l322 range rover braking issue

hi, i have an 2002 l322 range rover td6 that is having braking problems,

it seems like the brake booster is faulty or some other component. after the engine runs for a while. there is plenty of brake pressure. however as soon as the brakes are applied once it seems like it doesn’t regain brake pressure. the brake pedal gets progressively harder until it’s almost rock hard and has barely any braking.

any idea what this could be. it has plenty of brake fluid and i can’t hear any vaccum leaks from inside the car.

could it be the non return valve? or is a servo replacement needed. what checks should i do before replacing the servo


thanks.

One check is to pump the brakes with the engine off and then hold the brake pedal hard down.
Start the engine and it should drop a little as the vacuum increases and pulls the pedal down.
You can also have the servo smoke checked by filling it full of smoke and checking for leaks.
Remove the vacuum line from the servo and start the engine, there should be a draw from the pipe as the vacuum pump starts to do it's job.
Our Volvo has only a limited amount of times the servo helps with the brakes but the system isn't really designed for a collective amount of pedal actions as we normally just use the pedal once to start slowing down.
A cracked or perished diaphragm inside the servo,
A worn vacuum pump,
Split vacuum pipe,
Damaged one way valve..

Mark Piercy said:

One check is to pump the brakes with the engine off and then hold the brake pedal hard down.
Start the engine and it should drop a little as the vacuum increases and pulls the pedal down.
You can also have the servo smoke checked by filling it full of smoke and checking for leaks.
Remove the vacuum line from the servo and start the engine, there should be a draw from the pipe as the vacuum pump starts to do it's job.
Our Volvo has only a limited amount of times the servo helps with the brakes but the system isn't really designed for a collective amount of pedal actions as we normally just use the pedal once to start slowing down.
A cracked or perished diaphragm inside the servo,
A worn vacuum pump,
Split vacuum pipe,
Damaged one way valve..

Click to expand...

thanks for that.

i've done that test and It doesn't really behave normally. as the engine starts. it very briefly goes slightly softer before going rock solid again. if I leave it for 20 seconds or so. then I get a soft brake pedal again. but it will go hard after a single press.

While doing this test, I noticed that if I let the brake vacuum build until I get a soft pedal again. and then press the brakes. it feels normal. but if I keep the pedal depressed. it will slowly push back until all the vacuum is gone and the pedal is hard.

this means that its really quite dangerous when driving and it obviously isn't building pressure fast enough. I would assume a leak in a vacuum line or broken valve?

since it is able to get full brake power briefly. I am reluctant to think that the servo itself has gone. might be naive in saying that though. it doesn't have any lights on the dash, and when scanned for codes. none are present. I would assume this car has some kind of sensor to measure brake vacuum? could be wrong though.

just want to know if anyone has had experience with symptoms like this before.

All most certainly a vacuum leak and it's not like you hear the hiss like an air leak.

So what you really need to know is what's wrong, regardless of others experiences.
Do you have a vacuum pump to check the servo?
Do you have access to a smoke machine?
Have you checked the draw on the vacuum pump?

Mark Piercy said:

So what you really need to know is what's wrong, regardless of others experiences.
Do you have a vacuum pump to check the servo?
Do you have access to a smoke machine?
Have you checked the draw on the vacuum pump?

Click to expand...

Surely the TD6 is a smoke machine ??