TechyInAZ

So I've been having this problem with my RX 300, every now and then the brake pedal would have an insane amount of travel, some days it is perfectly fine. (on the days it's bad, I can floor the brake pedal all the way to the "firewall" without a problem.)

And with this issue, brake performance would drop a lot. Maxing out the brake pedal I couldn't even get close to locking up the tires or for ABS to kick in.

But if I leave the car in PWR mode, for some reason the brakes respond a whole lot better. Not sure why.

Nad1370

Possibly a leaking brake booster or an internal leak in the master cylinder.
Our brakes get assisted by engine vacuum.
There's a hose from the intake manifold to the brake booster.
I have no explanation yours get better in pwr mode. lol
Maybe holding it in higher rpms create more vacuum so you get more power assist.
But its just a guess.
I had to replace my bro-in-laws 99 when his pedal went to the floor. (brake master)

TechyInAZ

Yeah in normal mode, if i rev up the RPMs my braking performance is a lot better.

So it could just be a leaky hose?

Nad1370

Possibly or could be the booster itself.
Hoping its the hose since its a cheap fix.
OEM Boosters however might cost you a couple weeks dinner. lol
Ebay might go cheaper but its a gamble.
There is also a paper gasket in between the brake master and the booster.
That could also possibly leak.
Spray some carb cleaner around the area that you might think its leaking vacuum with the engine running.
If you hear the rpm's go up, there's your leak.
Have someone nearby with a fire extinguisher just in case. lol

salimshah

Pedal going all the way to the floor is a hydraulic failure.

Check for leaks at each slave cylinder and brake booster. Some time the leak happens inside the booster (and booster must be replaced). So look for drop in the master cylinder [the leak and drop go hand in hand]. If there is no leak or loss in level, then you can conclude that the master cylinder is bad.

Note: You should always be able to slide left foot toe when the brake is applied by the right foot. When engine is running with each successive pump of break pedal, you should notice that the travel stop should move up a bit.

Salim