did you actually take apart the calipers and replace the pistons and seals?
" I tracked that down to a blown stub axle seal, but replaced the caliper pistons and seals for good measure,"
I ask b/c this is fairly odd to do vs replace the caliper as a whole.

have you made sure all your lines are clear?
"The pedal bleeding had pushed old corrosion to the point of blocking the outlet and no fluid was getting out of the master cylinder."
If I had found this (granted this is the interwebs - I dont know the severity of the corrosion) I would have disconnected all lines and purged with compressed air.

Good luck

 

I didn't split the calipers if that's what your asking. I had already ordered a piston and seal kit, thinking that was the issue for the fluid on the rotor, prior to discovering the blown stub axle seal. Since I already had the kit, I decided I might as well do that while I was in there. The seal and piston replacement is a fairly simple job and much cheaper than replacing the entire caliper. Judging by the fact that the front driver's caliper seals actually went a few weeks later and they were very brittle when I pulled them, it was about time for that job anyway. I have kits on order for the two remaining calipers now, although there are no visible leaks yet. With those, I just ordered the seals, as the pistons that have come out of the other calipers clean up just fine.

Between the MC change and the two caliper services, I've run over two liters of new fluid through the system, evenly distributed between all 4 calipers. Everything comes out clear and with the pressure bleeder method, I can't see any line not being clear at this point.

To be honest, I hadn't been sure of what had caused the issue initially. I had just tracked it down to the MC. I had already replaced the reservoir to MC seals with the Audi ones a few months prior when they started to leak. So, I was just over that part and wanted a new one. It wasn't until after I pulled it that I was able to identify the exact issue. It had leaking seals between the MC and servo as well though, so would have had to be rebuilt even if I cleared the interior. Just wasn't worth it to me.

Thanks for the well wishes.

 

So, it sounds like Im ordering a brake proportioning valve at this point. Does anyone have a preferred supplier for those?

I've seen a few new ones on Ebay: Britpart, AP, All Makes for around $130. Otherwise, Atlantic British, Roverland and Rovers North are all in the $180-$200 range. I haven't seen any good quality used ones on Ebay in the last few days.

Let me know if anyone has any suggestions. Thanks everyone.

 

British parts of Utah have served me well in the past.

 

Thanks very much. I checked them out.

Before plunging ahead with the order, I had a long talk on Friday afternoon with the lead mechanic at Atlantic British. His assessment was as follows.

1) ABS air - Bleeding the ABS wouldn't be the issue. Any air introduced into the module through the standard bleeding of the bad master cylinder could also be removed with standard bleeding, which I've done in spades. If there happened to be air in the system that could only be removed by activating the system, then it would only present when the system activated, not consistently as is my issue. Additionally, air in the system in general would not present with a sinking pedal, but one that requires pumping to firm up (we noted this earlier in the thread). If the ABS is the issue, it would be an internal hydraulic leak between chambers or one presenting where I'm not seeing it. In either case, the unit would need to be replaced, as it's non serviceable.

2) Hydraulic - This is where he felt the root cause would be. Without visible leaks, he believed there were 4 possible explanations. 1) Hydraulic expansion or minimal leak (not yet visible) in the rubber system parts: caliper piston seals or rubber brake lines. 2) Pass through issue of the internal seals in the master cylinder 3) Seal leak internal to the brake servo 4) Internal leak between chambers of the ABS module.

So, here is the action plan and the results to this point.
1) Isolate the MC and servo from the rest of the brake system and test. I pulled the two brake lines and plugged with two bolts and o-rings to allow them to seat. With this set-up the pedal was completely firm and did not descend. So, the MC and servo should be officially ruled out and the issue further down stream.
2) I've ordered new seals for the remaining two calipers which I hadn't repaired yet, along with stainless steel brake lines. If figure those would be the logical next step. Simply because even if they don't solve the issue, it's still a good idea and not wasted money.
3) If the problem persists following that, it would seem I'm looking at the ABS. Although, prior to replacing that, I will isolate the system to the MC, servo and brake reduction valve. If the system presents there, then It would seem to be the ANR3194 valve after all.

Thanks very much for all the help, I'll keep everyone updated.

 

Just an update. I received all the parts finally yesterday. The brake hoses were the last to arrive, shipping from NY. So, the work will begin this weekend:

Replace rear caliper piston seals
Replace front caliper piston seals
Replace rear rubber brake lines
Replace front rubber brake lines

While I'd love to bleed the system after each individual repair and then test to give a definitive answer on which, if any of those items solve the issue, I'm too lazy for that. So, I'll report back once it's all done.

 

I finally got the chance this week to do the planned work. I replaced the pistons in seals in the remaining two calipers and installed stainless lines front and rear. Then I pressure bled all four calipers twice, going through roughly 1.25 liters of brake fluid in total. The rubber lines I removed all seemed fine, with no cracks or leaks. I did find a bit of jellied brake fluid between the wiper seal and fluid seal on one of the pistons in the rear caliper, indicating a minor leak.

The results of all the repairs was an increase in actually braking power, but no change in the performance of the pedal. I can still drive it to the floor under constant pressure and stopping power takes much longer pedal travel than it should. Pumping up the pedal does nothing to increase the pedal firmness, indicating that the system is clear of air.

I did a short road test where I took the temperature off all four rotors prior to driving and then again afterwards, with frequent braking. Prior to the drive, all rotors read at 67 degrees. After, both fronts were around 200 degrees. The right rear was 120 and the left rear 90. I'll retest tomorrow to see if I get the same discrepancy in the rear. If so, I guess it could mean an ABS module failure that's relieving pressure from that caliper? Although I don't feel the ABS engaging.

Bottom line, is I'm still at a loss and chasing the issue

 

Do you have a copy of the Service Manual (the Rave)? Normally when bleeding the brake system with ABS you have to activate the modulator using Test Book. Since that isn't applicable there are other ways to activate it. Two wire hydraulic motor, one's Red and the other is Brown, Red's positive, Brown is negative...... battery voltage. It will **** a bunch of fluid through whichever caliper bleed you have open so I'd suggest a switch in your hand to operate the motor with. I haven't done it but I would if I still had my Disco and my Jeep does need new fluid so if I can't find a cheap program to run the ABS pump then I'll backwoods it just like I mentioned.

One thing about pedal under steady pressure going to the floor is the booster which you haven't addressed. They can leak like anything else on a Rover, not fluid but vacuum/air pressure. You've changed the MC, you've bled the lines, there are no leaks so the booster is the next logical step in the manual. Just saying, not pin pointing it. Did you change the proportioning valve yet? The weak back caliper may be air in that portion of the line, I'd use a pressure bleeder to push it out. Takes two liters with a pressure bleeder, that's stated in the manual as well. Your about a 1/2 liter shy.......

 

I’m a person that used to play some musical instruments and I noticed that the steps are almost always on the beat of the song. That’s when I decided to count to the beat (1-2-3-4) in my head. This helped a TON. On the harder difficulties where there would be many steps in a short amount of time, I would add eighth notes to my counting (1 and 2 and 3 Nox Vidmate VLC and 4 and) and those steps were almost perfectly on beat as well.