Bicycle Mechanics - stuck rear derailleur barrel adjuster

I'm trying to adjust the rear derailleur on my bike and now I caN'T move the barrel adjuster at all!!The derailleur is Shimano 150 model 1050 for 6 and 7 speeds.(80s era)I took the cable out completely and that didn't help.I'm afraid to force it and hope I didn't break it completely!Any suggestions?

Drip penetrating oil on the adjuster's exposed threads and into the hole at the front of the adjuster. Give it time to work and see if that loosens it up.

sometimes you give up and put in an inline adjuster. gotta quit while you are ahead. if it is corroded a lot and has been sitting outside then i would leave it be

trek330: If the penetrating oil (I like Kroil brand best) treatment doesn't work a JUDICIOUS application of heat may help. If you do finally succeed in getting it loose, please clean it thoroughly and grease it well so it doesn't seize again. I like Tef-Gel for keeping dissimilar metals from corroding together.

I found it a lot easier to unstick an adjuster if cable and housing aren't involved. If you can't get it moving, disconnect cable and pop housing free (sometimes it corrosion between housing ferrule and the barrel adjuster that causes the sticking). One freed up, a good cleaning of all the threads, both in the derailleur body and on the screw, to remove any built up dirt and corrosion should get things moving freely again.

Well I just tried the bike with friction shifting and it seems pretty good though index seems a little rough.So the fine tuning the barrel adjuster allows isn't too crucial right now.I.ve soaked it in WD40 and I'll see if that loosens it up.I'm hesitant to take the cable out now as I'm afraid I'll mess up the adjustment I have so I'll put that off.Thanks for input and I'll report later.

Well I just tried the bike with friction shifting and it seems pretty good though index seems a little rough.
They all work well in friction mode if you have that available. In fact, rear derailleurs made before indexing was around didn't even have barrel adjusters.

They all work well in friction mode if you have that available. In fact, rear derailleurs made before indexing was around didn't even have barrel adjusters.
So for friction shifting I just have to worry about limit screws?

They all work well in friction mode if you have that available. In fact, rear derailleurs made before indexing was around didn't even have barrel adjusters.

Many derailleurs had barrel adjusters before indexing... these served to adjust the minimum cable tension rather than to dial in the indexed system.

For the OP... with a friction system the limit screws just need to be set and there should be no undue slack in the cable as you do not want the derailleur to lag.

Seized barrel adjusters can be a pita and badly seized ones can break if you apply too much force... when I service derailleurs I usually chase the threads as galvanic corrosion often occurs where the steel barrel meets the usually aluminium derailleur body.

Make sure the barrel gets well greased when it goes back together as this area is prone to getting fouled with water and dirt.

update_ got it loose!used a plier gently and it didn't break.Sticking to friction shifting anyway.