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Braking problems/Essay - Help needed! Pleaseee

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3.4K views 24 replies 10 participants last post by  Piza TT  
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#1 ·
Hi again Guys

Am getting a pretty dodgy intermittent braking problem. mk1 8N3 180 tt quattro ARY engine.

Basically, sometimes just before coming to a stand still, there is a noticable 'farting'/grinding/croaking noise coming from seemingly the brake pedal itself (or just behind it). 99% of the time it has been at very low speed but recently I had to do an almost emergency stop doing 60+mph and honestly it felt like when the ABS is supposed to kick in - it just didn't. infact it almost felt like the calipers/pads 'let go' of the discs.. the opposite of what I would have expected. it was rather disconcerting to say the least. I have felt ABS kick in in other cars before, and I know that they do let go and grab the discs really quickly, but this just seemed to let go.

Now that I come to think of it I can't remember the ABS ever kicking in (in the same way that I have felt it in other cars in my TT (the distinctive juddery slip before stopping) but maybe i've never had to brake hard enough? (although im sure I have) Also I Can not seem to remember ever seeing the ABS Light flash (as i assume it does) when the ABS Kicks in, and ive had the car nearly 10 years :lol:

I did a scan with VCDS and I didn't get any errors, regardless I recently changed both ABS sensors, and alas, the problem is still there. When I changed the ABS Sensors despite cleaning up the hole very well they were kinda stiff to get in... the gap did seem to be more like 3mm to the ABS Ring than the 1mm that the audi manual says it should be.. however ive got no ABS Warning light to justify this as a potential problem.. and the grinding problem was there both before and after changing the ABS sensors anyway.

you COULD say it feels similar to having completely shot pads under foot - but not really as honestly it doesn't really sound like it. Metal on metal noise is quite distinctive I'm sure i'd recognize it. it its really more of a farting pressurey noise than a scraping. And its only JUST before you come to a stop, no noise at all from like 40mph down to 7 or 8mph. And i'm also quite sure its coming from somewhere 'internally' as opposed to at one of the wheels.

The pads and discs are brand new brembo's all around, the old ones were literally less than half worn anyway about 2yrs old... the problem was there before & after changing these so pretty sure I can rule them out.

A mechanic friend said perhaps it could be the servo - so I did a brake servo 'test' (as per TT Manual) Pumping the pedal, turning engine on, pedal lapses, engine off, pedal pumps hard again. So can I assume servo operating correctly?

I had a theory after (Bare with me :lol: ) that, as i believe my stem seals need doing (Oil cap shaking all over the place when loosened &intermittent/regular smoke problem especially at idle/in traffic), that perhaps rather than the intake pulling negative pressure at idle there was some kind of positive backpressure at the intake causing a loss of brake boost (perhaps). However once I took the vac hose off at the servo there was a ton of vac and engine even ran rough until I plugged the hose with my finger. I can assume that good vac = good brake boost too. Also i'm assuming the one way valves are all ok as there was plenty of vac at the furthest point from the intake. Pedal doesn't feel hard to press at all (Like it does with engine off being towed for instance) Although braking certainly does feel less 'sharp and snappy'' than it should for new pads and discs.

I should mention that I also bled the system using a one man kit, in the correct caliper order - there was minimal air in the system if any, and the fluid was noticeably old and yellowish but not too horrible looking (easy to see when the new transparent fluid was coming through too) although I also bled the clutch too and this brake fluid from this section was pretty dark & filthy to be fair but again, no air. Notably more dirty than the fluid coming from the calipers though. Clutch operates fine, i'd even say very well (also new clutch kit flywheel slave cylinder 2018)

So to recap i've changed all pads and discs, ABS Sensors, checked vac at servo, bled the whole system, fresh ESP brake fluid too. No fluid level is dropping and couldn't see any leaks from around the master cylinder. The book mentions pre-filling the master cylinder with its bleed nipples before bleeding the car if the system has run dry but to my knowledge its never dropped below the min mark..

