Brake pedal goes almost to the floor on a 2004 Toyota Sienna Van. Seemed like defectice master cylinder. Replaced master cylinder with same results after multible bleed attemps

Brake line busted somewhere? Is the linkage to the master cylinder intact? Master cylinder might have been installed incorrectly.

is the abs light on?the abs system only effects the pedal when you are stopping quickly to activate the system. you still have a hydrualic brake pressure problem. are the rear brakes shoes or pads? rear shoes out of adjustment can cause a low brake pedal.even though the master cylinder has been replaced doesn't mean you got a good part.if the part was a remanufactered part very likely it is bad. to determine if it is the master cylinder, plug off the lines from the side off the master cylinder and hit the brake pedal. if the pedal stays up look for a problem elsewhere in the system. if the pedal drops the the master cylinder is defective.

This sounds like a bad master cylinder, are you getting a brake light?

i have had several sequoias and tundras in my shop with the same complaint , i think its an issue toyota knows about but doesn't want to admit , i think they dont know how to fix it ,although in one instance we got a code for the master cyl psi switch and the customer states after we changed it the "no brake pedal " went away

Sounds like there is a fault with the vacuum pump not generating enough vacuum for the brake booster assist, or a leaking vacuum hose. Try pinching off all the vacuum hoses to see if the problem goes away. Could also be a leak in the brake vacuum booster itself

your brake booster had developed a vacuum leak internally, likely the diaphragm. this is a sealed unit, so the entire part must be replaced. this is the large round canister located behind the master cylinder (very difficult to see and access on your van). good luck!

Start with brake in the rear that is the farthest away from the master cylinder ( if your master cylinder is on drivers side start with passenger rear,pump up brake pedal until hard have someone else open bleeder valve until air or fluid squirts out,while holding brake pressure even if goes to the floor dont release pedal until bleeder valve is tightened or you will **** air back into the line,do this several times making sure you get a full stream of brake fluid and no air,continue to other rear wheel and then proceed to front wheel furthest from master cylinderand then final wheel. if you still don't have brakes change master cylinder and bleed all brakes again.

double check fluid.you have air or are losing hydrolic pressure somewhere. leak in master cylinder can do this. also vacume and air leak in the booster unit. double check bleading points on each wheel.

there is still air in your hydraulic lines somewhere bleed the system with a pressurised power bleeder and you will get instant results

You have to check your master cylinder, pump your brake several times and hold it, see if is going down to the bottom, if does, the master cylinder is wrong, check the brake pressure hose, maybe you have some air in your brake lines, be sure you have enough brake fluid