I've broken my 1/2" breaker bar and my 3/4 to 1/2" extension while using my 3/4" breaker bar trying to get the axle nut off.

What, is it welded on??

 

Probably not. You may need to get a torch and heat it as long as you won't cook bearings or something.

 

Buying your tools at harbor freight by chance? Got pictures of the busted tools?

Like rspi said, heat may help. How about a 1/2" CP pneumatic impact wrench?
This should do it..
Chicago Pneumatic - CP734H - 1/2

 

I just replaced both, had to use a long tube extension for leverage.
A bit of PB blaster helps
I did not need the torch, but.. That helps..

 

Got the 1/2" breaker bar at NAPA, 3/4 to 1/2 adapter at Advance Auto.
I don't think the air wrench will help. Already have one and I'm using a 4' cast iron pipe as an extension of the breaker bar. I'm not going to get more torque than that out of a 1/2" impact wrench. Yesterday, took it down to a mechanic to ask if he could use his 3/4" impact wrench to get it off. He says the 3/4" breaker bar with a good extension puts alot more torque on the nut than the impact wrench. He also said that volvo sometimes uses permanent locktite on those axle threads--probably to keep people from doing their own repairs. Said heating it up should do it, so I'm gonna give that a shot today. If I break another extension, then I'm gonna order a 3/4" drive 36mil impact socket to use with my 3/4 breaker bar.
...either that or maybe I'll try cutting the nut off with a grinder.

 

Heated it up and still broke the adapter. I guess I'll try to source a 3/4" drive socket.

 

I usually heat it until it's almost red.

 

If I get it that hot, wont it damage the bearings?

 

Probably, so... don't do that. Goes back to my 1st post here. Make sure you heat that sucker up pretty good. Why are you taking it off in the 1st place?

 

I'm changing the axles, tie rod ends and control arms.
I ordered a 3/4" drive 36mm impact socket from napa, so I'll try heating it again and using the 3/4 breaker without an adapter when it comes in tomorrow.

Any other suggestions?

 

No, if you know any real heavy people that might help. I have had to get my nephew to help me break a few things loose. He's 525 lbs.

 

3/4" breaker bar, 3/4" 36mm impact socket, 4' cast iron pipe as an extension.

Took care of both the axles nuts with no problem. I guess that's the winning combination.