Brakes frustration after VCDS bleed, advice appreciated

Mightyleader

Mightyleader

Member
Morning all,
I'm really frustrated with the brakes on Diane right now, and would love some advice.
Recently, I had the callipers replaced on the front disks as they old ones were causing binding and the pistons were in a sad state.
I had the repair done by a competent local mobile mechanic and I'm more than happy with that work.
Only two issues remained:
  1. The pedal was soft
  2. I still have Brakes/ABS warning lights.
I'll describe the issues I now have from this. After some research on this lovely forum and others in the same VAG vehicle world, it seemed prudent to do a VCDS-driven brake bleed as many had reported it did wonders with soft pedals.
I got a lot of information from this page here on A2OC, which led me to these clear directions (reply #10) on what to expect from the process all of which gave me confidence to go ahead.
So I got bleed tubing with non-return valves as directed, got two 11mm ring spanners and took time to set everything up (up on axle stands, front wheels off etc...) I even thought of a novel way to make the bottles to catch the fluid stand up, see pics...

IMG_6019.jpg
IMG_6020.jpg


Running through the process in VCDS everything seemed to be fine and I saw little air bubbles in the tubing. I topped up the reservoir as the process went on so it never emptied and the bottles collected just under a litre of fluid as the directions said.
HOWEVER. At the end of the process, when VCDS told me the bleed is complete, the brake pedal felt like it had zero pressure behind it and gently pumping it for time made no difference. I put everything back together and did a gentle test moving forward and back on the drive and sure enough there is ZERO brakes applied.
I can only assume that the process caused a leak, pipe split or maybe even the master cylinder seals to go.

QUESTION 1: Is this a correct assumption (I can't see any leaks dropping down under the car) or is there something I have missed and can do to resolve?

Secondly I still have the ABS/Brake warning light so I ran VCDS again and got the following output, which is clearly not related to the hydraulic system. I have checked the cabling to the sensor, the sensor (as best I can, I mean it's there and doesn't look broken) and the fuse.

Code: 
Address 03: ABS Brakes       Labels: None
   Controller: 8Z0 907 379 D
   Component: ESP FRONT MK60      0101
   Coding: 0007175
   Shop #: WSC 00000
   VCID: 49E5B47460A1
2 Faults Found:
00668 -  Supply Voltage Terminal 30
            002 -  Lower Limit Exceeded - Intermittent
00285 -  ABS Wheel Speed Sensor; Front Right (G45)
            012 -  Electrical Fault in Circuit

QUESTION 2: Are there any common places to check for issues in the wiring?
 
Similar story here - https://www.a2oc.net/community/index.php?threads/weird-brake-problem.47433/post-454883

IF this is your problem, best guess is the brake bleeding process flushes debris into the ABS valve block causing a valve to stick. Sometimes carefully repeating the bleeding procedure several times may clear it.
The link also explains a good way of testing the master cylinder to eliminate the possibility of damaged seals

Cheers Spike
 
You did make sure that the brake pedal never went full travel while pressing it I hope. I always place a block of wood on the floor under the brake pedal to prevent the pedal travelling too far down when pressing it. In use the pedal only normally travels so far. When the pedal passes this point there is a chance the seals in the master cylinder get damaged. I suspect the master cylinder seals are now damaged. Have you also bled the rear brakes?

You could TRY a "normal bleed" on all four wheels and also the clutch. Remember to place something under the pedal then bleed in this order..

Left Rear, Right Rear, Left Front, Right Front and lastly clutch. Make sure you never open the nipples too much as they can draw air in past the threads.

I use a hand held vacuum pump to suck the fluid and air out making pressing the brake pedal redundant ( also use to suck fuel up to the tandem pump after replacing them. ) Others use pressure bleeders but more care and experience is needed when using those.

Whatever method used it is critical to ensure the reservoir is kept full with fresh brake fluid.

Good luck.
 
On the ABS fault. have you tried disconnecting the sensor and inspecting the pins for corrosion? A squirt with contact cleaner cannot go amiss. I suspect the wiring got nudged in the caliper swap.

