Help Please So i hear a "Crack"

[DocEllis]

Ill try to keep it simple.. I was driving on the highway at a fairly low speed during traffic. So a lot of stop and go.. Then i hear this "CRACK" from the front passenger wheel and my pedal goes straight to the floor. I was able to pump pressure back into them to limp it to the dealership. But the whole time the pedal would goto the floor, rather smoothly. I took it in, and i was ASSURED nothing was wrong, however, after getting it back, the wheel began to heat up on drives to the point where i could litrally smell the tire (or some other rubber) beginning to cook. Rim was hot to the touch, and on flir it lit up like a christmas tree.. It does not do this immediately, only after a 30-40min drive does the clunking, pedal sink and poor braking occur. Im guessing now, but Id say that piston had cracked. I dropped it off again monday to HOPEFULLY have it rectified. But if they dont find anything wrong, again. Is there anything else that could be creating this under these circumstances? Any advice appreciated. Thank you.

 

[northpole]

the brake caliper seems to have a problem this is why the wheel got hot, they should find that the brake pad on that wheel has glazed over because of the heat and possibly find the brake disk warped. so i'd expect them to replace the front calipers, front brake disks and the front brake pads. that would be the only proper solution. Sure they could repair the offending caliper and fit new brake pads if the brake disk isn't warped, it'll be cheaper as less parts will need replacing.

 

[DocEllis]

The dealership finally dealt with it. It started with a bad flexline they refused to look at then proceeded to change just the caliper and not the rotor.. (sorta makes me sketchy about the REST of the car.. but so far so good?) then the warpage on the rotor grenaded the piston on the caliper since it wouldnt retract due to the flex line.. so they finally did the 3. The bearing thankfully didnt bake itself, but ill be taking a deeper dive into the rest of the car, knowing thats probably not the only place they tried to save a few bucks... Next stop, check engine light...

 

[DocEllis]

Ok so the check engine light was a nothingburger "Turbo underboost".. turns out my air filter was the culprit there. However.. Ive since had to replace both front calipers & rotors AGAIN, due to the dealership not actually doing things right in the first place.. thats a seperate headache i need to undertake on my own. but the question im getting to now. Is what kind of a nightmare is it to change the master cylinder & lines to the front on these things? I can find the cylinder just fine online. But what are the lines like on this? This car has to last me at least another 5-7 years, so i will be doing a majority of "this kind of thing" myself from here-on. Ive worked AS a mechanic over the years, so im not new to this by any means, but If anyones had experience doing the front lines on one of these 2015 a4 quattros, i would appreciate any insight/ advice you could give. Thank you in advance.

 

[northpole]

I haven't done it myself ( but judging by the amount of mates that all of a sudden went to the b8 and b8.5 models) i'll soon be asked to either help or find the problem on their cars... And when i don't know how it's routed or what the job entails i use the my Elsawin electronic workshop manual that has everything covered. Now i now you probably don't have it but luckily for you i found a free online version just create a new user account and browse for free... i suggest you use either a chrome or firefox browser as they both will help translate russian to english automatically if you change the settings to do so ( saves you from selecting the page to than choose translate). Sure it has an annoying popup, that'll come around a few times just wait and cclick on continue when it's done, but it is up-to-date and covers all models. And the reason why i'm pointing you to it is you can drill down to your exact car setup so you won't get irrelevant information, and if you become a paying member you can simply use the VIN number and voila no need to drill down in the car selection. It's simple enough to use if you've worked with any database before. And you can print the lot out if you'd wanted to.. i use the page on my mobile, laptop or tablet when I'm looking up stuff and i'm not at home.

It beats getting half informed info, plus they point out all the tools needed to do the task, how long it'll take the official dealer garages to do it. Tip: take that time and double it if you lack the access to a bridge and the special tooling needed for the task. I found that without the use of certain garage tools you never get to do it that quick.

 

[DocEllis]

Thats amazing, Thank you! Im going to stick my head in it today and see if i can follow the line back to the cylinder. But now since the calipers & everything was replaced, i now have a brake pad warning light on. I know the shop did everything correctly, so im assuming its just a "oh no things are different" momment the cars computer is having. But the shop said their machine could not reset the code. and i will likely have to take it to audi and their proprietary equiptment to have done. I love the cascade effect on this car lol. fix one thing, get a couple more issues. Well, in this case i dont think ive gotten to the root issue (that passenger rotor is starting to heat up again). Ive just been throwing money at the symptoms.. Either way, im almost there, i hope... lol

 

[DocEllis]

ugh no.. It gets very very hot.. The online app is pretty decent. but now my issue is identifying & tracing the brake lines back to the master cylinder.. all of which on that side likeley need to be replaced thats not something i can aford to have done.. the goal now is to find a decent brake line diagram. i cant seem to pull one from the app tho. And would you know what these 2 lines are?

(edit) It seems everything else is good. i managed to calm down and trace the brake line. seems i was having some kind of momment that obscured OBVIOUS details.. But my next 2 suspects are the abs pump/ motor thingy and the master cylinder.. the other 3 wheels are fine.. this side just doesnt ant to retract. its not "stuck".. i can push it back with little effort.. i think its this abs thing, maybe?

 

[northpole]

Look like the fuel lines... the one that gets hot is the return line. I-d put a jubilee clip on that loose one because the last thing you want is that popping off.

 

[DocEllis]

So that loose plastic thing would be its disconnect sleeve tool? I want to push it in, but i think thats how you would take it off?

 

[northpole]

It should have a securing clip in it check it as I don't have a diesel to check it right now... it's Saturday, my mates are all out.

 

[DocEllis]

Im stuck in a sort of "cyclic redundancy check failure"... Im pretty sure ive isolated the issue to either the master cylinder and/ or? brake booster and/ or the abs control unit.. If the booster had a vaccum leak that would explain the sligth pedal sink, i think. But so would bad seals in the master cylinder.. but those 2 cant be the entire issue because only 1 wheel seems to be SERIOUSLY malfunctioning.. that points to the abs unit, but still doesnt explain my pedal sink with no fluid loss.. so im stuck trying to reason with myself if its the booster, master cyliner or both.. i would rather not have to replace both. but that elsewould be doing that?. but without doing a vaccum check on the booster, is there any other way to test this?

 

[northpole]

Might be air stuck in the ABS unit... i'd take the car to have the brakefluid replaced before doing anything else... yes i'd pay for it as when the ABS unit has air trapped to get it out the best way is to use one of those professional bleeding machines... VCDS does have an option for this too but it's way harder without a professional system as that can completly flush the brakesluid systerm without the need for using diagnostic bleeding for the ABS unit.

 

[DocEllis]

Well its been a while since the last update. Thecar is still doing the same thing. but now im left with a real puzzle.. the calipers, lines, master cylinder and ABS pump have all been thurroughly checked (and in the case of the master cylinder, calipers & flexlines all replaced). Its left me with an unusual kind of problem.. The pushrod on the booster and likely the brake pedal height is what im being led to. I have been trying to find info on how to adjust the pushrod in that booster (also thinking the booster itself is having internal issues), but nowhere on the entire internet can i find someone actually adjusting the rod in "this particular" style of booster. when i put the master cylinder in, there is QUITE a lot of compression, as was the old one coming off. It sort of "ejected itself" from the booster. Am i right to assume that this is adjusted OUT too far? can the brake pedal adjustment inside also be a cause or could have been the problem all along? Its such a simple thing, im almost too embarrased to ask.