at high speed or RPM for extended periods of time my brake go to the floor. the car stops and they work but if this is a boosted brake car it's like the boost is gone and brake goes in a LOT further than it normally does. thoughts? they pump right back up when i let out of it and or coast for a bit.

 

You're losing vacuum. Less is created at high rpm.
Sounds like booster replacement time.

 

definitely the brake booster, the diaphragm is busted.

 

i think it's leaking more than busted since it doesn't do it all the time 100% consistent but, i'm sure after 13 years the rubber in booster or the diaphragm or hose has crack. are there any hoses going to the diaphragm?

 

BRAKE BOOSTER OPERATING CHECK
1. Stop engine and depress brake pedal several times. Check
that pedal stroke does not change.
2. Depress brake pedal, then start engine. If pedal goes down
slightly, operation is normal.

BRAKE BOOSTER AIRTIGHT CHECK
1. Start engine, and stop it after one or two minutes. Depress
brake pedal several times slowly. The pedal should go further
down the first time, and then it should gradually rise thereafter.
2. Depress brake pedal while engine is running, and stop engine
with pedal depressed. The pedal stroke should not change
after holding pedal down for 30 seconds.

 

Possibly brake booster or vacume like previously stated but if you've had your brakes done recently you may also want to try bleeding the lines and checking for any small leaks.

 

Then it wouldn't be assisted if the vacuum was leaking the brakes would be hard.....I think it's your MC! Make sure your have no leaks...in the system period! Fluid disappearing? If not I bet my nuts on the Master Cylinder (MC)...

 

CMax, You hope George doesn't see this or he might go to collect on that lol.

 

I agree, but why only when at higher rpm?

Maybe both are bad.

 

yeah i'll do that check. i can't remember any one single time it's happening during normal city driving. you like 15-45mph driving. also the snap-on verus is reading a REAR wheel sensor that is saying something like 150-250 mph. not sure if a sensor or the verus.