Hey everyone,
Been lurking the forum for awhile, but now it is time for me to beg for advice.
I have an 04 Disco with 130,000 km and the worst brakes in the world. On dry roads, I can't get the brakes to lock on engage ABS. I've tried various speeds, up to highway speed with the same result, slowing down gradually.

On snow covered roads, ABS does come on, but still does not slow the vehicle enough.

The other day i was driving down a steep snow covered hill and when ABS came on, the vehicle actually accelerated down the hill (terrifying)

I have changed the pads and rotors (even though the rotors were fine), flushed the brake fluid with some new DOT 4 and bled the system 3 times (no air has ever come out)

To test the booster, I disconnected the vacuum like to the booster and tried the brakes on a slow roll. ALMOST NO BRAKES!! This led me to believe the booster is fine.

Anyone know what's next for me? I've heard about ballooning brake lines, but on inspection, mine looked fine.

I would love some advice as I am terrified to let my wife drive the vehicle for fear that our poor little neighborhood paper boy may not make it home for dinner

 

replace the rubber brake lines i think AB has stainless on sale

 

"On snow covered roads, ABS does come on, but still does not slow the vehicle enough.

The other day i was driving down a steep snow covered hill and when ABS came on, the vehicle actually accelerated down the hill (terrifying)"

This sounds like a problem entirely with your expectations. Sounds like at least in snow, the brakes are working, and you are expecting too much of a 5000lb vehicle on a steep snow covered hill. What kind of tires do you have?

 

I've been fighting a similar issue with mine. I'm not very happy with the performance of the brakes, and I have bled the system thoroughly, including the modulator (thanks to my handy Chinese Autocom+) along with new pads and rotors. I have SS brake lines so I know they're good. It will slow down great on dry roads so long as you aren't in panic mode. If you stomp on them with all you have they won't lock up. I'm still chasing the cause.

 

Put one tire at a time on an ice patch. Seeing the 4WD used TC to slow that tire maybe you could see more that way. If the brakes stop that tire and put power elsewhere you know it is OK. Otherwise yeah, snow plus all the weight on street tires (if that is what you are running) makes for hairy times. Best 4X4 system in the world won't help you with braking. On the 04, in the snow, lock the diff and downshift while braking. Helps lots. Lock diff, low gear and hill decent got me down some crazy bad hills this winter.

 

Did you bleed the ABS unit with a scan tool? You might have air in the ABS portion of the system.

Also, maybe the Master Cylinder has some blockage. It only takes a speck of sand or dirt, etc to block those small passageways.

 

Thanks everyone,
drowssap: I think that's my next step, I've just got to wait till the snow melts to get out on my driveway and replace them.

MarkSF: I don't expect it to stop on a dime, but a vehicle should never accelerate when abs is engaged. I think you misunderstood. I was not sliding down the hill. One wheel began to slip, ABS engaged when regained traction, but the weak brake issue caused my vehicle to accelerate.

SuperSport: No scan tool for the bleed. I did cycle the modulator as I bled however. I'll have to investigate the master cylinder issue more, but if a passageway was blocked, wouldn't I have a hard pedal as a symptom. My pedal feels pretty normal. (not spongy, not too firm)

This is my 4th Disco, and I have never had this issue (I've had every other issue, just not this one) haha

 

but a vehicle should never accelerate when abs is engaged.

Why not? If the force of gravity pulling it down the hill exceeds the available grip, it will accelerate - regardless of the power of the brakes. Very simple physics.

 

Mark,
I think you've misunderstood. Don't worry about it. Btw you just told a physicist "very simple physics" haha. Great job.

 

I think I understand the situation you are speaking of. I had a Chevy S-10 that used to speed up way more than a normal ABS system. It was a programming issue with the ABS system that was recalled. They flashed new software, and it quit doing it.

The one time I ran into it, I had pulled into the Center Divide of the Freeway due to a bad crash on the other side, and I was going to help, but when I hit the dirt, my truck sped up a LOT!!!! It was terrifying, because I knew that was not normal, and I almost ended up in oncoming traffic. Had it been working correctly, I would have stopped with plenty of room.

As far as blockage in the Master Cylinder, I have personally experienced it with my Sand Buggy. It didn't have a hard pedal, it just would not stop sometimes. Almost like it was soft, not hard. Ended up being little flecks of something I could see and was able to clean out. But it didn't have ABS, so probably a different animal completely.