sinking brake pedal

[Outback 1]

As the title says a big thanks to Mr whippy. For his help on Sunday. After bleeding the system with the nanocom we now still have the abs light on and have a good pedal until we start the engine at which time it starts sinking to the floor! .can anyone give me some idea of what may be causing this thanks. Ken

[Outback 1]

anyone have any ideas:confused:

[schuy1]

By "sinking to the floor" do you lose all braking? If after it does this can you restore pedal by pumping?If so does it then remain hard? Or as soon as you remove pressure it recommences its U-Boot impression? Do you have braking at all? without engine assistance?

Cheers Scott

[Outback 1]

without the engine running pedal is great the problem only occurs with power assistance if you pump it it still does the same thing

[schuy1]

Do you have braking when you have good pedal? without engine assist it will be harder but does it stop u? Have you had some1 observe the fluid behavior in the reservoir when you pump the pedal? with and without the engine running? If you have fluid movement of any sort in the reservoir you have faulty valving in the cylinder. A faulty booster is just nothing at all in the way of assit. I can think of no real reason why it is doing that.
Cheers Scott

[Distortion]

If you pump the peddle does it stiffen up then go soft again if you hold it down.

I recently had a similar issues and it was a case of the fluid getting past the valve in the master cyclinder

[Outback 1]

yep that appears to be the issue tried a different booster on it today no difference so it must be bypassing inside the master cyl when vacuum assisted

[northiam]

If not the master cylinder?
The ABS modulator faulty bleeding internaly.
ABS modulator pump running.
Does the brake pedal drop only with engine running or ignition on?
ABS ecu faulty unplug modulator wiring harness at modulator.
Vac pump or manifold vac?

Regards

[twr7cx]

I had this and found two causes - master cylinder was faulty internally and a leaking bleed nipple on my front right caliper. Replaced both and brakes are perfect now.

[Outback 1]

installed a brand new master cyl and it is still doing it so tomorrow it will be a full manual bleed/fluid change and see how that goes :confused::censored:without the engine running perfect pedal

[LandyAndy]

installed a brand new master cyl and it is still doing it so tomorrow it will be a full manual bleed/fluid change and see how that goes :confused::censored:without the engine running perfect pedal

Are you aware you can use the ABS pump to pressure bleed the system??? Nanocom makes it easy,there have been posts on AULRO on how to jump a relay to make the pump run;);););););)
Im sure you will find the heads up with a search.
Goodluck
Andrew

[OffTrack]

Before you do the manual bleed try giving the modulator a work out with HDC. You don't need any hills, just put TC into low range, turn on HDC, then take it up to 40kph and lift off the throttle, and let the HDC brake you down to 7kph, then repeat 4-5 times. That should work any air trapped in the modulator internals into the main brake pipes where you can bleed out as normal.

[OffTrack]

Are you aware you can use the ABS pump to pressure bleed the system??? Nanocom makes it easy,there have been posts on AULRO on how to jump a relay to make the pump run;);););););)
Im sure you will find the heads up with a search.
Goodluck
Andrew

The Wabco bleed procedure (and from what I've been able to find the testbook bleed also) alternates between modulator bleed which operates inlet and outlet valves plus abs pump and running the ABS pump alone. The sequence is repeated 5 times before doing a manual bleed on each wheel.

Running the pump without the modulator bleed just saves having someone to pump the pedal for a manual bleed.

cheers
Paul

[Outback 1]

Are you aware you can use the ABS pump to pressure bleed the system??? Nanocom makes it easy,there have been posts on AULRO on how to jump a relay to make the pump run;);););););)
Im sure you will find the heads up with a search.
Goodluck
Andrew

Mr Whippy and i bled it with the nanocom last week this problem did not show up until after we had finished so now i will try a full fluid change and a manual bleed as there must be air trapped in the system somewhere :confused:

[PhilipA]

