Either a serious leak or master cylinder failure. Or if you are lucky low fluid level in the reservoir. If the latter it will want bleeding as air will have been introduced. A mobile mechanic will avoid recovery charges to a garage.
i support those who say,
external brake fluid leaks -master/hoses/lines/calipers-drum cyl(app) abs/traction controll moduals(app).
or internal leaks on master cylinder(-less *likely* an abs/traction control modual internal bypass).
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there is the possibility the pads/shoes(app) are worn to the point that the master resiviour is depleted of fluid. but that's not normally the case. as masters typically hold enough fluid (proper level) for that to happen w/o depleting the resiviour.
DIY,
for external leaks, locate the brake master cylinder on fire wall. locate and follow the lines/hoses to and through any subsystems to the brakes themselves. then feel the inside of the wheels/rims. on the flat spot of the wheel. iffin a brake cyl or caliper is leaking, there will be evidence there.
tackyness can imply and external slow leaks that's being wind dried as one drives..
there's a small possibility the master is leaking through the booster. but not likely w/o effecting engine performance. as that would denote fluid making it's way into the vacuum system. and plugs, regardless of ignition systems, can not burn brake fluid. it will foul plugs.
opening the brake master cylinder fluid cap, have someone depress brake pedal. you see a guiser of fluid, the master is in bypass internally.
lot of possibilities to swallow there. soory. but that should cover most all possibilties
USAF trained hyaulic/pneumatic tech. fleet service 3yrs. racing and wrenching since 1968.
the most likely cause's - the master cylinder failed, brake cylinder failed, brake line broke, caliper failed, if air did get in the system then it must have been leaking fluid somewhere to let the air into it, but, I do not think it is the case here, in any case the repair or replacement of the items noted above does not entail a great deal of work, but you must have some knowledge of the system in order to fix it as you will need to bleed the system once it is fixed!
Driving home tonight I was coming up to traffic lights and braking as normal when all of a sudden the brake pedal went right to the floor and i had no brakes. Had to use the handbrake to stop. Could it be just air in the lines or something more serious.
