I have been trying to rectify a problem with the brakes on my Octavia TDi, this is that whatever is done or changed there is no pedal it just falls away when pressed.

There is a momentary pause when the brakes are first applied and the power of the barkes is fine but then the pedal drops as though the master cylinder has leaking seals.

I have replaced the master cylinder and we have tested it blanked off from the rest of the braking system and the pedal is very good, as soon as the rest of the system is reconnected the pedal goes soft again.

The whole braking sytem has been bled a number of times to see if it is air but this makes no difference and the ABS has been replaced but again no difference.

We have also run with the ABS disconnected to prevent any electrical problems from affecting the brakes but again no difference.

Both me and my mechananic friend have come to a standstill and i'm looking for any suggestions.

Have you tested the vacumn pump?

How have you been bleeding the brakes? In particular, have you used a pressure bleeder at under 1 bar, or a vacumn bleeder? Have you used VCDS to bleed the ABS block?

I would say it's a "procedure" issue when messing with the ABS. You'll need to hook up VCDS as Ken mentioned.

VCDS? never heard of it. Is it another OBD connection tool?

Is there a specific operation that is required when bleeding the ABS, this problem was the reason the ABS was changed in the first place when changing the master didn't work.

Ah found VCDS not sure what difference that would make, we bled the car using the old fasioned two man method as I'm not keen on pressure bleeders.

The servo is new and was installed at the dealers.

You need VCDS to run the pumps in the ABS system to get the air out of it whilst you are bleeing the brakes.

The pedal drops on my Octavia too if I leave my foot on it. I've had mine bled using VCDS and it didn't make any difference. However, I followed Ken's advice and pressed the pedal hard down, then applied the handbrake hard before releasing the footbrake. This adusts the rear calipers and made a big difference to the amount of pedal travel on mine.

I'd actually put money on the OP having air in the ABS block now.

The advice in Post #6 para 2 is specific to adjusting the handbrake and hence the free travel in the rear calipers using the automatic adjusters, and won't help get air out of the hydraulics.

I see, the ABS is acting as an air trap, I thought the pistons would be extended when not powered so would not affect the bleeding.

One last thing I suspect I forget to mention, when the system has been bled but without the engine (and servo) on there is at most 1/2" of travel in the pedal then its solid with no travel at all. As soon as the engine comes on pedals on the floor.

Is that likely to be air in the system?

Are all the brake pads free is the carriers,

When did the problem start and what has been replaced

Rear brake pads and disks 6 months old seemed free at time and got copper grease etc.

Front disks and pads new with copper grease etc, both calipers have some corrosion along edge pad runs along, one caliper mount on the damper leg was helicoiled due to thread damage.

brakes were bled 2 man method resulting in weak brakes 1/2 pedal travel some pedal dive.

master replaced bled using 2 man method, at this point the servo linkage was broken by a friend jumping up and down on the pedal, this then damaged the servo which was replaced at Progress Letchworth.

When car returned 1/2 pedal travel similar pedal dive.

Re-con ABS replaced original bled using 2 man method when engine off no pedal travel, with engine on pedal to floor.

Tried another ABS with same result

This is where I am now.

Have you heard of diesel creep? Have a look on the internet. It may shed some light on the situation for you.

did this problem ever get solved as i am having the the exact same problem at present.

changed front pads bled system with pressure bleed and now no pedal except when pumped

have ordered a vacumn pump because the outlet pipe seems loose and so wont be sealing properly, but even after sealing round the outlet pipe with silicone nothing changed..

i should state this is a 2004 octi tdi @191k miles

When I got air in mine, I gave up and got a dealer to bleed it through. Not a proud moment for me, but better than having an unwanted brake failure.

The exit from the vacuum pump allows the pipe to rotate (at least mine does that too).

thanks for the quick reply, should have asked first and saved the the money on the pump...

I may have dropped a clanger by pressure bleeding from my wheel @ 30psi and every one is saying on here no more than 10psi

so it may be a trip to the dealers for me too...!!! ABS BLOCK? didnt know I had one never mind how to bleed it...

You need VAGCOM/VCDS to bleed the brakes. Also don't forget to bleed the clutch part of the system too.

Where are you based? You might find someone local who is willing to offer a hand.

You need VAGCOM/VCDS to bleed the brakes. Also don't forget to bleed the clutch part of the system too.

Where are you based? You might find someone local who is willing to offer a hand.

I,m in newcastle upon tyne any assistance would be greatly appreciated..

Bleeding the clutch won't affect the brakes. Clutch is better left alone if working correctly, IMO. If you're having trouble with this, you may well regret messing with the clutch.

Have you bled the master cylinder?

And 7psi is sufficient pressure for brake bleeding. Over 9psi is not recommended.

Hi, yes bled the master cyl.. think ill try one more bleed threw and then off the dealers

can you test a master cylinder?

looking at past posts I wonder if the abs valve block is the problem... can you bleed them?

also can someone please tell me why i would need VAGCOM/VCDS to bleed brakes, do'es it allow you to open the valves?

Edited 15 May, 201313 yr by Gilaz

I believe that VCDS exercises the ABS unit, so that presumably it releases any air which might be trapped in it.... If that is the case, then I guess you would then have to bleed all 4 corners afterwards to fully release the air?

This is starting to sound expensive....peeeing down now so it'll have to wait unless i can clear a space in the garage..

thanks for the imput.

Keith

Ross-Tech's description of the procedure for bleeding ABS using VCDS is in the first link below. The second includes a detailed description posted by a member on the UK-MKIVS forum.

http://www.ross-tech.com/vag-com/cars/absbleeding.html

http://uk-mkivs.net/forums/p/427824/2927247.aspx

Quick update... After a further bleed through..old fashioned way... All is well.. loads of air still in system after 1st bleed...

I wonder if the pressure bleed @ 30psi actually trapped the air....?

Quick update... After a further bleed through..old fashioned way... All is well.. loads of air still in system after 1st bleed...

I wonder if the pressure bleed @ 30psi actually trapped the air....?

That was the point of some of the 2011 postings; pressure bleeding (certainly at 30PSI relative) forces air into the ABS control block, and once it's there it's trapped until you do a computer bleed.

or drive it lots and cycle the hell out of the ABS. Not recommended if it's really THAT bad...