Andy
 
Yes for the ABS fault, as Andy said. Also worth checking the wiring loom as it passes down the strut for damage caused by incorrect routing and tyre rub. I have seen these cables rubbed through and broken off in the past. Wrong wheel sizes ( width and offset ) greatly increase the chance of cable being damaged.
 
audifan said:
You did make sure that the brake pedal never went full travel while pressing it I hope. I always place a block of wood on the floor under the brake pedal to prevent the pedal travelling too far down when pressing it. In use the pedal only normally travels so far. When the pedal passes this point there is a chance the seals in the master cylinder get damaged. I suspect the master cylinder seals are now damaged. Have you also bled the rear brakes?

You could TRY a "normal bleed" on all four wheels and also the clutch. Remember to place something under the pedal then bleed in this order..

Left Rear, Right Rear, Left Front, Right Front and lastly clutch. Make sure you never open the nipples too much as they can draw air in past the threads.

I use a hand held vacuum pump to suck the fluid and air out making pressing the brake pedal redundant ( also use to suck fuel up to the tandem pump after replacing them. ) Others use pressure bleeders but more care and experience is needed when using those.

Whatever method used it is critical to ensure the reservoir is kept full with fresh brake fluid.

Good luck.
Click to expand...
I might give that a try. Can I do that with simple pipes and non-return valves in them? Also where is the clutch bleed?
 
audifan said:
Yes for the ABS fault, as Andy said. Also worth checking the wiring loom as it passes down the strut for damage caused by incorrect routing and tyre rub. I have seen these cables rubbed through and broken off in the past. Wrong wheel sizes ( width and offset ) greatly increase the chance of cable being damaged.
Click to expand...
Hey both, thank you will give it a good inspection. The pins look OK but will try with a squirt of contact cleaner. The ABS sensor issue predates the calliper swap but I will check the loom as you suggest.
 
Yes your same bottles set up can be used to "normal" bleed the brakes. Only do one at a time in the order I specified above and ensure the nipple is closed before moving on to the next one. Be careful to not slacken the nipples too much. With the tube you want to make sure there is an arc in it so the fluid travels up hill a little after the bleed valve, this will also catch air from the bleed nipple threads ( usually ). I do not use the one way valves as found some can cause problems, just make sure there is some brake fluid in the bottom of the bottle and that the end of the bleeder tube is immersed into the fluid - this stops air being drawn back into the system. Remember to restrict the downward travel on the brake pedal to save the master cylinder seals.

The clutch is very easy to bleed, but even greater care is needed with the bleed nipple as it is PLASTIC. The slave cylinder is located on the upper rear of the gearbox almost next to the selector cables. Audi only fitted the single fluid reservoir and that also supplies the clutch. Bleeds very easily and quickly using the tube and bottle method. The clutch pedal can safely be pressed all the way down. Be aware the pedal will very probably just sit at the bottom of its travel - do not panic and simply slowly raise the pedal back up using the side of your foot. 4-6 depressions of the pedal is more than enough for the clutch. Once the pedal has been raised for the last time and the nipple carefully torqued the pedal will now return as normal when you take your foot of the pedal. Again keep the reservoir full.

Once complete, top up as needed and clean down the reservoir of any spills after refitting the cap tightly. Clutch should now work as before or perhaps slightly bet and there should be a good brake pedal.

Here is a picture of a bleed tube ( marked A ) fitted onto the clutch slave bleed nipple...


1650905310576.png
 
Howey I covered pressure bleeding in an earlier post and why I do not recommend it unless you know exactly what you are doing.
 
audifan said:
Howey I covered pressure bleeding in an earlier post and why I do not recommend it unless you know exactly what you are doing.
Click to expand...
Cant see it that tbh
Its industry standard practice, if any individual feels uneasy about the procedure i would recommend they do not touch anything brake related.
 
Not going to get into an argument about pressure bleeding as that is not my intention, nor is it to have a "go" at you, but only mention the following points.

