Brake problem - need help

[SteveYem]

Yesterday I attempted to change out my rear brake pads. I used VCDS to retract the parking brake. At one point I made a mistake and hit "end lining mode" while the brake caliper was off, which resulted in the piston pushing all the way out. Not a huge deal, I did the "start lining change" function again to retract the parking brake, then I was able to push the piston back into the caliper- however, the resistance was very very high so I had to loosen the brake fluid reservoir cap to relieve the resistance. Once I did so, the piston pushed back into the caliper with ease.

I hit "end lining change" to re-engage the parking brake, then cycled the parking brake on and off and it worked fine. I pumped the brake pedal a few times (with the car off) and after a few pumps the pedal firmed up as expected. Then this morning I got in to drive to work, started the engine and noticed that the pedal was very soft and just about went to the floor. There was very little braking force. I took a slow drive around the block and the car would barely stop. I came home immediately and parked the car, and confirmed that the parking brake is working properly.

I confirmed that the brake fluid reservoir cap was secured tightly. I turned the car off and pumped the pedal a few times and it firmed up as expected.

Any ideas what could be happening? Is it air in the lines? Do I need to do something else with VCDS or some sequence of pumping the pedal to get my braking pressure back? Thanks in advance for any advice.


Edit- I never ended up changing the brake pads because after I hit the snag with accidentally fully extending the piston and figuring out how to push it back in, I ran out of day light and just put the original (OEM) pads back in.

[theswoleguy]

Sounds like air in the lines.

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[chaos2984]

umm. How come you changed the pads already? Did you just want to upgrade from stock? If you just put factory pads back on it for some reason just take it to the dealer and say it has a soft pedal and just play dumb about you messing with it. Or put the factory pads back on it and take it to the dealer.

But if you intend to fix it. Did the piston pop out of the caliper? If that did happen you got air in the system and it needs bled out. It sounds like you got air in the system somehow.

[anerbe]

Yup, sounds like you introduced a lot of air into the lines when the piston came out. Pushing back was obviously hard, because now there's additional air in the line. When you opened up the reservoir bottle, you pushed back up the air into the lines, displacing fluid back in the reservoir..

You need to bleed the brakes.

[TexasDfwS4]

Somethings never change from old school to new school. Air in the lines...

[SteveYem]

Thanks for the replies. I am also leaning toward air in the line.

[SteveYem]

umm. How come you changed the pads already? Did you just want to upgrade from stock? If you just put factory pads back on it for some reason just take it to the dealer and say it has a soft pedal and just play dumb about you messing with it. Or put the factory pads back on it and take it to the dealer.

But if you intend to fix it. Did the piston pop out of the caliper? If that did happen you got air in the system and it needs bled out. It sounds like you got air in the system somehow.

I wanted to install a set of Akebono pads to reduce brake dust. The OEM pads are back in (I ran out of time so I just put it back the way it was), but the pressure in the line is so low that I will not risk driving it to the dealer.

Yes, the piston appeared to have come out as far as it could go on its own. The dust boot around the piston was just about fully extended. At this point I am hoping to get into the local shop (less than a mile away) tomorrow morning to have the brakes bled.

[SteveYem]

EDIT - nevermind.

[SteveYem]

Alright guys, sorry to be a nudge about this, but I'm trying to learn as much as possible from my mistakes.

If the root issue is indeed air in the brake lines, then does it make sense that the pedal becomes very firm (i.e. barely any travel) when I pump the brake pedal a few times with the car turned OFF, yet there is barely any pressure in the line when the car is ON (i.e. engine running)?

Apparently I do not know enough about the inter workings of the brake system. What is it that changes within the hydraulic circuit that causes the change in brake line pressure when the car is started? One of the reasons I am asking is that all of the videos I watch for DIY brake bleeding say to gauge the success of the job by how the pedal feels. But since the car is turned off , I know the pedal will feel very firm (since that's how it feels now), so how will I really know when I've removed sufficient air from the line?

EDIT - One more question: Since I only manipulated one of the brake calipers (the driver side rear) to lead to this problem, can I just bleed the line from that caliper, or will I need to do all four?

[theswoleguy]

Steve

Eventually pumping the brakes 1-3x with the car off will lead to a solid feel. The reason the pedal is softer (regardless of air, if air just even softer) is the brake booster combined with vacuum from the engine gives brake assist. Thus is why when you go aftermarket cams you sometimes have to add a vacuum pump or live with stiff brakes. With that being said do one of the following:

1) motive power bleeder to bleed the brakes, start with the passenger rear, driver rear, passenger front, then driver front. you want to move from farthest to closest to the master cylinder

or

2) with a partner, pump the brakes till stiff and press and hold
crack bleeder screw
pedal will go to the floor (still holding)
tighten bleeder screw
pump brakes up again (going from very soft to hard)
crack bleeder screw again (check for air leaving the system)
repeat till no air bubbles come out
move to the next wheel (still following farthest to closest)

IF you are holding the brakes and crack the bleeder and you pump before he tightens it, you can siphon air back into the system.

