Inconsistent and spongy brake pedel feel.

[lars3010]

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]

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]

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]

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.

 

[SnowCone]

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.

Any update here?

I'm getting the same symptoms as you (spongy/low pedal, slowly drops to the floor under decent pressure at a stoplight) with a somewhat sudden onset a few thousand miles ago. Everything was fine after I did new pads and rotors about 15k mi ago, with a full flush with a pressure bleeder.

I plan on bleeding everything this weekend as a first step, but I'm not sure how air would suddenly end up in the system.

Mine is a 2020 GTI manual with about 79k on the clock.

 

[woodardhsd]

Not yet, still supposedly waiting on the ABS Module. It's now been close to 6 months since they ordered it. I'm starting to think they are trying to run out the clock on my warranty.

 

[victorofhavoc]

If you're getting pedal drop while stationary, it's almost always the abs pump.

2 other cars I've had began pedal drop when the pump started to go...

 

[SnowCone]

I bled the four corners this weekend with a pressure bleeder. I got zero indication of any air while bleeding (no bubbles). On test drive after, the pedal seemed to feel worse if anything, but after driving a bit it is the same or slightly better than before. Still a low pedal to varying degrees, and the pedal still sinks very slowly at some stoplights.

Looking forward to hearing what the ABS module does for @woodardhsd , but otherwise my plan is to get mine to a VW/Audi specialty shop near me and see what they think.

 

[woodardhsd]

Looking forward to hearing what the ABS module does for @woodardhsd , but otherwise my plan is to get mine to a VW/Audi specialty shop near me and see what they think.

Don't hold your breath. Still waiting on the ABS module that they ordered in November. At first I thought they were screwing with me, but have since reached out to a couple different parts departments/suppliers who confirmed that the module in on backorder with no estimated delivery date. At this point, I'm seriously considering finding a gently used module and swapping it myself to see if it makes a difference.

 

[woodardhsd]

Found a low-mileage ABS module on Ebay and took a gamble on it. Got it swapped in fairly easily, but the brake lines were fighting me the whole time. There's not much room to move them, so I had to kinda tweak them a bit to have room to remove the ABS unit. Got them back in and bled, and could already feel a difference, even on the first drive. Had no trouble applying the coding to the module (copy/paste) but was still getting tons of errors. Was only able to perform the basic setting for brake pressure as I couldn't find the other 3. It drove OK, but had no ESP, cruise, TPMS, auto start/stop. After some help on the Ross Tech forum, I performed the ESP basic setting, as well as the TPMS reset. That got rid of all the lights and codes.

It probably needs one more good two-person bleed, along with some ABS stops, to get the last of the air out, but the pedal seems much firmer than before. I've been here before, but I'm cautiously optimistic.

 

[DerHase]

Open VCDS or OBD11 and look for values pertaining to the brake booster vacuum levels.

When the pedal is feeling like it's sinking, see if it is actually the vacuum pump not keeping up with your pedal demands.

If you shut the car off, pump the pedal multiple times, then start. Does (the tail end of) this replicate your spongy pedal feeling?

I've logged this stuff a while ago and it takes a LONG time for vacuum to fully build.

Snipped from an article of mine regarding adaptations.
https://docs.google.com/document/d/1ituwUxAf7676mMw06GSneVTrfapKjTXSKKoxa933cPY/edit?tab=t.0
https://www.datadrivenmqb.com/brakes/brake-adaptations

 

[blackwind95]

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.

I echo lubricating or greasing up the caliber pins. Does improve the brake pedal feel. Use proper grease for the application and lookup Youtube on videos for tips.