[Mazda]

       
Hi, The easiest way to do this is with a simple piece of bent brass rod. Some people have used a metal paper clip. The rod that I use is .81mm, I use a piece about 3” long and bend it around a small paint brush handle. I then drill two small holes in the back of the chassis being carful that you avoid fouling the crown gear. Start with a very small drill and try to get the hole so that the rod is a tight push fit. When you are happy with it secure it in place with super glue or I prefer araldite.
When the glue is completely dry sit the car on the track and carefully bend the bar down until it is close to the track but not actually touching it. I hope this helps.