Spongy spongy

B

bluepain

Member
Good morning
Been having an ongoing issue with my 2.0l z4.
Alot of travel on the brake pedal and spongyness.
I'll give you a heads up on parts changed then the symptoms.
Pads and discs Changed 8k ago lots of meat on.the pads.
Had brake pipes to the rear changed 5 years back as they were rusty.
Both nearside discs seemed to be binding last year.and discs were waring inside but outside was became rusty.
Took them apart bled both of them ,rebuilt that side..
Had a little affect on the exterior discs, but didn't make them completely shiney as they should be.

Had flexible hoses changed and system bled by garage..
No change

Had nearside calipers changed possibly sticky calipers.
No change

Had the local garage do an ABS bleed
The pedal initially was better ,but overnight it went back to a soft pedal.
This has been done twice now with the same result of pedal travel.

Strange symptom or i find it strange curious//.when brakes are bled with ignition off ,pedal is firm,
When the ignition is turned on,the pedal then goes soft..?

Tried a few emergency stops ,with the long travel pedal and ABS can be felt working through the pedal and it will lock up..
But it don't have trust in them like before.

Any thoughts people

At my witts end with trying to work out
 
The only thing I’ve had that match your symptoms is air in the system

When sat still with engine running can you describe the brake pedal travel and feel-

Does it start ok and get progressively spongier/longer or is it hard to start and gets soft?
 
The fact that bleeding initially cured it does sound to me like air somewhere.
I assume the fluid level isn't dropping at all?

Usually if there is air in the system, giving the pedal a few pumps (like cadence braking) can firm it up again.
 
Could check/replace the master cylinder?

If you are happy with everything of pads, calipers, discs and lines, and are confident you've done a proper bleed including the abs system, and you arent losing fluid, there's not a lot else left in a braking system...
 
When I stated soft I mean the pedal drops slowly when ignition is turned on .
Without ignition is off the pedal is as it should be with no travel.
Something I haven't checked Is trying with the engine running .
And when the only ignition on.

It's a very strange feeling to drive the car when I test drive it..very untrustworthy feeling
 
bluepain said:
When I stated soft I mean the pedal drops slowly when ignition is turned on .
Without ignition is off the pedal is as it should be with no travel.
Something I haven't checked Is trying with the engine running .
And when the only ignition on.

It's a very strange feeling to drive the car when I test drive it..very untrustworthy feeling
Click to expand...
That's a bit odd. With a master cylinder seal you would expect it to drop regardless of ignition on. It's simply pressure applied from the pedal.
Only thing I can think of now is the ABS/DSC unit is powered up when ignition is on. So maybe something happening inside there?
 
Troubleshooting from the other side of the ocean, so take it with the proverbial grain of salt -

When did the trouble begin ? with the replacement of the rear brake lines ? My Bentley E46 and E9x manuals specify to be bench-bleed the master cylinder before installation and keep it free of air during installation. The implication is that in-car bleeding is hard to get right . . . .

But I am more suspicious of air in the ABS unit. I see that the ABS bleed was done twice - is that done twice by the same shop ? I don't mean to "throw them under the bus" (is that metaphor used in the the UK as well ?), but air in a brake system can seem almost alive and willfull when it doesn't want to leave. I replaced a 3-series master cylinder once, and it was the most expensive miss-diagnosis I've ever committed. If the shop has been doing software-triggered ABS bleeding, it might be worth a try doing it the poor man's way: 1) Find an icy or gravel parking lot and make a series of ABS-engaging stops, 2) fully bleed of all four corners in proper order, 3) check the result, 4) repeat until #3 is satisfactory.
 
Maybe air in the DSC unit ?..on later cars E89 needs an ISTA process to purge it..quite some effort to do properly..
 
I'm currently going through exactly this on my Volvo having replaced both front callipers (during which, my pressure bleeder ran out of fluid, which caused the sinking pedal), and here's what I have...

- pedal sinks easily with engine running
- pedal seems hard with engine off (but I suspect it's just lack of vacuum)
- brakes bled twice by a garage, and several times by me (pressure bled, two person method, and vacuum bled including activating the ABS pump via the Volvo software)
- bled the ABS unit (by cracking the pipes loose with a pressure bleeder attached)
- with the outlet ports on the master cylinder blocked off - pedal solid
- I've therefore concluded it's the ABS unit (only £30 for a replacement, so no harm in firing the parts canon in this case). I have a new one arriving later today (in the Volvo case, it's linked to the car's immobiliser, so I need to swap the new valve body onto the old control module)

Z4Mariner said:
"throw them under the bus" (is that metaphor used in the the UK as well ?).
Click to expand...
Yep :)
 
Good people of the z4 forum..
It's been a while since I originally posted this but I thought I post the what rectified the issue ..
I posted of long pedal travel,with brakes working(poorly) with all ABS functioning and no fault codes.
After changing lots of stuff.
The issue turned Master cylinder.
After changing this and afew bleeds i have brakes once again..
 
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