Ok, so ill start off with the basics.

08 Grand Touring. Brembo brakes with VDC, drilled and slotted stoptech rotors.

noticed starting to get a soft pedal. checked have roughly 50-60% life left on my brake pads, check the fluid level and its just below the full mark, inspect for any signs of leaks, and don't like the look of on of the brake hoses, so i ordered braided stainless lines. installed the lines, bled the system several times with no air coming out, used a pressure bleeder as well as did the old fashioned manual bleed process. still have a shitty feeling pedal, decided its probably a bad master cylinder. replaced it re did the pressure and manual bleed process and still have a shitty pedal....

here is the issue. the first 1/2 of the pedal travel is super soft and like there is no brake pressure being applied, then the pedal is solid, but the car DOES NOT want to stop. i can push as hard as i want and the car has no change in how hard it stops. (same problem on both master cylinders)

No codes in the ABS system, and with a scan tool i can activate all the valves in the ABS pump, and they all seem to work normally, so i don't want to say the ABS pump has failed, but i'm out of options.. i can't seem to find any other explanation...

i have ordered another master cylinder in fear the new one i got was just defective....

anyone have any ideas?

 

You're certain there are no leaks and no air?

 

i have no leaks anywhere, have been fighting the issue for over a week now, have tried every thing to get all the air out of the system, i get solid fluid out, no air bubbles at all. have tried tapping the calipers with a rubber mallet while bleeding, like i said i've used a pressure bleeder, and the old fashioned pumping the pedal, and i cant get it working.

 

Pain to get the air out , takes multiple times.

 

^^ have gone through 14 bottles of fluid, over the past week...

 

Once it's clean fluid, bleed it into a clean container and recycle it back into the master.

I find that using the motive bleeder and someone pumping is the best way to get tricky air out of the system.

 

yeah i started recycling the fluid, ive bled and bled this thing. im not getting ANY air out what so ever guys.

 

Do you have the motive bleeder? if not get one and repeat what the process.

 

no i do not have the "Motive" brand bleeder. have a factory pressure bleeder. same thing, just connects to an air line vs having a pump.

 

I just reread your first post, Try changing the pads and see if that gives you a more solid feel after you change out your MC again.

 

leaning towards a failed ABS pump.... with the car off i have a great pedal. as soon as you start it the pedal goes to ****.

 

That is air, as mentioned , PITA to get out. I've had to bleed a car every couple days for a week to get it fully out.

 

i dont think it is air. im not getting air from any bleeder port, have been fighting this for almost two weeks now. and the pedal doesnt go to the floor, only falls about 1/2 way like the fluid is bypassing in the abs pump.

 

ended up being a failed vacuum booster...

 

Just reading through many threads as I'm having a very similar issue, what is the vacuum booster?
Many thanks.


Edit:
Ah something like this right?
http://www.z1motorsports.com/350_g35...oducts_id=4280

 

no, it is usually a bad check valve.

THats what my problem was. Wasted money on a new brake booster but only needed a 2$ check valve

 

I do the suck and blow () test on the pipe that goes to the upper plenum, I can't see where the second piping is though ?

 

I bought a new 10mm check valve today, as a just-in-case precaution.
I'll take a look at it on thursday, swap out the main one I can see.

How long should a stock valve last ?