LGT brake pedal slowly to the floor?

I apologize if this is a n00b question, but here goes.

 

My Legacy is the first ABS equipped car I've owned. So I'm not sure if this behavior is ABS related, crappy brake lines/fluids, just the nature of the beast.

 

So I've got my foot on the brake, and I'm pushing down to what I would call full brake engagement. Then if I keep pushing the brake pedal will keep moving down. As long as I keep pushing, it will keep moving. (Literally down to the floor)

 

In my Nissan/Miata/etc. when depressing the brake, the hydraulic system reached a certain amount of compression, and it stopped. The brake pedal wouldn't travel any more regardless of how hard I pushed.

 

I'm wondering if this is hte sponginess people talk about from the rubber brake lines, or if this is some ABS specific valving that pushes hydraulic fluid back into the resevoir if the pedal is pushed to hard, or what.

 

It feels like a.) the lines are expanding or b) the pressure is being rerouted somewhere else (either to the reservoir, or out to the atmosphere somewhere.

 

Any ideas?

 

--james

I would think you have a problem. I'm thinking about the last time im in my car and the pedal is a lil mushy up top but then frims up at about 60% engagement and then the feedback on the pedal is enough that unless you are emergency breaking you dont go down much more, I'll pay more attention when i drive my car today, but i dont ever recall my pedal going to the floor (other then the gas and the clutch :lol:)

To clarify, the brakes do engage and they do work. For instance, turn the car on, put it in neutral, and then just keep firm pressure on the brake. It reaches the "locking point" (where the pads are in contact with the rotor), but it just keeps moving down. I haven't seen any fluid loss or anything, so I don't *think* its leaking.

Thanks for the response.

 

--james

sounds like you have a leaking master cylinder seal. if you are keeping steady pressure on the pedal, it should stay put for a while.

I mean if I step on the brakes...then turn on the engine...the pedal will sink a bit. And with the engine on there is a limit to how much I can depress them and it will not get harder no matter how many pumps I do.

 

Do this: turn off the engine and pump the brakes. if it takes more then...2-3 pumps to get a completely stiff brake pedal...then you got a problem and somewhere you got air in the system.

I agree with bugblatterbeast.

 

This is almost definitely a leaking master cylinder. I've had this happen to two of my older cars. Usually, it happens sometime between 120000 and 170000 miles.

 

In one of my older cars, the master cylinder was damaged when my friend pumped the brakes incorrectly (a little bit too vigorously and with air ... etc...).

 

It usually doesn't matter whether it's ABS or not since the ABS system is an additional unit separate from the master cylinder.

jholder, if i understand what you are describing, once you are already stopped with the brake pedal depressed, if you press harder on the pedal it will start to sink lower. I've had the same experience with my stock brakes. I also have the sinking pedal with StopTechs in front and stainless lines front and back.

 

edmundo explained it as: "The reason you're feeling the pedal sinking is due to the vacuum booster, not a defect in the MC."

 

so i think if you are experiencing the sinking pedal when stopped, it is normal.

Mine behaves the same way....... strange....

 

No issues with actual braking... I've just noticed the same phenomenon with my car.

i have the same problem, but if i get the abs to engage it will firm up quite a bit for the next few days. also i noticed that when the abs engages the car has a tendency to slide to the left hand side.

Mine behaves the same way....... strange....

 

No issues with actual braking... I've just noticed the same phenomenon with my car.

Me too, happend today

jholder, if i understand what you are describing, once you are already stopped with the brake pedal depressed, if you press harder on the pedal it will start to sink lower. I've had the same experience with my stock brakes. I also have the sinking pedal with StopTechs in front and stainless lines front and back.

 

edmundo explained it as: "The reason you're feeling the pedal sinking is due to the vacuum booster, not a defect in the MC."

 

so i think if you are experiencing the sinking pedal when stopped, it is normal.

 

That's exactly whats happening. It brakes fine, and I come to a stop. Keeping steady pressure on the pedal causes it to sink lower and lower. Its just a really wierd feeling when you're used to a pedal that firms up in relation to how far the pedal is depressed.

Not a probelm.

Bleeding the brakes helps

Bleeding the brakes helps

 

I don't think there is air in the line. the brakes engage fine, its once the pads are engaged, that the problem arises. One of the posters mentioned the brake booster getting vacuum happy. Thats sounds like a reasonable explanation for what is happening in my case

My euro-sped 2007 Outback 3.0R with 13K miles does the same thing. It brakes fine and the pedal holds position when I apply constant pressure. But if I start to add more pressure it will sink deeper and with enough pressure it will sink right down to the floor.

Update:

 

Took my euro-spec 2007 Outback 3.0R with 13K miles to the Subaru distributor's HQ in Taiwan. They checked the MC, calipers, pads, lines and stuff. Even put the car on brake dyno to check the stopping power of each individual brake and they were all within spec.

 

So we went to the new car storage lot and pulled out a brand spanking new 09 Outback 3.0R with VDC for comparison and both cars' brake pedal can be literally floored when the engine is running.

 

I shrugged and left the shop knowing the car is not broken.

 

Now I am split between Brembo F50 4pot + 330mm solid disc, AP CP5200 4pot + 330mm floating disc or WP-Pro 6pot with 360mm floating disc.

I have Brembos all around and my brake pedal still sinks slightly if I keep putting more pressure onto the pedal. There is a point where the brakes completely lock but the pedal continues to sink. The problem is not resolved by moving to bigger calipers and SSl lines.

I have the complete opposite issue, mine are super stiff right off bat. Is that to much fluid? Incorrect fluid?

 

New owner of a 2006 GT here. Long admirer of the GTs since i had a 94 growing up.