I'm now thinking it could be the ABS Pump/Module that's failed? (Surely VCDS would pick something up) OR potentially an internal washer/seal in the master cylinder, so have ordered a repair kit for the master cylinder in the hope that this solves it. I also have a replacement master cylinder I guess I could try from a TT I scrapped. (Does kind of feel like trapped air farting from behind the brake pedal however i'm sure if this was the case some air would have been present when bleeding the system/Bleeding would have solved the problem)

Come to think of it - my brake light switch failed under the pedal about 4 months ago, I changed it for a new one from Audi and brake lights now work fine, but ill have a root around that area later just incase something is a miss, but i'm sure the problem was even there before it stopped working (if memory serves). Also I could be wrong but I think the ECU may have held the brake light switch error after I changed it and reset codes, although it didn't throw a warning light, which I thought was a bit odd, i'll check tonight and see if the error is still there - don't really wanna be pulling out the master cylinder or the ABS Pump without reason.

Long shot but could it be the wheel bearing? Can hear a slight humming from the drivers side when turning left... pretty sure its the bearing from new. I changed passenger side a few months ago (but no grinding noise then just the usual bearing hum) ....

Any help will be massively appreciated here. Apologies for the huge message but I have seen a few threads like this and the response is usually

''Fiver says its the pads''

Well, its not in this case! (If only it was) I'm not ruling out something with the hubs/wheels though.

Many thanks everyone

Stuart
 
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#2 ·
Also using VCDS I was able to see the 'brake pressure' levels from the two lines, they were both the same and I think (from memory) Showing some 56bar when I applied the brakes heavily, and 0 when i let off. Ill recheck tonight to make sure that number is correct.

Cheers

Stuart
 
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#4 ·
Yep - checked the abs rings when doing pads and discs - the passenger side was renewed when I did the passenger wheel bearing, can't remember exactly why.. i'm pretty sure the old one wasn't damaged. Do you think the aftermarket ring on passenger side could cause a problem?

The driver side bearing is definitely on the way out so will change the ring for a like for like from GSF when i change it so they're matching, although i'm sure I compared it to the old one I took off and it seemed the same.

I will inspect for futher damage to the rings though - but wouldn't this throw a warning light? or make ABS kick in unexpectedly?

Thanks for the suggestion though it could well be something to do with it.

Kind Regards

Stuart
 
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#5 ·
To be fair mate your post is a long old read and I haven't read the whole of it yet, but usually a dirty or cracked abs ring can manifest itself as triggering the abs at low speed when coming to a stop, my s4 does it intermittently, have you logged wheel speed when the fault occurs?

Obviously your description does sound like the ABS is being triggered at low speed, it won't throw a fault code up if it's getting the wrong message as it just assumed the wheel has locked up.
 
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#7 ·
The wheel speed sensor can be rather sensetive if it is disturbed and not put back in exactly the same position, the clearance to the ring is less than half a millie so it's worth checking by getting your head in there and spinning the wheel to see if everything is true and straight. Might be worthwhile to disconnect the sensor and see if you have the same problem when slowing down, I would think your issue is in the area of that replaced ring!

Stevie
 
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#8 ·
outdoor stevie said:
The wheel speed sensor can be rather sensetive if it is disturbed and not put back in exactly the same position, the clearance to the ring is less than half a millie so it's worth checking by getting your head in there and spinning the wheel to see if everything is true and straight. Might be worthwhile to disconnect the sensor and see if you have the same problem when slowing down, I would think your issue is in the area of that replaced ring!

Stevie
Click to expand...
…"clearance to the ring is less than half a millie". I recall it me 0.3mm Stevie
 
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#9 ·
I think 0.3mm rings a bell from the Manual, didn't get a chance to check over the weekend - I will start with abs Sesnors and rings, have a good look round. I'm quite sure the gap was more like 3mm than 0.3mm once installed although the old gap looked about the same before the problem started!

Thanks for your suggestions though ill keep you posted!

Cheers

Stuart
 
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#10 ·
Can I just ask - if the gap between ABS RING and sensor was too big, and this was causing the problem by triggering the ABS for no reason i.e. the car thinks the wheels are locked or traction is lost....