[SteveYem]

Steve

Eventually pumping the brakes 1-3x with the car off will lead to a solid feel. The reason the pedal is softer (regardless of air, if air just even softer) is the brake booster combined with vacuum from the engine gives brake assist. Thus is why when you go aftermarket cams you sometimes have to add a vacuum pump or live with stiff brakes. With that being said do one of the following:

1) motive power bleeder to bleed the brakes, start with the passenger rear, driver rear, passenger front, then driver front. you want to move from farthest to closest to the master cylinder

or

2) with a partner, pump the brakes till stiff and press and hold
crack bleeder screw
pedal will go to the floor (still holding)
tighten bleeder screw
pump brakes up again (going from very soft to hard)
crack bleeder screw again (check for air leaving the system)
repeat till no air bubbles come out
move to the next wheel (still following farthest to closest)

IF you are holding the brakes and crack the bleeder and you pump before he tightens it, you can siphon air back into the system.

Thanks for the advice. I suppose that since all 4 calipers are connected to the same hydraulic circuit that I will need to bleed all four corners, yes?

Another thought I had was whether it is possible that the level in the reservoir dropped too much when the piston was all the way out, that it allowed air into the master cylinder when I took the reservoir cap off for relief to push the piston back in.

[theswoleguy]

Thanks for the advice. I suppose that since all 4 calipers are connected to the same hydraulic circuit that I will need to bleed all four corners, yes?

Another thought I had was whether it is possible that the level in the reservoir dropped too much when the piston was all the way out, that it allowed air into the master cylinder when I took the reservoir cap off for relief to push the piston back in.

if i bleed one i bleed them all, kind of a best practice thing for me. you lose a minute amount of fluid anyway.

[SteveYem]

A quick update, and to say 'thank you' to everyone that chimed in on this topic. I was able to drive the car to a local shop this morning (~1 mile away) and they bled the brakes which took care of the problem completely, as far as I can tell. He said the rear driver side (the one I was messing with) sputtered out a big slug of air while the other 3 corners had little to no air come out. He had to add a very small amount of fluid (Pentosin Super DOT4) to get the reservoir to the correct level.

Now that the problem seems to be taken care of, I want to write out what led me to this problem in the first place, so that hopefully nobody else as inexperienced as me will find themselves in the same predicament. Sorry in advance for wall of text:
I searched on the forum for a DIY on replacing the rear brake pads. A few of the threads I found contained links to the tutorial on the Ross-Tech website, so I followed the Ross-Tech instructions which detail all of the steps for disengaging and putting the electro-mechanical parking brake into the service position ("start lining change" mode if I remember correctly). When I got to the step in the Ross-Tech tutorial that says "Change brake pads", I removed the two bolts securing the caliper, removed the electrical and hydraulic lines from their brackets to give myself some slack to work with, and wiggled the caliper off the bracket.

Here is where I went astray and stupid/lazy. I was under the impression that putting the EPB in "lining change mode" would fully retract the piston so as to allow easy removal of the caliper from the bracket, and allow enough space within the caliper to allow assembly with the new (thicker) brake pads. When I was removing the caliper I noticed that it still took a little force to remove it, i.e the piston was still touching the back of the inner pad. I wiggled the caliper off of the pads and bracket, removed the existing pads and inserted the brand new replacements, and then of course when I tried to put the caliper back on the piston was too far out to fit behind the inner pad. I thought to myself "hmmm, I must not have properly disengaged the EPB because the piston is not retracted sufficiently into the caliper. I better cycle the EPB out of and back into lining change mode to get the piston fully retracted so I can install these new pads". THIS WAS ABSOLUTELY INCORRECT! Putting the EPB in lining change mode does NOT retract the piston itself, but it disengages the electro-mechanical parking brake device from the piston so that the piston can be manually compressed back into the caliper just like one would do for any conventional brake caliper. I know most people here would say this is obvious, but to me it was not. The combination of the Ross-Tech instructions saying simply "change the brake pads" and everyone saying "don't manually compress the piston because it will damage the emergency brake" led me to do what I did. I'm not blaming anyone but myself - I simply interpreted the instructions and warnings incorrectly, and clearly have no formal training on any of this.

So, getting back to it - the caliper was off of the bracket and I decided to cycle out of and back into lining change mode. Well, while the piston does not appear to physically retract when entering lining change mode, it sure seems to push out until it hits something when ending lining change mode. Since there was nothing in the caliper for the piston to hit, it just kept extending until it hit the end of its travel (I suppose). The dust boot was fully extended, and the piston must have been protruding ~2 inches out from the back of the caliper. Immediately I knew that was not a good situation, so I cycled back into the lining change mode and while I could hear the EPB mechanism disengaging, the piston did not retract at all. When I tried to compress the piston back into the caliper with a brake pad spreader tool, it would not budge. That is when I decided to open the cap of the brake fluid reservoir, at which point the piston pushed back into the caliper with ease.

We are still trying to figure out physically where the air entered the line. Presumably it occurred when the piston was fully pushed out of the caliper, so the immediate thought was that the piston came out far enough to allow an air gap between the piston and seal, thus allowing air into the line; however, I checked very closely for any leaking brake fluid and was unable to find any. The tech at the shop this morning agreed that there was no apparent leaking brake fluid. He thinks that possibly there could be some between the piston and the dust boot, but boot creates a good enough seal to contain it.

