Or Stump even.
If your struggleing lifting the levers when your applieing tension then your useing too much, you should be able to feel some resistance and when the lever is set the tension wil click round a little bit.
I think ive got an old type of this lock somewhere, ill grind the top off and post you a pic so you cvan see whats inside, your lock will be very simular to it and may give you a better idea of what your doing.