Would this operate the ABS? If So would there be a flashing of the ABS/ESP light on the dash?

If so, there is no flashing of ABS OR ESP at any time.. especially when the crunching/croaking noise is felt

Abs light DOES light up on ignition as normal so I can assume the bulb isn't missing/taken out

It really does feel like the problem is very close to the foot. Im still edging toward master cylinder seal i think.

Does anyone think its worth bleeding/filling the master cylinder? Can I do this without re-bleeding the whole system? This wasn't mentioned as part of the normal bleeding proceedure in the Haynes manual, it says to only fill it if it has run dry - which it hasn't so its a bit of a long shot, really does feel like farty air under the foot though.

Cheers

Stu
 
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#11 ·
essex stu said:
Can I just ask - if the gap between ABS RING and sensor was too big, and this was causing the problem by triggering the ABS for no reason i.e. the car thinks the wheels are locked or traction is lost....

Would this operate the ABS? If So would there be a flashing of the ABS/ESP light on the dash?

If so, there is no flashing of ABS OR ESP at any time.. especially when the crunching/croaking noise is felt

Abs light DOES light up on ignition as normal so I can assume the bulb isn't missing/taken out

It really does feel like the problem is very close to the foot. Im still edging toward master cylinder seal i think.

Does anyone think its worth bleeding/filling the master cylinder? Can I do this without re-bleeding the whole system? This wasn't mentioned as part of the normal bleeding proceedure in the Haynes manual, it says to only fill it if it has run dry - which it hasn't so its a bit of a long shot, really does feel like farty air under the foot though.

Cheers

Stu
Click to expand...
Most likely Stu.
I replaced a wheel-bearing, creating too large a gap; the EML light wouldn't go out either. After being pointed in the right direction, correcting gap be cleaning the locating hole nicely, I attained the correct gap, easily.

The EML will probably stay on a little while - mine did for about 100 yds apprx. then went out. I've not seen a warning since: where's the wood..? :)
 
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#12 ·
Cheers Rlszer, When you say EML do you mean specifically engine management light? or ABS Light?

I have done pads a few times, and the ABS light does stay on for a few hundred metres or so once i've disconnected the pad wear sensor and replaced with new pads - But it always goes off after a very breif drive, this time it did exactly the same, ABS and ESP on after changing pads but then a trip to the local shop they both went off. I've never had an EML when doing the brakes? i don't think?

I did notice that the ABS Sensors (new) were VERY difficult to get in. The old ones had to be semi broken out.. I mean they really weren't budging. I cleaned the holes very well with degreaser/cleaner/WD/ even using some very fine wet and dry, i even slightly sanded the sensor housing just to make it smoother to go in, it was a real struggle getting them in. This is how I noticed the slightly bigger gap.

These were GSF 'Standard' Option abs sensors... maybe I should get the 'premium' ones just to see if they are a better fit. Kind of annoying.

I get the ESP light flashing as normal when the ESP kicks in - i.e. when cornering hard, this all seems fine. Its only the ABS Light that I never seem to see.

I think i'm going to go to my mates field and make the abs kick in and just verify that the ABS actually flashes under load and the pump is working - i also heard something about this 'reviving/Bleeding' the ABS pump (on other cars)

It may have been stupid of me to not mention it as i totally forgot to be fair, but myself and a friend had a play around with VCDS before this problem arose and I think he may have started the 'ABS Pump bleed' process on VCDS... He said the pedal went hard then soft, at which point there was certainly some strange noise but VCDS kept freezing at the same point before the test could complete...(I think due to aftermarket cable as it later did it with other modules too, ''too many communications to continue'')

Im thinking if this started to enter a bleed sequence it could have thrown a seal out of the master cylinder/somewhere as the bleed points were all closed? Can someone enlighten me as to the symptoms this would cause if you attempt to bleed it without opening any nipples? (VCDS didn't work for long enough to say anything about opening bleed points, only something about pressing the pedal before it froze)

Again, many thanks for the help its massively appreciated!

