She sat for over a year. Went to start it and clutch won't release. Have tried driving it round pulling back steering clutches and letting go with a bang, loading up by brakes on hard, up and down mounds but no release. Poured kerosene over clutch and drove it a couple of miles back to the yard but still wouldn't let go. Any ideas please.

Do you have a stuck main clutch? Is the linkage working , moving to disengaugement position ?

try chaining the blade to a tree and alternately push and then pull on the tree

I had the exact same problem with my D2 5U, tried all the easy fixes like you, ended up having to pull the clutch out, nothing was obviously wrong, but the plates were stuck for sure, luckily mine is a late model D2 and I didn't have to split the tractor.
Good luck
Mike

I wrote:

 

I don't recommend letting steer clutch levers on 9u's bang as you put it. I was told by the old timers it breaks the center shaft. I had muddy hands and had one slip away from me, and it broke the short side of the center shaft. A complete tear down of steering clutch to fix it.

And hopefully this shows up unlike the first try.

When you move clutch leaver the clutch brake moves back and forward but dosent disengage

wet or dry clutch?

RUST - stronger than SUPER GLUE!  Fills gaps as well as filler rod too.

Dry Clutch -- Assuming it may be a double disc clutch?
I would use a whole lot of thought about trying to break it loose by RELEASING STEERING CLUTCHES under POWER!
DAMAGE FROM such actions can result in Catastrophic failures - just remember, all components are only as strong as the weakest part.

I have first hand experience with "Frozen-rusted-stuck" slip clutches designed to protect drive lines and drive trains.
Category 4 shaft on John Deere HX 15 mower looked like a rifle barrel, of course the U-joint went to parts somewhere close to orbit. All due to a clutch pack that was rusted to the drive plates! I don't think the governor even had a chance to react to the instant loading on the tractor. 
Needless to say - I am not a fan of "slip clutches", I would far rather work with flanges and shear bolts, sure saves a lot of mess and expense.
In the event a slip clutch assembly does slip, it often results in total loss of the very thin linings so back to replacement again.
( When I was in the Snow Removal work - many of the snow blowers were powered with 12V71 Detroits, through a torque converter, to the drive line. 2 - 1/4" scored grade 5 bolts in the primary shear flange delivered the power to the blower head. I do not recall ever losing a drive line. The reels or augers usually had 3/8 or 5/16 bolts in the shear flange, set 180 degrees apart, the fans, also shear protected, had 2 - 3/8" bolts, same bolt at teh auger-reel. Sure saved lots of drive lines and gear boxes!)


Years ago, my father "broke" the stuck clutch plate in our Ford NAA by using a flattened file tang, carefully drove it between the flywheel and clutch disc with the Clutch Pedal in dis-engaged position. One must be gentle and try in several locations working slowly.
Do not get the "prying" instrument between the lining and the clutch disc itself, they are typically riveted and you will either pop the rivets or break the lining.
Make sure the clutch linkage is in the released positions - something has to be able to move as you "wedge" the disc from the plate or flywheel.

I should also remind everyone - RUST or corrosion fills gaps and space.   If there is no place for movement, driving a wedge in between the clutch disc and the steel pressure/plate flywheel will only result in damage.     Careful Examination is required before one damages components.

We have all seen Steering Clutch packs that have rusted so badly, the springs had to be cut off with a torch and the pack was total garbage.

Proceed with care, wear eye protection!

CTS