Inconsistent and spongy brake pedel feel.

[woodardhsd]

Looking for brake advice. Picked up a low-mileage rabbit edition back in September with a soft brake pedal. Figured it just needed a flush and bleed since previous owner didn't have that done. It didn't need it by mileage, but certainly by age. Pressure flushed and bled the system. Fluid was slightly dark and did flush out a few air bubbles, but it didn't improve noticeably. Made sure to activate the ABS a few times, and tried again. This time I also finished up with a manual 2-person bleed. Got a few more bubble out, but not a noticeable improvement. Figured I was doing something wrong, so I took it to the dealer since the car is still inside the warranty window. They seemed to think the pedal is fine, so they didn't do anything else. After another month of driving and general frustration I decided to try another dealer, this time over 2 hours away (I live in the sticks.) They agreed that the pedal didn't feel amazing, but that it was close enough that they didn't feel it warranted further diagnosis. Since the 2nd dealer appointment, I performed another pressure bleed. This time I changed up the bleed order from what the manual says, and did the more traditional order of RR, LR, RF, LF. Did get a little more air out, but only from the RR caliper.

One thing to mention is that I do notice a bit of black sediment fluid each time I would bleed the rears, but it would go away after a couple of pumps. But then it would be back the next time I bled, but only for a pump or two. I was guessing an issue with a rear flex-line or caliper, but they all look fine.

I'm at a loss here. I had a 2020 GTI before this and the pedal was nice and firm. The rabbit edition should have the exact same brakes as the 2020. I'm wondering if I have a bad master cylinder or some other issue?

 

[GTIfan99]

The abs system seems to trap air in these things. When you bleed, you need to use obd11 or similar to bleed the pump and they can be hard to bleed properly.

Search for the Macan caliper thread, it's got the correct bleeding procedure in it.

Crappy pads can also cause a weird soft feeling.

 

[GTIfan99]

Here's the thread.

https://www.golfmk7.com/forums/inde...brembo-upgrade-thread-read-first-post.371028/

 

[DerHase]

A lot of people overlook the mechanical aspect of things when trying to fix brake pedal feel.

Make sure that the pads aren't worn/tapered super badly. This will cause a spongy feeling pedal because half the pedal travel is being used to flex the pad/caliper trying to make uneven surfaces mate.

This also goes for when swapping pads if you have slightly uneven wear on the rotor vs the pad itself. Unless it's insanely bad, this generally resolves itself within a couple hundred miles of driving.

Not saying it's not a bleeding issue, but don't chase your tail without those things being verified first.

On top of that, pads themselves have varying levels of "compressibility" and some will just feel spongier regardless of what you do.

And finally, "sponginess" is subjective. If you have pads that bite really hard with little effort, even a system with a tiny bit of air in the lines will "feel" ok. Conversely, if you have pads that just plain have a really low coefficient of friction, it will be perceived as "spongy" because you are needing to apply a LOT more pressure than "expected" for the level of stopping it produces.

Cases in point:
- I've put Hawk HPS (non-5.0) on an 09 Mazda3... they SUCKED. Horrible bite, always felt awful. Got some OEM pads and all was good again. The 5.0 pads I used in another application and didn't have this issue FWIW.
- 06ish Chevy Trailblazer... Bled and bled and bled and bled the brakes. Nothing visibly wrong with any of the pads, rotors, etc. Replaced the pads with some known quantity parts store pads (Carquest Golds) and resurfaced rotors... and lo and behold the pedal was great. Didn't take tons of effort to stop anymore so as a result, it no longer felt spongy in normal operation.

 

[victorofhavoc]

I've had bad luck bleeding this car under pressure. I do it under pressure to flush it, then at the very end I do the old school pump and hold method. Sometimes a bubble really gets stuck in there, and in those cases I've had to bleed both front calipers at the same time.

Also, if the car was used, maybe make sure no one messed with the Adaptations for the booster and such. Lots of people make those changes having zero clue what they do, and a few of them can really jack with the pedal feel. The brakes on these cars should be pretty immediate with a lot of grab up front.

 

[GTIfan99]

There's an insane difference between the sponginess of my street pads vs my track pads and neither has uneven wear. I find ceramic pad material compresses more than aggressive track pad.

 

[woodardhsd]

They are definitely the OEM original pads, not anything aftermarket. I would assume that they are the exact same pads that were on my 2020. Braking performance on that car was great from day 1 (bought new) until the day I sold it. Even the brakes on my wifes Sportwagen are better than this car. That was definitely not the case when I compared it to my 2020.

The abs system seems to trap air in these things. When you bleed, you need to use obd11 or similar to bleed the pump and they can be hard to bleed properly.

Search for the Macan caliper thread, it's got the correct bleeding procedure in it.

Crappy pads can also cause a weird soft feeling.

I glanced quickly at the Macan thread and will go over it better later. I hesitated to do the ABS Bleed with VCDS because there seems to be some confusion as to the procedure itself, as well if it's even required. I've read that if you bleed with 29 psi per the service manual, or make sure to activate ABS multiple times, that bleeding the ABS pump is unnecessary. I'm willing to do whatever, just want to know the correct procedure.

I've had bad luck bleeding this car under pressure. I do it under pressure to flush it, then at the very end I do the old school pump and hold method. Sometimes a bubble really gets stuck in there, and in those cases I've had to bleed both front calipers at the same time.

Also, if the car was used, maybe make sure no one messed with the Adaptations for the booster and such. Lots of people make those changes having zero clue what they do, and a few of them can really jack with the pedal feel. The brakes on these cars should be pretty immediate with a lot of grab up front.