Stuart
 
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#17 ·
I had a very similar problem, noise and almost like ABS kicking at low speed, pulling up to junctions etc.

It was the longitudinal/Yaw sensors on their way out.

I changed the one behind the steering column with one from a scrapper and repaired the one behind the glove box using the guide on the forum.

All good now. I definitely thought it was more an ABS/brake problem as that's how it manifests itself but it wasn't.
 
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#19 ·
Hi Wally /Temperal

I did have a good good look at the master cylinder, it has never been off but I have recently bled the system so I guess it may well be worth a quick bleed of it to just see if there is any air in there. My gut tells me it feels like air somewhere/internal seal of master cylinder gone but obv I could be wrong. I had a good good look and feel around for leaks, couldn't find any at all and fluid hasn't moved. I may just swap it for the spare M C I have from identical car.. I also had my master cylinder repair kit turn up so will whack off and do in the near future.

I have new 'premium' (lol) ABS Sensors for both sides (even though my new 'standard' ones have been on about 100 miles, i'm not happy with how they are sitting and how the replacements went in) and new wheel bearing for the drivers side so will fit these at the weekend Trying to do one job at a time to eliminate the problem so I know what it actually was!

Wally interestingly I had the longitudinal (behind glove box) go bad a few weeks ago. I tried the repair myself twice... after many burns with the soldering iron and many hours of very careful silicone picking later both times the warning light just stayed on and VCDS was giving stupid readings of 24m/s when stationary :lol:. Particularly annoying as I treble checked all of the pins and the board for damage/lose connections and it all looked fine. I hear the best solution is to change the 8 pin chip thingy sometimes when resoldering as they can go bad as opposed to just become unsoldered so perhaps this was the reason (and not my crappy soldering! he says in vain)

Anyway in the end I couldnt find a new chip thingy for it so I found a module repair company and got one for about ÂŁ30 I think, swapped it and the warning light went straight off so I assume this is good and i'm just useless at soldering haha.

I will have another look at these on VCDS just to check the readings from long/lat sensors.. Failing that I will go to my friends field and have a good rag of the ABS to see what actually happens when its highly needed, Failing that I will disconnect ABS sensors just to see if that makes any difference, Failing that i think ill swap the ABS sensors (Replacing drivers side hub and abs ring too as i already done the passenger a year or so ago). Failing that I will Bleed M C... and system again if required.. Failing that I will replace M C with scrappy one/repair mine. Failing that I will change the lat sensor.. Failing that ABS Pump/Module Failing that Its going in the nearest ditch at 70mph (ironically probably due to brake failure) :p :p :p

How the **** have I had this bas**** 10 years....

Again, apologies for the longness and thanks for all your help

Cheers

Stuart
 
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#21 ·
Hi Wally

Funnily enough I made a point of driving home yday with it turned off - but the problem remained! To be fair it only did it once or twice over a 10 mile drive but it still did it. I would think if the long/lat sensors were giving silly readings it would throw a MIL like before but i suppose they could be inaccurate but within tolderances. Haven't had a chance to recheck with VCDS yet will try a short trip whilst measuring the block later (Pretty sure I could only find measuring blocks for Long sensor not the LAT sensor. This could be due to my aftermarket cable which only works with version 17 of VCDS which I run.

Im getting a lot of communication errors and I don't seem to be able to view all of the blocks that I should and modules, do you think this is due to the aftermarket cable? Might be time to invest in the proper cable I reckon.

Cheers

Stu
 
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#23 ·
Guys, I have been searching high and low for an answer to my query but cannot find at all.

What is the correct air gap between rear abs sensor and reluctor ring?

The rear left is almost touching whilst the rear right is at least double the distance from the ring.

Its the rear right that is causing me trouble but cant seem to push the sensor in any further.

Anyone with any info please let me know
 
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#24 ·
Hi I’m having the same issue I changed all the rotors all the brakes all the sensors. I just replaced the ABS module and still getting it. only grinds at low speeds when I break. Feel a real bad grinding vibration on the brake pedal at low speeds help somebody. 🙏🏽🙏🏽
 
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