Hi guys just fitted new front hoses and bled the system through with gap tool and now the pedal is firm if you pump it but then it goes to the floor, so not sure what is going on here
If it was air surely it would be spongy but it’s not just goes to the floor, possibly master cylinder seals?
Was ok before but I guess they could fail ,any thoughts welcome 1990 3.5 v8 defender
2000 4.6 v8 30th anniversary prins lpg
2004 4.4 v8 vogue prins lpg
2011 4.4 TDV8 Vogue
faultmate extreme
rsw allcoms
Autel 906BT
Gap iiD tool

I have the same thing and am working through it now. My pedal sinks, but it is very slow. I’ve tested emergency braking and also numerous braking events in quick succession and I’ve never had any issue in slowing quickly and when needed. Braking force is good. However, if you sit with foot on brake pedal and continue to press then yes, it does slowly sink. I’m pretty certain this should not happen and a fully ‘sealed’ system should not do this and result in a firm but not sinking pedal with constant pressure applied.

I’m pretty certain that I have a small leak somewhere. I monitor brake reservoir levels and I can’t see any obvious drop but can only continue to monitor over time to see.

I had problems with front bleed nipples (Brembo 6-pot) weeping after I did a full brake flush about 3 months ago. The screws were close to seizing so after carefully cracking them off, I then had to tighten them much more than I was happy with to stop this. I tried replacing them with new over the weekend as a fix. However, this has been one of those ‘open a small can of worms’ events as the new bleed screws just would not seat correctly so now my problem is worse than when I started. I think they are cross threading due to corrosion in the threads. I also had to reinstall a couple of the old screws as was struggling to get the new ones to thread in. I’m certain the new screw were correct spec: M10 with a 1mm thread pitch.

My next step is to do a front brake caliper rebuild to try and sort this. I have new piston seals, dust boots and more new nipples so I plan to take both fronts apart this weekend, clean and rebuild. Whilst I’m at it I am going to use a tap to carefully re-thread the bleed holes before fitting new screws. I’m hoping this will rule out problems with front and stop pedal sink. If not, I’ll also rebuild the rears, which I think are beginning to bind so need it done anyway. If after that there’s still pedal sink, the only option is to start working up the lines, checking rubber hoses, metal pipes and their connections as far as master cylinder.

It would be great to hear your progress and plans troubleshooting this yourself!

Also would be great to hear from anyone regarding sinking pedals. Obviously if pedal goes to floor quickly that is bad, but is it possible for a pedal to sink only very slowly and this to not be an issue? Andy

2010 4.4TDV8 Vogue SE in Santorini Black with Ivory interior
2017 Audi SQ5 3.0 V6T Quattro in Volcano Red
2001 Audi Allroad 2.5 TDI manual with low-range in Highland Green. Currently SORN whilst undergoing some serious restoration!

If there is no fluid loss would that point to the master cylinder leaking internally? 2012 tdv8 Westminster arrived Jan 19 gone Dec 23

200 TDi discovery bobtail gone
RR classic v8 bobtail gone
300 tdi Discovery 3 dr gone

master brake cylinders are a known fault and they are not in stock much.

Well I guess I’m not on my own with this , I must of bled the brakes now 7-8 times using the gap tool and engine running, the pedal is lovely and firm with engine off but when you start it it’s firm then slowly sinks which can’t be right.
I’ve had a pressure bleeder feeding the mast cylinder and using the gap tool as well, I changed the master cylinder for a used one but still the same, maybe both master cylinders have failed. No fluid loss or leaks anywhere. If I knew it was the master cylinder I would buy a new one ,Not sure what else to try 😤😤🤔 1990 3.5 v8 defender
2000 4.6 v8 30th anniversary prins lpg
2004 4.4 v8 vogue prins lpg
2011 4.4 TDV8 Vogue
faultmate extreme
rsw allcoms
Autel 906BT
Gap iiD tool

Before my MD did my front to rear brake pipes, my pedal was soft and spongy with a lot of travel. I tried no end of times to bleed it but it made no difference.
Obviously the MD had to bleed the brakes after replacing the pipes and now the pedal is nice and firm with little travel.
I've heard they use a special bit of kit, whatever that is, so is it worth trying that route for bleeding?
My pedal does sink very very slowly with a hard press.

I can’t think of a logical reason why this should happen but it costs nothing to try.
I changed my pipes a couple of years ago and had similar issues when bleeding the Brakes even with the help of the GAP tool. Got to a point where they were “OK” but still felt a bit soft/spongy/long travel,fine for MOT but didn’t feel right.
A little while later I was playing in the ice and snow using the HDC and ABS and the feel was much better afterwards.
Coincidence? Small bubble trapped somewhere? Definitely not imagination and it costs nowt to try

Ok here we are at this stage, now I have bled the system now 8 times and I am going to take it for a drive in the our fields engage hdc activate the traction control and abs on the slippery ground and see if it settles down,as I said earlier the pedal is normal when engine is off nice and firm , although it does seem better now with the engine running but does still sink eventually , will check back soon with the results , maybe a few days as we have some Machineery infront of the workshop to sort first 1990 3.5 v8 defender
2000 4.6 v8 30th anniversary prins lpg
2004 4.4 v8 vogue prins lpg
2011 4.4 TDV8 Vogue
faultmate extreme
rsw allcoms
Autel 906BT
Gap iiD tool

Go and drive it... You may be surprised to find it's absolutely normal? I've bled some and felt the peddle and thought it went to the floor, only to find it was absolutely normal once on the road sir...

Thanks everyone for your help and suggestions, I certainly will come back with the end results and hope it helps people in a similar situation  1990 3.5 v8 defender
2000 4.6 v8 30th anniversary prins lpg
2004 4.4 v8 vogue prins lpg
2011 4.4 TDV8 Vogue
faultmate extreme
rsw allcoms
Autel 906BT
Gap iiD tool

I agree 100% with what Craig said above.

When I replaced brake pipes and refurbished my calipers I wasn’t happy with how the pedal felt when the car was in the workshop. However, when driving it, the pedal feels great and the brakes work perfectly.

David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior