I'm performing parkour for about an year and a half now, and when i was beginning, i had the same problems.
here are some eazy tips:
-Overcoming the fear: keep in your mind that the pain is temporary, unless you do something very stupid and get crippled for the rest of your life. I remember i feared falling after the dash vault, and never could do it right, until i hit my knee in the iron bar i was vaulting, i fell and couldn't run for a week, but when i healed, i said to myself: "i only fell because i was afraid, and i won't let it happen again". Almost never missed it again.
-diving kong: try to keep your arms straight and push yourself forward, you will push yourself upwards if you do this, so your knees will pass far from the bar.
-speed vault: try training vaulting one-handed, this will give you confidence to do it, then start trying to speed vault over bars or walls that are not higher than your waistline, and go increasing as soon as you feel confortable with the wall you're vaulting at.
Perhaps these tips won't work for you, but for me it was just like that.
And try to increase your "upper-body strenght".
Peace.