It was used, but I don't think the previous owner made any adaptations. He seemed pretty clueless when I showed up with a laptop and VCDS when I first looked at the car. I did a few adaptations after I bought it, but none were to anything brake related.

 

[GTIfan99]

They are definitely the OEM original pads, not anything aftermarket. I would assume that they are the exact same pads that were on my 2020. Braking performance on that car was great from day 1 (bought new) until the day I sold it. Even the brakes on my wifes Sportwagen are better than this car. That was definitely not the case when I compared it to my 2020.


I glanced quickly at the Macan thread and will go over it better later. I hesitated to do the ABS Bleed with VCDS because there seems to be some confusion as to the procedure itself, as well if it's even required. I've read that if you bleed with 29 psi per the service manual, or make sure to activate ABS multiple times, that bleeding the ABS pump is unnecessary. I'm willing to do whatever, just want to know the correct procedure.

It was used, but I don't think the previous owner made any adaptations. He seemed pretty clueless when I showed up with a laptop and VCDS when I first looked at the car. I did a few adaptations after I bought it, but none were to anything brake related.

Easiest path is do some abs inducing stops. Then do the high pressure bleed in the order specified in the thread. And make sure you don't run the high pressure bleeder dry. Drive for a few days, repeat. I also tap on the calipers with a small mallet when bleeding to help get any air trapped out.

If that doesn't work, you'll need to bleed the abs pump.

 

[woodardhsd]

Done all that. Did several abs stops on a loose surface before each bleed. First two pressure bleeds I did in the order specified in the manual (FL, FR, LR, RR) at 30psi. The third pressure bleed I used the typical bleed order (RR, LR, RF, LF), again at 30 psi. I would even beat on the caliper with my palm while bleeding to help loosen air up. I would also pump the brake pedal a couple of times with the pressure bleeder connected in between cracking the bleed screw open.

The only thing I haven't tried (other than the ABS pump bleed) is the pre-bleed procedure mentioned in the service manual where you bleed the fronts simultaneously, then the rears.

 

[GTIfan99]

I did all that and still had a soft pedal. It wasn't until I swapped pads and pushed the pistons back into the calipers that I got all the air out.

Modern cars can be a pain to bleed.

 

[victorofhavoc]

Eliminate the pressure bleeder from your setup and just have someone pump the pedal and hold. Ones less variable to deal with.

If it's the typical motiv type bleeder, I've seen issues with them when they're leaking even a bit of pressure. They're especially prone to failure after brake fluid runs through them and they're not washed/lubed after use.

 

[woodardhsd]

I did all that and still had a soft pedal. It wasn't until I swapped pads and pushed the pistons back into the calipers that I got all the air out.

Modern cars can be a pain to bleed.

I guess I could try compressing the pistons while opening the bleed screw. I'm not sure how far they'll go since the pads are still very close to factory thickness.

Eliminate the pressure bleeder from your setup and just have someone pump the pedal and hold. Ones less variable to deal with.

If it's the typical motiv type bleeder, I've seen issues with them when they're leaking even a bit of pressure. They're especially prone to failure after brake fluid runs through them and they're not washed/lubed after useI

After my second pressure bleed, I did do a manual bleed of all 4 corners. I really don't think that's the problem, but I'm willing to try anything at this point.

It is a motive power bleeder, but it's brand new. I've been using it without fluid just to pressurize the reservoir. I'm very vigilant about making sure the fluid level doesn't even get close to the minimum.

 

[victorofhavoc]

I guess I could try compressing the pistons while opening the bleed screw. I'm not sure how far they'll go since the pads are still very close to factory thickness.

After my second pressure bleed, I did do a manual bleed of all 4 corners. I really don't think that's the problem, but I'm willing to try anything at this point.

It is a motive power bleeder, but it's brand new. I've been using it without fluid just to pressurize the reservoir. I'm very vigilant about making sure the fluid level doesn't even get close to the minimum.

That's a good method with the motiv. You're on the right track.

The only other thing you could really do (besides trying to kick on the abs pump manually), is have two helpers. Keep the pressure bleeder on, have someone pump brakes, and two people bleeding the fronts while tapping the calipers with rubber mallets.

I've only had to do this once, and it was because I was in a rush and opened the wrong mc on a car i wasn't super familiar with. Sucked a gob of air and ran the whole system dry on one caliper . Lessons learned

 

[woodardhsd]

Picked up one of those caliper piston compression tools from the store and reset the pistons on both rear calipers. No additional air came out when I compressed them, or when I pressure bled with the tool still installed in the caliper holding the piston all the way in.

Then I tried an ABS bleed, but I'm not sure I managed to do that correct. From what I've read, you open VCDS, blick on 03-ABS Brakes, then 04-Basic Settings, then select Brake System Bleeding. Then it's supposed to walk you through the bleeding process. Mine looks nothing like this. I get a drop down that has many items, including "brake bleeding" and "fill/bleed brake system." I've attached screenshots of the menu when selecting either of those choices. The only thing I coudl get to work was the"first flushing cycle" on the "brake bleeding" screen. It would run the pump for approximately 15 seconds, then stop. Was never able to proceed to the next steps. I did force the pump to run multiple times with both rears open, then again multiple times with both fronts open. Fluid definitely was forced through the system, but never saw more than a few tiny bubbles. I followed up with a 30psi pressure bleed of both rears at the same time, followed by both fronts at the same time.

After all that, I'm still back where I started. I can't think of another possible bleeding procedure to try.

 

[victorofhavoc]

Wow.

Whats the condition of the bleed screws? Are they potentially crusty with old fluid and leaking some air back in when you close them? You do have at least an 8" hose hanging off the door bleed screw when bleeding?