Bleeding brakes problem

[bagpipingandy]

Hi all,

I just spent a day trying to get the brakes working on my 2001 A4 2.0 ALT, the job was to change discs and pads (simple right!!:(), it started off my wife complaining the front passanger brakes were smoking hot, I knew the pads were well worn well beyond the wear limit and I thought it could probably have a sticking caliper or pad and so had pencilled in new discs and pads and a good service at the calipers, so today I gets in about it and on removing the pads and disc on passanger side I thought it strange when pumping the pedal the piston would only come so far out and stop then the brake pedal went all soft with no feel to it, I never twigged and assumed soething simple like the piston was stuck and so carried on stripping the caliper removing it from the car, pinching the brake hose to prevent loosing too much fluid, any way all back together put the gunson ezibleed on it and nothing!! no fluid out of it at all, not even air moving, just nothing?? a very, very long time later and fluid moved every which way but down through the resevoir I need you help, basically on the front right I can use the ezibleed (only just with 25PSI!!) but the passanger side nothing,

surely it should be as simple as apply the pressure kit to the brake resevoir with max 20PSI and open bleed nipples in correct order!!:aargh4:

I can bleed manually pressing the pedal down while someone on a spanner at the bleed nipple but the front passanger side does not drop the resevoir fluid level and eventually runs out of fluid, the drivers side front I can bleed in the same way but at least the resevoir drops???

I never seen this before, my only conclusion points to the master cylinder faulty, would any one agree does this point to the master cylinder or some thing else?
ive never had to change one before so want to make sure before i buy anything

all thoughts and ideas welcomed

Andy

[RuslanA4]

Hi. I've bled brakes on all 4 on my A4 (same as your one) without any problem. I've done it the old way of pumping the pedal and opening bleed valves. Also I have had an engine running so the abs pump would work ( me dad told me to do so years ago when teaching me how to fix cars). Also, A4's of that year suffered vacuum booster water damage, which could lead to number of problems with brakes. I would suggest to change both vacuum booster and master cylinder together and then do the bleeding.
Hope this helps

[Doctle Odd]

Did you let it run out of fluid at any point? You might need to cycle the ABS pump using VCDS

[bagpipingandy]

No definetely didnt loose much, had clamped the hose and removed the caliper so I "planned" to loose none, then just bleed the empty caliper but it never turned out that way!!, I never lost any though as there was no signs of fluid anywhere, I did check though as at one point I thought I was going mad!!, the problem seems to be I cant get fluid from the resovoir into the master cylinder as strange as it sounds, I could actually bleed fluid up the way from the caliper bleed nipple through abs and to the Line 1 right at the master cylinder but not down the way through the resevoir which should be page 1 bleeding stuff!!

thanks for the replies,

Andy

[Doctle Odd]

Take a look at your reservoir see if it cracked at the seam, will it allow fluid out using gravity? It could be the master, you say the pedal went soft but did it firm up again after bleeding?

[bagpipingandy]

No the pedal is useless no feeling what so ever

[OddBallBoy]

According to a post by Crasher on another thread a couple of weeks back, you should never clamp VAG hoses as (I think this is what he said) they are braided beneath the rubber coating and will not open up afterwards. If you clamped one a little tighter than the other, would explain why you're struggling to get any out of one and only a bit out of the other. Might be worth loosening the flexi at the car end, see if you get any fluid out there - if so, replace hoses.

[bagpipingandy]

yes I did think perhaps it had collapsed but I tested it and i can push fluid extremely easy from the caliper up past the rubber hose out the top, even tried through the abs and up to the brake line going into the master cylinder it clear all the way ok, I can also pass fluid down through the system pressing the brake pedal and spanner method but no fluid is being replaced from the resevoir, it stays full and then after 4th or 5th up and down of the pedal the front left line runs out of fluid, my thinking is the master cylinder is faulty and for some reason not accepting fluid from the resevoir?? is this possible!??

regards

andy

[Doctle Odd]

OK first check the plastic ball joint socket at the pedal there's an outside chance it has became detached. If it's all in one piece you'll have to take the master off and check it. Once the master is off it's better to do a fluid change. Is the hose leaking above where you clamped it? open the joint above where you clamped the hose and see if any fluid comes out when you pump

[OddBallBoy]

Have never had the misfortune to suffer a problem with a master cylinder so cannot help on that I'm afraid, though I think I have heard of master cylinder piston seals sometimes inverting if you push the caliper piston back without opening the bleed nipple - I gather you should ALWAYS open the bleed nipple when you push the piston back.