What I learned:
1) I'm not qualified to do various routine maintenance items on this car
2) Once the EPB is put into lining change mode via VCDS, the caliper is just like any other floating brake caliper I have encountered, meaning the piston can be (and must be) compressed manually to allow installation of thicker brake pads
3) How to bleed my brakes at home (although I ultimately had the shop do it for me this time)

[theswoleguy]

Awesome glad you got it sorted out. Depending the age on the fluid it's recommended roughly every 2 years or more frequent if you track.

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[14S4GWM]

If you keep doing these things on your own and learning from all your mistakes you'll be qualified soon enough.

[SteveYem]

Awesome glad you got it sorted out. Depending the age on the fluid it's recommended roughly every 2 years or more frequent if you track.

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Thanks again, I appreciate your help on this! I would have bled them myself if I hadn't been up against time/lack of daylight constraints, not to mention having to do the work in my driveway in cold ambient temperatures. But I'm going to make up a DIY bleeder apparatus (clear tube, bottle with holes in cap, etc) so that I am ready to go for the next routine maintenance.

If you keep doing these things on your own and learning from all your mistakes you'll be qualified soon enough.

LOL I was thinking the same thing! I never did this stuff as a kid/teenager and didn't really get interested until recently, so I figure I'm making a lot of the mistakes and learning lessons the hard way that someone would typically make when they are much younger. I am one of those people with an engineering degree but not much hands-on experience, so all of these DIY attempts are an effort to make myself more well-rounded and get an appreciation for the challenges that the field guys encounter on a daily basis.

[14S4GWM]

^ There is nothing wrong with learning. It will save you time and money if done right. So far between the oil and brakes you're not doing to bad. Both being maintenance things you will do again consider yourself good. The front pads are easier. I changed to Akebono and love the no dust feature. Keep in mind these cars are over engineered so don't over think it like I know you want to being an engineer. This is my first Audi and there is definitely a learning curve. Keep trying man.

[SteveYem]

^ There is nothing wrong with learning. It will save you time and money if done right. So far between the oil and brakes you're not doing to bad. Both being maintenance things you will do again consider yourself good. The front pads are easier. I changed to Akebono and love the no dust feature. Keep in mind these cars are over engineered so don't over think it like I know you want to being an engineer. This is my first Audi and there is definitely a learning curve. Keep trying man.

Thanks for the kind words. I won't give up....it's way too much fun pretending to know how to turn a wrench! I've replaced brake pads and rotors on previous cars but all of the cautioning regarding the parking brake on this car threw me for a loop. In fact I swapped the front pads to low-dust ones on this car and the job was very easy and routine, once I figured out how to work that damn spring clip.

[14S4GWM]

That spring clamp got me. I chipped my caliper, was so pissed.

[SteveYem]

That spring clamp got me. I chipped my caliper, was so pissed.

Yep! So actually, I had to do the front brake job twice because the first time I used anti-squeal grease on the backs of the new pads, resulting in rattling/clanking sounds every time I hit a bump. @drob23 recommended that I use the red CRC Brake Disc Quiet goop which hardens up a bit to act more as an adhesive than a lubricant (similar to the way the OEM pads are glued in place), so I took the pads back out, cleaned the backs and reinstalled using the CRC stuff. To your point - the first time I did the job I was extra careful with the clips and was able to remove and reinstall them with no collateral damage. The second time around I guess I got cocky and was not as careful, resulting in one of them slipping out when it was loaded up and taking a nice little chunk out of my black caliper paint. And not to mention accidentally getting some brake parts cleaner on the S4 logo on the caliper, resulting in a now faded and slightly smeared S4 logo. FML haha

[14S4GWM]

It's always something lol. As for the S4 logo on the caliper I saw guys on here sanding them down lightly to bring a better silver color out and you can buy the logos on ebay. Stick the logo on and clear coat with hight temp clear and they look better then factory. Those silver pieces pop out of the caliper easy. I have everything to do it just haven't gotten around to it.

[jsh139]

If you keep doing these things on your own and learning from all your mistakes you'll be qualified soon enough.

This. Learning from your mistakes is how you get better. I once cross-threaded a bolt in the AVCS oil feed line in my Subaru STI. I started the car and oil POURED out all over the engine and on my garage floor. Huge mess. I had to have Subaru roadside tow me to the dealer and they had to put a helicoil in there because the threads were trashed. Learned my lesson. Always hand-tighten FIRST and stop wrenching when there's any resistance. Don't force it.

Anyway, don't be so hard on yourself :)

[GeoJoe]

I've used the Carista dongle and app to swap out the rear pads several times now. Easy stuff. No confusion on when the e brake is open or closed. Use of a $10 caliper tool helps get the piston back into place.

Also, don't make your own bleeder. Buy this. It's like a simple bug sprayer, no other tools needed. Attach it, pump it up to 20psi, open the bleeder screws and use the reservoir bottle to catch the old stuff. Easy, cheap and gratifying..

https://www.ecstuning.com/News/Motiv...ing_Products_/