Brake problem

We have a discovery 2 2003 TD5. My wife said the brake pedal was spongy. I have bled the brakes and the pedal is solid, until I switch the engine on and then the pedal goes right down slowly with steady pressure. Is this a servo problem or does it mean that a power bleed with hawkeye or Lynx is needed?

When you say

brianconwy said:

pedal goes right down slowly with steady pressure.

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Do you mean to the floor?

Cheers

With the engine off the pedal feels nice and firm and applies the brakes with firm pressure on the pedal. No sponginess even with sustained pressure.

With the engine on the brakes work but the pedal is soft and will eventually go to the floor with sustained pressure.

If there is no fluid loss. Look at the fluid tank. Get someone to press the brake with engine running and see if level in tank rises. With the engine stopped and no vacuum you may not be able to apply enough pressure to make the master cylinder nrv bleed back. But the extra pressure exerted by the servo may cause nrv bleed back. If that is the case the master cylinder needs to be looked at.

I have just tried this and no change of level in the reservoir at all. I was almost hoping there would be.

find a longer slope select low + HDC and let it make it's job(if you dont have experience with HDC read the driving and operating guide in the owner's handbook), if it works as it should IMO the master cylinder is gone.... what's good is that if HDC gets into action the system will back bleed itself and at least you know there's no air left in it

I will go and try that now. Thanks.

I took it to the top of the Sychnant Pass and let it descend in 1st gear with HDC button pressed. It seemed to go down fine but an amber warning light came up on the right which according to the manual is the off-road height adjustment. I may have pressed that button by mistake because at one point I stopped to let another car pass.

Working HDC is evidence of well working system(from electronic and hydraulic point of view) so IMO the master cylinder is the prime suspect

I have ordered one. Is manual brake bleeding ok or is a powerbleed with a diagnostic tool needed?

keep the pipe verical and refill it with a syringe, bleed the cylinder alone before you refit the pipe to it then go and make HDC work and no bleeding is necessary...anyway, as long as the modulator doesnt get empty no need for power bleed