Just wondering what the problem was in the end or if in fact there was a problem.
I just did a bleed on my 2002 using a Nanocom bleed on each wheel 5 times using the Wabco procedure.
I then pressure bled the system using a pressure reservoir pump at about 7PSI. This always gives an excellent result on any car I have done.
The pedal is rock hard with engine off.
When the engine is started the pedal sloowly sinks about half way before it firms under heavy foot pressure.
However the actual braking and pedal feel are excellent and the brakes bite very high in the pedal travel and stop excellently.
To see if it made a difference I then went down a steep hill using HDC, but no difference.
Having a look at the Google entries , it seems that this behavior may be normal , but I don't know and it may have been doing it before , but I am now sensitised.
What are other's experiences.
Regards Philip A

[trev]

the brake pedal does fall away on startup to about halfway.
This seems to be the case for normal operation.

Trev.

[rangieman]

Just wondering what the problem was in the end or if in fact there was a problem.
I just did a bleed on my 2002 using a Nanocom bleed on each wheel 5 times using the Wabco procedure.
I then pressure bled the system using a pressure reservoir pump at about 7PSI. This always gives an excellent result on any car I have done.
The pedal is rock hard with engine off.
When the engine is started the pedal sloowly sinks about half way before it firms under heavy foot pressure.
However the actual braking and pedal feel are excellent and the brakes bite very high in the pedal travel and stop excellently.
To see if it made a difference I then went down a steep hill using HDC, but no difference.
Having a look at the Google entries , it seems that this behavior may be normal , but I don't know and it may have been doing it before , but I am now sensitised.
What are other's experiences.
Regards Philip A
I think Outback would be too embarassed to reply ;) He found it was normal:angel:

[Pedro_The_Swift]

The D2 does have a soft feel pedal,,
it can feel very bad if you jump out of a D1(who welded up the pedal?).

[timdo1]

Ive had the same problem after a long period of inactivity. Air trapped in system. I just used the car and it self bleeds air out. All fine after a good drive although when you first drive down the street be carefull because you dont have much in the way of brakes. Also once had a leak between the master cylinder and reservoir. Fluid was coming out over time and then air got in. I think youll find that the system self bleeds.

Good luck and be careful.

[ballbag]

Identical experience for me, PhillipA. I've had ABS unit out twice, master cylinder out once, calipers off once, bled the system at the ABS module and at the bleed nipples as per RAVE and Wabco multiple times each,.... pedal travel is still a long stroke. I have a motorbike that is similar and the common 'fix' for it is to swap it out with a different model master cylinder. No fluid loss so I just accept it as English charm.

[wrinklearthur]

The difference in operation is definitly noticeable from the soft feeling pedal that our D1 had before, to the pedal now not stopping at a halfway point and slowly sinking further towards the floor.
There is no fluid loss so I can assume that the brake fluid is finding it's way from one circuit into another, past a worn seal somewhere, --- but where?

I now have another master cylinder to try and i will see what difference that makes, a process of fault finding by substitution of parts.
.

[schuy1]

I think the "soft" pedal feel on a D2 is part of the "Chauffeur stop" system that the advertising blurb touted. Step on it as per normal and its a gentle slowing as per a chauffeur driven car so as not to upset the VIP's :D However if you step firmly(read here white knuckle moment as granma's mobility scooter charges off the shopping center footpath!) on the pedal it will harden up and bring the ABS into play quite quickly.
Cheers Scott

[Pedro_The_Swift]

must be said,,
I find the soft feel D2 pedal a godsend when towing the caravan,,:cool:

and as I've said before,, the D2 stops a whole lot better/faster than a D1.
pedal travel/feel regardless.

[Outback 1]

I think Outback would be too embarassed to reply ;) He found it was normal:angel:

like most people we become used to the extremely effective systems on our vehicles .as this is my first d2 however after many litres of fluid and several attempts at bleeding I could not get any air coming out of the system but still had a sinking pedal when you applied hard pressure so as a last effort I took it to a dealer who was previously the nearest lr dealer they bled it and could get no air either and stated it was working normally when you brake normally it stops brilliantly , but if you exert heavy pressure you can still feel it sink hope this helps everyone out if not give me a call or pm cheers ken