Collar tilt patio umbrella ALWAYS tilts when umbrella is fully open.

I'm looking for a way to permanently disable the tilt feature on my collar tilt umbrella. (Casual Cushion Corp is the brand through Improvements Catalog - about 5 years old). I've taken it apart and can't figure out how the tilt mechanism works. The crank, rope, and pulley are just fine, but the collar is just plastic and I'm pretty sure it's been over tightened during use (clockwise tilts and counterclockwise straightens) so the inside plastic looks stripped out. Again, just want a way to still be able to raise and lower the umbrella without tilting. Thanks!