If both MC's are the same, then and they are both doing the same thing I would start by pulling the sticky caliper. And see if sticks when it is off the Disco, if the pistons are moving freely check the guide pins. Then try just bleeding that one caliper, and go big get lots of fluid out.

After that if it is still acting up a pressure test would be the way to go, just check all 4 corners to start and get a base line, here is a general link to the process https://www.brakebleeder.com/pressur...st%20vehicles.

 

One other thing that right rear takes a lot to get right due to the line length you could give it another go same thing go big 1/2 can of fluid big on the bleed.

 

Thanks Richard.

I was just looking at another thread on similar issue and the OP posted about the rod from Booster having a black fitting on the end, like a rubber grommet or something. Any idea if the booster rod has anything on the end? I've checked my spare and there is nothing. But this would explain not getting pressure on initial pedal travel.

 

suspect normal pressure under braking should be about 1500-2000 psi or so....I don;t have LR specific numbers. But if you see 500 under pressure, that is too low....

sorry, missed that the calipers were replaced. And some of the hard lines. I had a similar situation with another vehicle. Everything replaced except some of the hard lines. I had no brakes. I suspected that there was rust inside the hard lines that were not replaced. There is no brake equalizer valve, so that is not it. The ABS pump is a flow through design so it should not restrict flow.

the fact that the fronts are hot is worrisome for a cause described by another disco forums member, the MC push rod was not installed correctly or had shifted causing constant pressure.

You said the pedal sinks to the floor when engine running sooooo...
1) you DO have vacuum
2) possibly the lines are NOT full of fluid (even if bled to hell...I like using the vacuum bleeder hand held system)
3) MC could still be at fault

I bleed the ABS block by having someone pump the MC, hold it, then loosening the hard lines and watch for fluid. Tighten the fitting while still leaking out and not before releasing the pedal . repeat.

I know the frustration of this. I have been fighting a brake pull on my black disco for a while.....

 

I am in Canada, Ontario. Do you have something like a Upull such as kennys upull or picNsave. They are on the web. Anyhow if you do go to something like that go and get a abs unit and a Master cylinder. Substitute first master and see if there is a difference, then the abs unit. If you here hissing with the engine off its the booster or lines to or check valve. My 2000 has weak brakes but thats due to old flex lines. It travels 2 miles a week the rest of the time its parked as I go trucking in my 29000 lb volvo so I will get to it, one day. lol I have heard of a guy that by past all abs stuff and connected one wheel only, to test if the master and booster worked. He said if that one wheel held he knew it was the abs unit.

 

oh I assume you have a copy of RAVE and bleeding the brakes in the correct order.

 

Sounds like a possible bad brake booster to me.

 

as @MrHSE7 noted it could be the booster that is the only thing you did not replace here is a link to testing https://axleaddict.com/auto-repair/B...-Booster-Check I know you have checked some of the vacum but for the cost of a tool rental and some basic tests it is worth getting out of the way.

 

I've actually replaced the booster. No love there.

Here's what I believe to be the issue:
When I first got the truck, I bled the lines since the PO had let it run dry, at least the MC res. Hey presto, we had brakes. But since I thought the MC was the cause of the leak I replaced it. Since then No Brakes. I spoke with someone today that believed about 6-12 months ago there was a bad batch of MCs that had a high failure rate. And also that my unit would have TRW markings if truly TRW. Since that change I've never had a positive brake pedal unless pumped 2 or 3 times. Based upon that I ordered another proper MC from reputable source. As previously stated, I cannot find the receipt nor any indication of the provenance of this MC. So we will see how this goes.

Thanks for the post thus far. I promise to keep the forum posted.

 

Looking forward to what happens with a new MC