How to disassemble this v brake arm? I have managed to repair 10yr old diamondback hybrid as different parts fail. I even disassembled the rear wheel to replace few spokes. But I cannot figure out how to disassemble the rear v-brake arm. (I already replaced the front.)



In the second image you can see the regular bike bolt on the left. When I unscrewed that the arm came off. But looks like the bolt doesn't directly connect to the frame and there is something else (a boss?) between the bolt and the frame and that came off with the bolt.



The new brake (Shimano Mountain Bicycle V-Brake - BR-T4000 - Rear) is exactly like the old one, but does not have this extra piece. So I need to dissamble that from the old brame arm and reuse.

So far I have tried soaking in wd-40 and also freezing the whole thing and then heating the boss(?) but neither worked.

Also noticed that this piece is tubular and has threads inside. A regular bike bolt fits in there and probably it goes all the way. So screwing something into that doesn't give me much grip either because it turns the same way.

Any ideas other than 'take it to the bike shop'? Thanks.

The reason I need to replace the brake is that the small metal rod which pushes the brake away during releaseing the brake broke.
Looks to me like you've managed to unthread the brake boss from the frame.  That's not part of the brake lever.

Normally you'd undo the dome-head silver bolt visible on the left side of your photos.

If you stick a 5mm allen key/hex tool in that bolt, and mount the allen key in a vise would be a start.  Then you need to grasp the thread and undo it without damaging the thread.... that's difficult.

One "dirty hack" is to find two nuts of the same thread and internal diameter.  Thread them on fully and cinch them up against each other as hard as you possibly can.  Then put those two nuts in your bench vise tightly, and use a long arm 5mm hex tool to lever it off.