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Inconsistent and spongy brake pedel feel.

lars3010

New member
Location
Germany
Car(s)
2018' Audi A5
I took it to heart to activate the ABS by braking more frequently on loose asphalt. After that, the pedal felt somewhat okay. I then bled the brakes again, and a few air bubbles came out. Later, I went for an extensive test drive, but the pedal became noticeably worse again. In certain driving situations, the pedal brakes as it should. You then try to pump it because you think the pedal feels soft, and unknowingly end up fully engaging the brake. This happens sometimes at irregular intervals. With the next braking, it feels softer again.

I would really like to figure out what could be causing this… Whether there is still air in the system, which might be slowly reintroduced through some kind of valve.
 

Jcris

Passed Driver's Ed
Location
Lakeport, Ca
Car(s)
2016 GTI S 2.0T
Nothing has worked (long-term) so far. Occasionally replacing a part or bleeding will result in an improved pedal feel, but it never lasts more than a day or two. As of now, the car has had a second master cylinder replacement and new front pads and discs, provided by VW. I have also replaced the rear pads, lines, rotors, and calipers. I had assumed that the black material that would appear in the brake fluid at the rears was somehow related to the rear, but even with those new parts I'm still seeing the black fluid. Not sure where it could be coming from, other than the ABS unit. After I raised absolute hell with the dealership and the VW rep they sent down, they agreed to order and replace the entire ABS unit. I'm not sure what else it could be, and honestly, if this doesn't fix it, I'm done with it.
You ever get this fixed?
What an frustrating scenario.
I can’t believe the bs you’ve gone through.
Did they ever replace the booster? I’m not sure how that relates but how in the f…ing world can’t the dealer figure this out?
 

woodardhsd

Go Kart Newbie
Location
NC
Car(s)
2019 GTI Rabbit CFB
Not yet, still waiting on the ABS module to show up. It was supposed to be here a couple of weeks ago.

The booster was the first thing the dealership replaced.
 

victorofhavoc

Autocross Champion
Location
Kansas City
Not yet, still waiting on the ABS module to show up. It was supposed to be here a couple of weeks ago.

The booster was the first thing the dealership replaced.
Just for future reference, you can turn the booster up and down in the registry with obd eleven or vcds. I had spongey brakes on track when I tried to reduce the booster while following some modifications people posted for "more linear brake feel". It was entirely wrong and caused all sorts of issues before I moved it back to stock. Playing with the booster did point out where my issues were though.

Doesn't sound like your issues but for others' reference, my spongey brake issue was a result of pad knock and crap disc thickness variation (dtv). Ultimately, I found brushing the brakes before applying them to resolve most issues, but you can always install a one way valve on the brake lines. Technically floating calipers are less susceptible to pad knock, but if the pins are warped, not well lubed, gunky, or over torqued you will have knock issues. Mine were over torqued (my fault) and warped (heat's fault).

Pad knock is very unlikely for street use unless those pins are in terrible shape or your disc is really bad, though.
 
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