You mention you can push fluid back through the brake flexi pipes from the caliper - is it possible that the lining of those flexi pipes might have become detached which would allow fluid to flow in one direction but not the other? For the cost of flexi pipes (less than £10 each if pattern), I would be tempted to replace those before I did anything else then try bleeding again.

[bagpipingandy]

Fluid runs ok both ways through the flexi hose, I opened the union at each end and pushed fluid both ways ok, i did have the bleed nipple open when pushing the piston in I find it best to get rid of the excess fluid this way and not push dirt back in the system, but the bleeding problem was more apparent when trying to pressure bleed the system, with no fluid being forced through at all, the pedal pushes fluid ok but no fluid is taken or used from the resevoir. I will strip the master cylinder off and see if the seals look like the issue, or i may just have to change it and saee what happens, i have also heard of the seals causing issues.

Andy

[Doctle Odd]

Have you access to VCDS?

[OddBallBoy]

Sorry mate, no more ideas for you, sounds like you went about things the right way so I'm stumped. Hopefully you can get a code read and that might help identify if it's to do with ABS unit, and if not, maybe master cylinder as you suspect. Best of luck...

[bagpipingandy]

Have you access to VCDS?

Yes full VCDS, scanned and no faults, Its got to be the master cylinder........ right!! :)

many thanks for the replies

Andy

[zollaf]

i had a similar problem the other day on the rear of something i had just put new brake pipes on. then i took the clamp off the pipe and all was ok :)
anyway, what can you see in the resevoir, any black crud. sounds like the mc isn't taking fluid so its either dragged something down into an inlet port so no fluid can get into the mc, or indeed the mc could be kaput. does the pedal come all the way back up though, as if not that will keep the inlet valve closed and not let fluid in. i would just try lifting the pedal to make sure its not jamming.

[Doctle Odd]

I was going to say use VCDS to cycle the ABS pump see if it's blocked but Z is closer to the mark

[bagpipingandy]

i had a similar problem the other day on the rear of something i had just put new brake pipes on. then i took the clamp off the pipe and all was ok :)


HA Ha i wish it was that easy, (i did check again!!! :)) Pedal ok and pulled up always pumped ok and connected still to ball rod.

so tonight master cylinder removed and clamped in the vice, pressure bleeder on it at 30PSI and fluid/air comes out one of the outlets and nothing out other, stripped the piston/s out of it and notice the extremely small filling valve on the 1st circuit barely opening, blew air back and forth and then could hear air flowing when it was opened, back together and pressure bleeder on it and then got air from both lines although only a small amount from the original "blocked line",

also on the car with no master cylinder fitted (pipes off) open both front caliper bleed nipples and fluid drips/runs out ok, I'm happier now to order a master cylinder as it may point to this valve not letting fluid in and barely opening, I THINK!! :)

wil give you an update with the new master cylinder

Andy

[bagpipingandy]

New master cylinder fitted and all working as it should :o, fluid finally flows from resovoir into master cylinder!!!

Regards

Andy

[OddBallBoy]

A shame you had to get new MC but pleased for you it's sorted😊

[bagpipingandy]

A shame you had to get new MC but pleased for you it's sorted

I got it from ECP who are offering a 30% discount online just now so all in it only cost £45 (not too bad) and it is an original OEM part manufactured by TRW which is exactly the same as the one I removed :), so happy with that, :)

Brakes also feel good too which is a bonus!! ;)

regards

Andy

[adamss24]

Don't we love a happy ending ?

[dufrais]

i think a pressure bleeder is so much easier in this situation?

[Doctle Odd]

You need to cycle the abs pump with VCDS

[dufrais]

no this is not needed unless the pump has been replaced

[Doctle Odd]

You're wrong mate

[dufrais]

ok maybe you can ring or text VW in the morning and confirm for me ;)

[Doctle Odd]

You can't rationalise with stupidity

[dufrais]

LOL Snap! :o