HELP cant get my brakes back

Changed discs and calipers (all new) on rear of my 98 Disco tdi and bled them.

Problem is now that I cant get a pedal without pumping it a couple or three times.

1. I have bled all four corners and put half a gallon of fluid through it.

2. There is no air in the system only pure new fluid.

3. I have tried changing the master cylinder and it is still the same.

4. There is no fluid loss and the pedal does not sink once pumped a few times

If I pump the pedal three times with the engine running I get brakes and the pressure does not drop off, I can leave my foot pressing the brake for as long as I like and it does not fall away.

If I then leave the brakes alone with the engine running for a minute and then press the pedal it goes to the floor and then pumps up again.

Same with the engine off and no servo assist, pump three times and pedal rock solid, leave it a minute and press again and it goes straight to the floor.

No leaks and no air in it, no ABS , cant understand it.

Please help as I need the Disco desperately

Did you bleed the odd extra points on the callipers that don't look like bleed nipples?

is fluid splashing in mnaster cylinder when pedals pumped ,occaisionally servo rod needs adjusting ,some new calipers may need checking for slight leaks ,and are pads loose ive had some were piston was pulled back in instead of staying against pad meaning they wernt self adjusting had to fit new pistons and genuine seals

jamesmartin said:

is fluid splashing in mnaster cylinder when pedals pumped ,occaisionally servo rod needs adjusting ,some new calipers may need checking for slight leaks ,and are pads loose ive had some were piston was pulled back in instead of staying against pad meaning they wernt self adjusting had to fit new pistons and genuine seals

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Can they truly be that bad?

Should ask why did you change them? Was it cos you had to pump the pedal or just old age?

yes spent ages bleeding everywhere ,adjusted rod to the point brakes pulled on with servo ,but noticed pads where looser than expected ,pistons were going back after letting pedal up ,luckily had a new set of pistons and seals ,but usually is m/c or air

Brakes worked fine before with no pumping etc.

Rear pads worn out and calipers badly corroded so put new discs pads and calipers on.

Rear calipers working ok and adjusting ok.

I'm thinking that I may have disturbed the master cylinder seals when I bled the brakes and that the other master cylinder may be the same but not sure

I'm told it will be the servo but cant understand why the same thing happens when servo depleted and brakes tried without engine running.

I've been caught out with air on the things, luckily non of the other issues

Can only find one bleed nipple on front caliper (at the top)

On old master cylinders, they sometimes do damage if they go past their normal travel, ie when you bleed them and go straight to the floor. Doesn't sound like the servo to me, if the servo is empty you should have a really hard pedal that won't pump up. How have you bread it?

m/c would seem most likely have a look in res when someone pedal,definately not servo

From memory the nipples are 11mm certainly on the rear there's an extra 10 mm what looks like a bolt but it has a taper on the bottom of it, I slacken that and usually find air under it? If its basically blead you can take it out and gravity will draw fluid through it when it overflows with no sign of air put it back and rebleed normally can't remember if the fronts have them, I did exactly the same to a disco a few months ago, did as above and no dramas!

jamesmartin said:

m/c would seem most likely have a look in res when someone pedal,definately not servo

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OK ta I'll also check the old master cylinder to see if any fluid has passed the seals.

Diesel Do said:

On old master cylinders, they sometimes do damage if they go past their normal travel, ie when you bleed them and go straight to the floor. Doesn't sound like the servo to me, if the servo is empty you should have a really hard pedal that won't pump up. How have you bread it?

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Bled it first time on the pedal with engine off.

Second time with easy bleed at below 20psi, put over a quarter of a gallon of fluid through it that time.

Diesel Do said:

From memory the nipples are 11mm certainly on the rear there's an extra 10 mm what looks like a bolt but it has a taper on the bottom of it, I slacken that and usually find air under it? If its basically blead you can take it out and gravity will draw fluid through it when it overflows with no sign of air put it back and rebleed normally can't remember if the fronts have them, I did exactly the same to a disco a few months ago, did as above and no dramas!

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If its not the master cylider then there must be a LOT of air somewhere and I'm surprised that the pedal isn't spongy

It's difficult to say when you're not there, if it's really that bad I'd probably start with the mc too,

Diesel Do said:

It's difficult to say when you're not there, if it's really that bad I'd probably start with the mc too,

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I've had a look at the master cylider that I took off and it looks to be ok, seals intact and not too worn.

Drfove it today and there are brakes but the pedal goes right down to the floor almost.
Just a little pump gives a little more pedal but good brakes.

I'm wondring if the servo may be at fault after all.

Priced up a master cylindr today an it was 165 quid

Got another master cylinder in my spares box so will try that first.

old used m/c is likely to be poor ,did you try to see if it splashed fluid ,black deposit on the bottom of res ,servo only helps you press pedal ,

jamesmartin said:

old used m/c is likely to be poor ,did you try to see if it splashed fluid ,black deposit on the bottom of res ,servo only helps you press pedal ,

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yes, a little black on bottom of resevoir.

would the mc failure be due to disturbance do you think?

a tried and trusted way before you bin the master cylinder is
tap with a hammer, press pedal, release pedal, tap with hammer and repeat while bleeding brakes.
The master cylinders can fail on changing fluid if worn and air gets in, but also the seals can stick when pushed further than normal travel.

if when pumping the brake fluid starts going black your mc is toast

Also if you fit a new mc prime it before the pipes are put on or your have a devils job trying to bleed it

Not to call you stupid but have you put the rear calipers on the right side and are the bleed nipples are on the top of the calliper. The reason I ask as my mate bought a disco and the brakes were displaying the same problems that you are having. Upon inspection I noticed the rear callipers were fitted on the wrong side and were also upside down so the bleed nipples was facing down. After refitting and bleeding the brakes were perfect.