Here's Sifu Lamar Davis II's answer:
"Re: Difference btwn Jun Fan Gung Fu and OJKD November 12 2003, 4:26 AM
Hello!
Well, first of all, it wasn't his back injury that caused the creation of Jeet Kune Do. It was his fight with Wong Jak Man in Oakland that brought about the changes.
Jun Fan Gung Fu is basically Bruce Lee's version of Wing Chun. It consists of a bai jong position that is approximately 70/30 0r 80/20 weight distribution (depending on who is teaching it), with most of the weight on the rear leg. Footwork is primarily forward and backward push shuffle and left and right sidestep. The primary hand tools are chung chuie, bil jee, choap chuie and qua chuie. The primary kicks are jik tek, juk tek, oou tek and hou tek. There is much emphasis on four corner lin sil die dar. Don chi sao and seong chi sao are the primary energy/sensitivity drills. There is basic and compound trapping hands, consisting primarily of pak sao, lop sao, fook sao, boang sao, huen sao and jut sao. There are entering methods such as chop chuie/qua chuie and jik tek/bil jee. Jik chung chuie (the straight blast) is practiced continuously until it becomes ingrained into your neuromuscular response system. There is more, of course, but these are the basics.
Jeet Kune Do is more alive and free, with great emphasis on mobility, speed and intercepting the opponent's initial movement, or even their intention to attack. The bai jong is 50/50 weight distribution, and the rear heel is raised. There is much emphasis on quick, explosive footwork and evasive tactics. Basic hand tools are the chung chuie, bil jee, qua chuie, ping chuie, jao sao and oou chuie. There are eight basic kicks (jik tek, juk tek, oou tek, hou tek, qua tek, juen tek, so tek, dum tek). There is great emphsis on explosive gap closing, emphasizing fast, powerful lunging attacks. The primary principles emphasized are longest weapon to nearest target, power side forward, centerline preservation, hammer principle, constant forward pressure, visual focus, economical structure and no passive moves. The primary energy/sensitivity drills are don chi sao, seong chi sao, cross energy drill, lop sao cycle drill and harmonious spring drill. There is great emphasis on trapping, both simple and compound. Bruce Lee's Five Ways of Attack are always prominently emphasized (SDA, ABC, HIA, PIA and ABD). There is much use of training equipment such as the focus glove, air shield, shin guards, double end bag, heavy bag and the mook jong. There is much sparring with protective gear to develop timing, distance awareness, power transfer in movement, evasive skills and striking accuracy.
There is much, much more that I could go into here, but this should give you some ideas as to the difference between Jun Fan Gung Fu and Jeet Kune Do."
It really clears things up.