Brake pedal goes straight to the floor

[andytats]

im have a problem with the Landy ( get the joke's out off the way. Yes the big problem is its a disco and im the driver of it lol )
the brake pedal went straight to the floor
now have a hard pedal with engine off, pedal goes straight to the floor when the engine is running.
So today I put in new brake pads all round
It don't have any leaks. If I pull the vacuum hose off the servo the pedal doesn't drop. Put my finger over the hose and it has good suction. Put it back on the servo pedal goes to the floor.
I will try bleeding it tomorrow. Just wondered if anyone has any other ideas on what could be wrong with it.

[gregster]

It could well just be a case of bleeding them Andy...The servo assistance will increase the braking pressure, so it is conceivable that you could have a hard pedal but when the engine starts the extra pressure applied is sufficient to compress the air in the system which would cause the pedal to drop.
Certainly worth trying a bleed like you are suggesting in the first instance mate...

[Rifleman]

Sounds like the servo or the one way valve mate.

[Renegade]

I reckon I can hold off on the jokes given the situation
gregsters right about bleeding em if you sure of no leaks.
A few questions that might help:
How worn were the brakes? As the piston moves out as the brakes wear, it takes more fluid and just might have drained the resevoir, bringing some air with it. Very rare though and takes a combination of four quite worn sets of pads and discs with an initally slightly lower brake fluid level.
Did this happen before or after the brake work?
On some cars (Yes, I'm looking at you, Vauxhall!!) Pushing the piston back without opening the bleed nipple runs the risk of inverting a seal in the master cylinder. This allows all the fluid you push towqrd the brakes when breaking to return when you release the pedal. This increases the distance between the pad and disc aswell as allowing fluid to rush past the seal making the pedal travel to the floor, or near as one side of the tandem collapses while the other works. With the engine off the force exerted by the pedal is actually not enough to make the now useless seal fail right away, and you can pump up a nice hard pedal for yourself. If that happens, the only option is to get a seal set or replace the cylinder assembly.
Lastly, the daft question as I'm not sure around servos them selves. I get how they use vacuum to work, but is there some kind of limiting device in them to stop them from over working? Could that fail meaning a new servo? Sorry for the story, should probably work on shortening them
And very finally.. What number and combination of letters adorns the bonnet of your truck? Some say there is a certain combination that's literally the death of any vehicle unlucky enough to have it..... I know Renault is one. There are a small few others....

[Renegade]

Yes, like Rifleman

[2much]

Hi Andy,

Might not be a load of help but key points to check for me (after leaks), not neccessarily in this order!

- Brake bias valve (if fitted) at rear could be letting by. With servo disconnected you cant get enough pressure to push fluid past seat - with connected you can. I had this on my old 2.3 after chasing everything round the car several times!!

- Brake master cyclinder - for same reasons as above. Could you test by seeing what braking power you have when driving (safely ) on road with servo disconnected. If brakes work then more likely servo?

- Servo - but i cant see how it could be this as i thought they either work or dont(?) and i dont think there is any interaction between fluid side and vacuum side other than mechanical link via. diaphram but maybe some sort of NRV prevents the pedal pressure forcing vacuum back into pump/tank? therefore the pedal is moving not beacuse of hydraulic compresseion but on vac' side

Regarding leaks they can be v.difficult to find as sometimes the pipe is actually slightly porous and the fluid sweats out rather that sprays/drips. The one on my current truck took a while to find....

[2much]

again not sure if this helps but sounds like a similar problem here

http://www.fronteraowners.co.uk/forums/viewtopic.php?f=23&t=52516

might be worth keeping in touch to share ideas??

[andytats]

Thanks for the help I bleed the system but still the same then I replaced the m/c then new fluid and bleed it again. it's a little better so I will try bleeding it again at the weekend

[Renegade]

Andy, get a friend to sit on the brakes with the engine running. And look at every flexi pipe for bulges under pressure. Happened today at work, very soft pedal on a shed of a kangoo, Adjusted the rear drum brakes a while back. Improver a little but today it was the same. Upon pressing the pedal hard, the front left pipe f*ckin bulged right out!! Couldn't believe it he was so lucky.. So were we!

Definitely something worth trying

[andytats]

Thanks for that mate all pipes have been checked