Mystery of the unbleedable brakes!

[Ikeaboy1]

My brother and I have been putting in some hours performing various upgrades to my newly purchased Delorean. I decided to replace the flexible brake lines with stainless braided ones supplied by DPI. This kit also came with the stubby caliper hard lines. We replaced them all without much fuss, but cannot seem to get the rear brakes to bleed cleanly. A seemingly never ending stream of bubbles pours out from the bleeders despite at least 3 32oz. Bottles being pumped through the system. The pedal is spongy, of course. The pertinent facts:

-The calipers and master are originals and have 10,000 miles on them
-the brakes functioned perfectly prior to tearing into them
- I've checked all four rear piston actuation. None are seized.
- I've checked and rechecked all rear line fittings. They are all tight.
- the fronts bleed clean
-no leaking fluid anywhere. None. No leaks at the master, any of the lines, the caliper.
- we've varied our bleeding strategy just because we ran out if things to try. We've tried the traditional methods and vacuum bleeding.

Any thoughts on what could be causing so much air to enter the system without any fluid leaking out?

[jackb]

Both rear brakes?
The way I've known to bleed brakes is farthest from the master cylinder->closest. Right rear, left rear, front right, front left.
Since you are getting air at the rear brakes, it must be entering the system ahead of that. Since you said the cylinder and lines are good to go, there has to be an air leak on a fitting somewhere between them. Have you checked the flexible lines? Maybe you can try closing the bleeders, and pumping the brakes- hopefully all the pumping will force fluid out of the spot where air is getting in, and the trouble location will out itself?

[Ikeaboy1]

That is the sequence we attempted. After making no progress with the rear, we decided to try the fronts, which pumped clean almost immediately.

We've gone over and re-tightened every damn fitting on all rear soft and hard lines that we touched. We've also pumped the brakes up with the bleeders closed. Not a drop anywhere. None. It's amazing, and the amount of air coming out is substantial.

Josh just emailed me back and suggested the bleeders themselves may not be seating properly and may be allowing air into the caliper. This is the next thing I'm going to look at.

[Bitsyncmaster]

Are you just seeing little bubbles as you bleed? Some of the bleeder threads suck a little air and if your bleed hose is clear, you will always see those little micro bubbles.

[Ikeaboy1]

No, large pockets of air, not just the tiny fizzy bubbles. The pedal is also not firming up, so if it is the bleeders, they can't just be letting air get pulled downstream , they must be letting a substantial amount being pulled upstream into the system once they're closed.

[David T]

No, large pockets of air, not just the tiny fizzy bubbles. The pedal is also not firming up, so if it is the bleeders, they can't just be letting air get pulled downstream , they must be letting a substantial amount being pulled upstream into the system once they're closed.

Start all over again and bleed the master cylinder. Once you are certain it is done work your way back.

[tommyrich]

Is there any chance that the left/right calipers got mixed up? I saw once (on the fronts) where the owner mixed up the left/right. The bleeders ended up on the bottom and there was no way to bleed the air out. I realize this is unlikely on the rear because of the ebrake, but just thought I would throw that out there.
Tom

[Fox2506]

Forgive me, I skimmed the topic.

None of the calipers have been rebuilt or opened up? There could be sludge in the calipers or lines.

I rebuilt all of my calipers. The front right was filled with sludge. Cleaned it out, flushed it and put them all back together. The front right would no longer bleed properly (fizzy bubbles). My belief is that the same sludge was inside the hardline to that wheel. I'll never know though, because it has all since been replaced.

[Ikeaboy1]

It's freezing cold now and have a sick dog to tend to, so this will have to wait a few days, but I plan on checking all these things when I get back, starting with the master.

The brake calipers themselves I did not touch. The car has had it's brake pads and fluid serviced before by the PO and the fluid came out looking very decent. I'll peek inside the removed lines and see how cruddy they are/aren't.

[BigBenb84]

I had the same issue. I bought the rebuilt caliper, SS flex lines, and new master kit from Hervey. Difference is I didn't use his master because my master was a DMCH one I replaced just 2 years earlier and thought it was ok.

I bled for days, even driving around a spongy pedal to see if it would "work the air out" up to the master or to the caliper to bled later, never happened. Vacuum & pressure bled. I eventually did swap out the DMCH master with one that was with the Hervey kit and after a few bleeds I had firm brakes. His master was bigger then the DMCH one, but I really don't know why the DMCH one wouldn't work. Maybe it was just a coincidence, maybe the act of removing and putting it back into the car fixed it.

[Fox2506]

I'd say it's still possible to have sludge and still bleed clearly. I don't quite remember but it seems like my bleeds were clear at first until the sludge was agitated.

I too had a DMCH master when I had the bleeding issue. after the recent work, though, my pedal is still spongy, as I still have the same master.

[Tillsy]

I'd say it's still possible to have sludge and still bleed clearly. I don't quite remember but it seems like my bleeds were clear at first until the sludge was agitated.

Absolutely - when I first bled mine a year and a half ago I eventually got nice beautiful clean brake fluid.

I then decided to rebuild my callipers anyway just to be anal and this is what was inside each of them:
http://dmctalk.org/attachment.php?attachmentid=12729

[David T]

I'd say it's still possible to have sludge and still bleed clearly. I don't quite remember but it seems like my bleeds were clear at first until the sludge was agitated.

I too had a DMCH master when I had the bleeding issue. after the recent work, though, my pedal is still spongy, as I still have the same master.

Unfortunately flushing the old brake fluid out won't remove sludge. If you have bled well and your pedal is still spongy you might have one or more bad hoses. Have an assistant pump the brake pedal and watch each hose. If it swells up under pressure it must be replaced.

[Fox2506]

Unfortunately flushing the old brake fluid out won't remove sludge. If you have bled well and your pedal is still spongy you might have one or more bad hoses. Have an assistant pump the brake pedal and watch each hose. If it swells up under pressure it must be replaced.

I had a frame resto, and all of my lines and calipers were replaced with SS upgrades. The master is all that remains to my knowledge. It still feels spongy to me like before the resto.

[David T]

I had a frame resto, and all of my lines and calipers were replaced with SS upgrades. The master is all that remains to my knowledge. It still feels spongy to me like before the resto.

If you are confident it is not hoses then my suggestion is to remove the master cylinder, bench-bleed it, and then reinstall and rebleed the brakes.