I found this site for you and it looks pretty easy and cheap to do ! Plusa quick video.
www.instructables.com/id/Zipline-Brake/
How do I install a homemade zip line brake?
I think it is an easy job to install a homemade zip line brake. I have done this successfully referring an article. You have to learn few things before doing this procedure. The important things needed for the installation are given below:
- Cable clamps
- Measuring tape
- Used tire
- Assorted drill bits
- Power drill
You will get the proper instructions from the source page given below!
Source: http://www.dimensionziplines.com/how-to-install-a-homemade-zipline-brake/