Seized rear derailleur RD-M735 P-tension spring

Hey guys, longetime reader, first-time poster here.
I recently acquired a steel Giant Boulder (from around 2000) with a rigid fork, meant to be converted to a cheap winter commuter. It is in pretty decent shape, except for the fact it's a bit rusty. It needed a good clean, tune and some new cables.

Alas, I now come to the conclusion that the spring in the pivot of the rear derailleur, which rotates the cage and tensions the chain, is seized/stuck/not working. It's a Shimano XT RD-M735, so a rather classic derailleur, even considering the decade the bike was built in. Problem is there is no way (I see of) to take it apart to replace or pre-load the spring.

I added a file to clairfy what part I'm talking about. It's the spring in the red circle that doesn't do it's job. I removed the screw that stops the derailleur from unwinding (at least, that is what is should do). Also, I removed a screw (blue circle) that keeps in place a "lip" or tab. I managed to rotate the tab (it's the one in the green circle). The cage I can turn a little bit back and forth, but that's it. There is no "modern" P-screw in sight. Almost bruised my fingers in trying to pull it apart. There is no apparent way for it to release the cage.

There is little information to be found on this specific model. This link http://www.disraeligears.co.uk/Site/Shi ... ge_51.html has an image of the original catalogue. It says that it's a "sealed pivot". Now I'm puzzled: was this derailleur never meant to be taken apart? It would be a shame to just throw out a classic part like this. And now I'm almost tempted to put my angle grinder to work just to see if there is a way to release the cage.

Anyone got ideas?

Re:

hi, had a smilar Deore lx m550 apart couple of weeks ago. it looks like the pivot/cage just needs a bit of persuasion . you have undone the tab screw,the tab is press fitted to the pivot which is press fitted to the cage i would say the pivot is corroded in to the derailleur knuckle and will require pulling or tapping free. maybe try supporting it in/over a vice and carefully tapping it with a punch or try levering between the cage and mech body with a large flat screwdriver.
good luck

Re:

It's seized in, good luck getting it smooth, might need some work. It a good feeling when it works.

Prise it apart.

http://pedaldamnit.blogspot.com/2008/07 ... l.html?m=1

Thanks guys, will try ye old vice. I doubt that it will release unscathed, but the derailleur is already useless in this state, so no harm done if it fails.

If it's rusted, electrolytic cleaning is the best way to go, as it doesn't remove any of the good metal, only reconverting the bad stuff.

Re:

Thanks guys, with a lot of effort and tools I finally managed to pry it loose… but alas, the aluminum body is now cracked… It feels like a bit of a waste, but the amount of rust that came of out the body was insane; it was like someones literally drowned this bike. Replaced it with a modern derailleur so the bike now is usable again. Thanks again!

or lots of spare parts