Spongy brakes, I've done EVERYTHING...

[lcoleman]

I have a spongy brake pedal, doesn't feel as firm as it should. I notice that after sitting for a while, it takes a pump or two to get it to firm up (car not running). I also notice that the brakes will "pump up" while driving, so overall the pedal feel is just inconsistent.

I have gone through several master cylinder setups (e32 with regular res, 2002 res, etc etc) before biting the bullet and getting a brand new master and booster.

I have bled liters and liters (probably gallons at this point) through the system. Fluid is crystal clear. Two-man, pressure bleeder, even "crack the line and pump 21 times" per the ancient TIS (this works because the ABS pump acts as a check valve.

My thoughts:
1. Bias valve--can this go bad and cause my issue?
2. Air trapped in ABS. My ABS light is out of the cluster, and afaik it hasn't worked since I bought the car. Does removing the light disable the system? Would jumpering the relay in the fusebox like I've read about be of any benefit?
3. Pads worn unevenly, causing caliper to bind. I know the pads are ever so slightly worn at an angle, because they've been run aggressively in the past, but so have other sets of pads and I didn't have any problem with those. My braking force is also perfectly fine, once you push down far enough.


Please, share any thoughts or insight or criticism you may have. I am extremely frustrated with this--I want good brakes back!

[Holland]

Sounds like your calipers or pads to me. If a caliper is sticking, or clogged with dirt, it's going to operate poorly. Some pads have also been known to feel spongy compared to others.

[lcoleman]

I have considered this, but would pads "pump up" like that?

[bmwguy325is]

I would say go out and complete several ABS stops.
Then bleed the system with the car in the run position so the ABS pump gets power.

[kronus]

have you considered replacing your brake sponges with brake pads?

more seriously, have you rebuild or replaced your calipers?

[bowtie2bimmer]

Kind of a stretch but lines? They expand and over time get softer so you will lose pressure...

[lcoleman]

ABS does not work, as far as I know. Can I jumper the relay, and then bleed? I have read in one place that works, but I'd like to hear it from someone else.

Pads are Hawk Ceramics, they were good before being shelved for about 6 months.
Calipers are original, but worked great before the MC/pad change.

Lines are BW stainless, a few years old. Another thing that worked great before the parts got change.

I have considered new pads, rebuild all the calipers, and get new OE lines, but spending that much money and time is a last resort for this. It really, really feels like air to me, especially since I can pump up the pedal after the car's been sitting.

[lcoleman]

No one knows how to bleed the ABS pump?

[808e30325i]

Your abs working or not isn't going to cause that big of a diff in spongy feel. it would be more of "air in the system"/ or even old rubber lines that expand to cause a spongy pedal. 1st-after changing all those master cylinders did you correctly bench bleed them before install?

[5Toes]

do a bunch of hard stops to get abs to cycle on

[WhyNot]

My thoughts:
1. Bias valve--can this go bad and cause my issue?

i dont thinx so but the proprtioning valve may be suspect since you say "My braking force is also perfectly fine, once you push down far enough"

2. Air trapped in ABS. My ABS light is out of the cluster, and afaik it hasn't worked since I bought the car. Does removing the light disable the system? Would jumpering the relay in the fusebox like I've read about be of any benefit?

probably not, most probably not, dont thinx so

3. Pads worn unevenly, causing caliper to bind. I know the pads are ever so slightly worn at an angle, because they've been run aggressively in the past, but so have other sets of pads and I didn't have any problem with those. My braking force is also perfectly fine, once you push down far enough.

probably not, slight angle is nothing.

Please, share any thoughts or insight or criticism you may have. I want good brakes back!

you are a worry wart. downshift and use the parxing braxe.
my laptop has no letter after 'j' so i use the x instead












1st guess...
if the wheel bearings have play in them, when they wobble they can push the caliper pucxs bacx in the bore.
then when you hit the pedal, alot of the travel is to getthe pucx bacx out.
with tire in air, grab top and bottom and see if there is play
2nd guess...
the orings in the master cylinder are starting to go.
when you pump they sort of swell up.
to test, with car stopped and off, put a small amount of pressure on the pedal.
it should hold. if it falls slowly the mc is bad

[lcoleman]

Your abs working or not isn't going to cause that big of a diff in spongy feel. it would be more of "air in the system"/ or even old rubber lines that expand to cause a spongy pedal. 1st-after changing all those master cylinders did you correctly bench bleed them before install?

No. I have bled from the lines at the MC itself, though. Lines are Bimmerworld SS, a few years old. Braking feel was fine before the pad/MC swap. I have bled literally gallons through this system. If there is air, I need to cycle ABS to get it out. ABS doesn't function, so I need to know how to cycle the pump manually.

i dont thinx so but the proprtioning valve may be suspect since you say "My braking force is also perfectly fine, once you push down far enough"

This will cause a pedal that needs to be pumped up?

you are a worry wart. downshift and use the parxing braxe.

Ghetto suggestion is ghetto? I will be driving this car in anger once the brakes are sorted, ignoring a mushy pedal is not an option here.

1st guess...
if the wheel bearings have play in them, when they wobble they can push the caliper pucxs bacx in the bore.
then when you hit the pedal, alot of the travel is to getthe pucx bacx out.
with tire in air, grab top and bottom and see if there is play

I think that to be this bad, the bearings would have to be really, really bad. I would notice.

2nd guess...
the orings in the master cylinder are starting to go.
when you pump they sort of swell up.
to test, with car stopped and off, put a small amount of pressure on the pedal.
it should hold. if it falls slowly the mc is bad

It's brand new. The pedal has to be pumped once or twice with the car off after sitting to get good pressure.

[808e30325i]

my guess is that you have a huge air bubble trapped at the forward end of the mc. you need to take off the mc and do a proper bench bleed before you go any further.

[WhyNot]

good suggestion above.
also prop valve might stop pressure from flowing right so it might seem lixe its something its not.
the downshift was just a bad joKe.
youre wrong about the bearings. i little play causes the pedal stroxe to get the piston to where it should be.
if someone is maKing a suggestion shouldnt you maybe try it before you tell them theyre wrong?

[jlevie]

Air in the ABS unit is a possibility. I've never had that problem, but you should be able to active the ABS unit with jumpers. See the wiring diagrams at http://wedophones.com/BMWManualsLead.htm