Unless you are experienced in using and preferably trained ( hence industry standard ) it is too easily to empty the reservoir with pressure bleeding.
The kit may be too expensive for the casual home mechanic as many use shop air from a compressor.
There is a possibility of a cobbled together kit being used that can easily over pressureise the system.
Have known of people forgetting to release the pressure before removing and the dangers that involves.

And yes I DO like pressure bleeders but have been around them for more years than I care to think - but I know exactly how to use them SAFELY.
I also agree that the person needs to have a required level of skill before they even contemplate touching the cars braking system.

This is why I SUGGEST the full manual bleed of pressing the pedal and collecting the spent fluid in a suitable container, my preferred version of vacuuming the fluid through with a hand held pump, or the VCDS ABS method.
 
@audifan in no way was i intending to become argumentative!

With a bit of common sense (strongly believe most A2 owners have this) and from about £40 pressure bleeding is perfectly safe and possible, not exceeding 20 psi and plenty of brake fluid in the container, theres very little to go wrong in my opinion.
In just one BFC (brake fluid change) the kit pays for itself and you know its been done and done correct (would not trust a garage to do a BFC seen far too many just tick the box and add ££ to the invoice, not cool)
We all have our own ways and good to have more than one solution!

Not tried myself but have heard making the abs opperate can solve problems, so a bit of rally driving on a stoney car park with intense braking can indeed help apparantly
 
Howey said:
[Not tried myself but have heard making the abs opperate can solve problems, so a bit of rally driving on a stoney car park with intense braking can indeed help apparantly
Click to expand...
That shoul be hard to achieve without any brakes ;).
Anyway, I did a full manual bleed a few months ago and for next time I will buy a pressure bleeder tool. Manual clutch bleeding was a pain in the back :).
 
Bleeding valve is down and you need to bow down and also opening/closing the bleeding valve is very uncomfortable due to its position and all other stuff around. Anyway, I could feel my back after this :).

@Mightyleader: here is my process if it is of any help:

@audifan: why do you start on the left rear? Don't you always start with the brake that is furthest away from the brake cylinder? Or do RHD cars have the brake cylinder and ABS pump on the right side?
 
Last edited:
audifan said:
You did make sure that the brake pedal never went full travel while pressing it I hope. I always place a block of wood on the floor under the brake pedal to prevent the pedal travelling too far down when pressing it. In use the pedal only normally travels so far. When the pedal passes this point there is a chance the seals in the master cylinder get damaged. I suspect the master cylinder seals are now damaged. Have you also bled the rear brakes?

You could TRY a "normal bleed" on all four wheels and also the clutch. Remember to place something under the pedal then bleed in this order..

Left Rear, Right Rear, Left Front, Right Front and lastly clutch. Make sure you never open the nipples too much as they can draw air in past the threads.

I use a hand held vacuum pump to suck the fluid and air out making pressing the brake pedal redundant ( also use to suck fuel up to the tandem pump after replacing them. ) Others use pressure bleeders but more care and experience is needed when using those.

Whatever method used it is critical to ensure the reservoir is kept full with fresh brake fluid.

Good luck.
Click to expand...
I can’t guarantee I didn’t push pedal completely every time while pumping however I was gentle.
 
mtl said:
Bleeding valve is down and you need to bow down and also opening/closing the bleeding valve is very uncomfortable due to its position and all other stuff around. Anyway, I could feel my back after this :).

@Mightyleader: here is my process if it is of any help:

@audifan: why do you start on the left rear? Don't you always start with the brake that is furthest away from the brake cylinder? Or do RHD cars have the brake cylinder and ABS pump on the right side?
Click to expand...
Thank you @mtl I’ll watch and learn.
@audifan I’ll give it a try bleeding my system then. I have drum brakes on the rear, whereabouts are the bleed valves? I can’t seem to find them.
 
On rear drums the nipples are next to where the rigid metal brake pipe enters the backing plate. These nipples tend to get badly rusted so lots of penetrating fluid then be gentle.
 
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