4 X 5 Graflex Series D shutter wind key very hard to turn

The shutter wind key on my 4 X 5 Graflex Series D SLR is very hard to turn beyond the 1 1/2 mark. Shutter fires fine on 1 1/2 and T settings but all other settings can only be turned with pliers which I do not want to do.
Is there something obvious that is causing this? The camera is old and has not been used in a number of years according to the person I bought it from.. I greased the curtain roller bearings, Could the the shutter roller spring be too tightly wound? Could it be a problem in the shutter wind mechanism? The research I have done indicates this unit is very hard to remove due to problems in removing the mirror rod pin.
Any suggestions would be much appreciated.

Set the tension to its lowest setting before turning the shutter wind key. Once the shutter is would to a desired aperture then set the tension to high and release the shutter, you should be able to wind back to that aperture without lowering the tension.

Thank you for reply. I tried your suggestion but was still impossible to turn. I removed the bottom plate and let the spring release and it appeared to be very tightly wound. With the spring untensioned it was very easy to wind the shutter key. I then retensioned the shutter spring with the lower tension knob at 1 and the upper shutter wind key at T. At tension 1 it was easy to wind shutter to 1/8 and the first 3 speeds completely opened and shut but the fourth speed (1 1/2) opened and closed very slowly. T only opened halfway. I moved tension to 3 and shutter wind was a bit stiffer but all speeds opened and closed properly. I moved to tension to 6 and and 1 1/2 and 3/4 were stiff but I could turn with my fingers
- however 3/8 and 1/8 would have required pliers to turn. Is there any chance that grease in the upper wind mechanism would help but I am dubious about removing the mirror rod pin?
Maybe I should keep it on tension 3 and work out what the actual speeds are. I will be using the camera with an 8 3/4 Verito and a 180mm Heliar.

Well, being you're mechanically inclined download this Graflex Shutter Servicing guide I wrote https://drive.google.com/file/d/0B1sPJkp-MdghRkRId1EwT0dpNkk/view?usp=sharing
Letting the tension spring unwind without controlling is rate can cause the spring to reverse wind and tangle.
The Super D shutter is the same as other Graflex SLR's .
The Graflex SLR instruction manual https://drive.google.com/file/d/0B1sPJkp-MdghS2llS1VaRkRIWUk/view?usp=sharing
Check out the Reflex Help section of https://www.graflex.org/helpboard/

Thanks for all your help. Shutter now working very well. Amazing that a camera of this age can still function so well. Using it with a Verito where the soft focus effect can be seen right at the time of exposure is a joy and the 4 X 5 slides or negatives can be stunning.

Happy shooting!