I have a 1999 Yamaha v star 650 classic can I modify it to use both brakes by only squeezing the front brake lever at the handlebars
You would need to put a larger master cylinder and an adjustable pressure regulator on the rear line but you could do it I have a sidecar and st up the rear brake pedal to operate the bikes rear wheel and hack wheel together.
Combined braking is rubbish and dangerous, and it should be removed! I would NEVER buy a bike with it on, because as James says there are times when it's DANGEROUS to not be able to use the brakes independantly. The way you want to do it is even more dangerous, as combined brakes only activate part of the brake on the other brake, whereas you want to make a car-like system with one lever for all the braking all round! It would also take you longer to stop in an emergency due to not being able to get the full amount of pressure at the front without locking up the back.
No, that would be very dangerous. Combined braking systems use complex electronic controls and hydraulic proportioning valves to get the right ratio of front/rear braking for various conditions. Any DIY system is highly unlikely to get it right, and the probable result would be loss of braking control at a critical moment. There are also times when you NEED to use the brakes independently, such as braking when turning at low speeds, or starting on an uphill grade.
