Brake pedal goes to floor

[grayeagle57]

Im having an issue with the brake pedal going slowly toward the floor after stop, allowing the car to start creeping foward. Im thinking its a master cylinder issue. Any comments?

[1990LS400]

Do not drive it.  Call a tow truck (flat bed only) and have it taken to a Lexus dealer or independent repair shop.

[curiousB]

Hi gang,

 

Haven't posted for a while so hello again to all.

I'm having a similar brake problem but not as severe as OP. My pedal is a bit spongy and if I press the brake pedal very hard I can get the pedal to hit the mechanical stop. The car never creeps though and brakes stop ok. The brakes just seem grabby. If I tap the pedal quickly they seem to grab rather than a gradual engagement and slow dow.

I did flush brake fluid a couple months ago thinking that might be it (air in lines old contaminated fluid) but that didn't seem to do much. There are no apparent leaks anywhere so I don;t have a rupture seal that I can see. I'm wondering if this is an indication of master cylinder seal worn out and fluid leaking past the seals. I have also read some folks say the flex lines to each wheel can get weak and lead to soft brake pedal ( I assume the sidewalls of flex are stretching under pressure?).

I notice it more now as I got my wife a GX470 last year and her pedal is firm and no sponginess.

I don't want to start randomly throwing parts at this. Anybody a brake expert or solved a similar problem with a LS430 (2004)?

 

 

[Sal00]

On 4/4/2016 at 10:58 AM, curiousB said:

Hi gang,

 

Haven't posted for a while so hello again to all.

I'm having a similar brake problem but not as severe as OP. My pedal is a bit spongy and if I press the brake pedal very hard I can get the pedal to hit the mechanical stop. The car never creeps though and brakes stop ok. The brakes just seem grabby. If I tap the pedal quickly they seem to grab rather than a gradual engagement and slow dow.

I did flush brake fluid a couple months ago thinking that might be it (air in lines old contaminated fluid) but that didn't seem to do much. There are no apparent leaks anywhere so I don;t have a rupture seal that I can see. I'm wondering if this is an indication of master cylinder seal worn out and fluid leaking past the seals. I have also read some folks say the flex lines to each wheel can get weak and lead to soft brake pedal ( I assume the sidewalls of flex are stretching under pressure?).

I notice it more now as I got my wife a GX470 last year and her pedal is firm and no sponginess.

I don't want to start randomly throwing parts at this. Anybody a brake expert or solved a similar problem with a LS430 (2004)?

 

 

I know this is old but this is exactly the issue I have, the brakes stop perfectly but go to the floor if I press them hard at a stop

[RX400h]

Most of the time, the culprit is one or two things:

1. Air in the brake lines - requires a thorough fluid flush

2. The master cylinder seals are worn. This can be due to age/frequency of use or when someone bled the fluid, he had someone press the pedal all the way to the floor, repeatedly. Your master cylinder piston typically travels approximately half of the total distance. Over time, the cylinder can wear up to that point, leaving a "lip" in the cylinder wall. When someone pushed the pedal to the floor to bleed the system, the piston seal can be damaged, resulting in leakage.

Start with #1 to see if that fixes the problem.