That's a very common problem that many of us have experienced. The mechanism works by action of a locking shock absorber. When you lift the handle to adjust tilt, the lever presses down on a pin on top of the shock to allow it to be adjusted. After many years, rain, snow, and dirt, the pin will become gummed up. Sometimes you can disassemble and loosen the pin, but more often the shock needs replacement. The shock is a little over $100 from New Holland just for the part. I replaced mine about 3 years ago, so that's when they were $100. It's not a hard job, but has to be done correctly to make sure everything works. Were you or someone you know going to make the repair? I don't think the labor will be much so you might want to check with your dealer. Hauling the tractor to the dealer or having them come get it is going to be the most costly in my opinion.