes on the back end of the bolt (unibody side) and soaked in PB from that end as well. Up on the jacks they went after 3 weeks of steady PB Blasting, and those bolts were not moving.
After some research, I read about a guy who took a seized seatpost out of his bike with a can of compressed air (Air duster in a can for computer cleaning). What I did was to turn the can upside down, spray the hell out of that bolt, and it was loose almost instantly on the next turn!

I suppose the principle is that the cold blast contracts the metal instantly, breaking it free of the threads. WARNING: do not let that stuff touch your skin, especially when you turn it upside down. It WILL cause immediate frostbite and bad skin damage.

Anyway, thought I would share, since as XJ people we may know a thing or two about rusted and seized threads

 

Wow. Never would have thought.

 

Nice! I never would've thought of that. I've got most of my seat belt bolts only partway out. I will be trying this very soon

 

Might have to try this out.

 

man i wish i had thought of this!

i did my shackles a few weeks ago. what a pain in the ***!! i broke both weld nuts off the frame pockets
ended up cutting the shackle bolts/ metal bushing sleaves out then took my bumper off. cut the frame ends open enough to get at the remaining bolt/nuts. then i used washers on one side to space the nut and bolt out enough to get a socket on it. i ended up welding the nut on the other side. took me 5 metal sawzal bits and 3 nights after work of messing with it

 

That is I good idea, it's similar to using heat to break free bolts. The temperature causes expansion or shrinkage in this case. I also recommend this theory for putting in bushings that are a press fit.

 

Yep. When I was installing my rebuilt ATK longblock, no matter what I did I couldn't get the pickup tube to seat all the way in the oil pump. I knew how important a tight fit and good seal was, so I didn't want to use emery cloth or anything to sand down the tube or anything.

I put the pickup tube in the freezer, and the oil pump in my oven at 200 degrees and left each one for about 10 minutes. Took them out of their respective temperature baths and they slid right together!

However, on my rear spring bolts it was lots of PB, a two foot breaker bar with another three feet of floor jack handle slipped over the end of it, and lots of grunting and cussing.

 

I tried this and I'm really impressed.

http://www.loctitefreezeandrelease.com/