Impossible to bleed brakes

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Coroner81

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I made a topic here: https://www.gmt400.com/threads/brakes-wont-bleed.42654/ and cannot delete, or edit it. Apologies for the double post. I thought I had it figured out, but obviously didn't.

I'm sorry in advance for the long post. I tried to cover everything possible.

I can't get my brakes to bleed. I constantly have an almost nonexistent pedal.

1995 Tahoe K1500 4 wheel ABS

I blew the line running to the rear last year. Replaced it, and couldn't get the brakes the bleed. After some reading about the ABS bleeding issues, and not wanting to get screwed at the dealer, (and was unable to safely drive to cycle the ABS) I opted to remove it. It was replaced by a disc/drum proportioning/combination valve.

In doing so, all the lines were replaced last year. Still couldn't get a proper pedal. Blahblahblah

In short, between last year and this year I have replaced the following:

Master. I'm currently on my 3rd. 2 last year, another this year. Bench bled every time until the piston movement didn't exceed 1/8".

Brake booster (to satisfy my fiancés suggestion- I didn't have a hard pedal at all)
All 3 high pressure lines were done last year.
Both wheel cylinders this year.
2 proportioning/combination valves- one last year, and one this year.

Calipers were done 10ish years ago. I tested them Monday with a block of wood, and work fine.

Hard lines on the axle were just done yesterday. I've been using a full size vacuum bleeder (EWK tools), as well as the 2 man BS push and hold, open/close bleeder, release pedal.
I have bled from RR to LF, and have bled LF to RR.

I made fittings with short lines to vacuum bleed the brakes at almost every connection. I bled both ports at the master. Bled all 3 ports from the proportioning valve. Bled the rear right on both sides of the high pressure line where it splits to each axle.
Nothing. Works.

I'm constantly seeing air coming from the rears. I get tiny bubbles up front, and I'm guessing those are air being pulled through the threads of the bleeder. I completely blocked off the rear brakes, and just ran with the fronts, and the brakes are decent.

At the rear I'm seeing huge bubbles. I close the bleeder, let the vacuum build a bit, then crack open the bleeder, and I'm seeing streams of large bubbles. This doesn't stop, no matter how much I bleed. No BS, I have probably run 10-20 quarts through each wheel, (filtering and reusing the old stuff which was purchased this year), since I can't afford to keep buying new bottles. I plan to flush after I have a proper pedal).

I'm losing my MF mind. Any suggestions, dynamite suppliers, locations of high cliffs, etc.. are appreciated.
 

magimerlin

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On your rear brakes... are they adjusted out so that they "just" start rubbing the drum? If not, try that first. You could be over extending the wheel cylinders if the shoes adjusters are all the way in.

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Coroner81

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That's one thing I forgot to mention in my novel. I checked drum clearance prior to installing the wheel cylinders, the drums needed to be persuaded gently with a screwdriver between the drum and backing plate. No serious force, just a slight twist of the blade. This was the same on both sides.

After installing the wheel cylinders, I double checked clearance, and also pressed the pedal lightly to make sure the rear brakes were working, which they are pushing the shoes out, and retracting as they should.

This is why I'm getting so frustrated. I have tried everything I can possibly think of, as well as everything I can find on Google, and my pedal feels like my lines are loaded with air.

Oh and shoes and pads are almost brand new. Maybe a 1/16th thinner than new, if that.​
 

Coroner81

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Just tried bleeding the rears again. I ran 2-2.5 quarts through each wheel, twice. I cleaned the bleeder, wrapped them in teflon, and reinstalled. I bled 2-2.5 qts with the bleeder just cracked 1/8-1/4 turn, and kept getting air. When the bubbles would slow down, I would close, then reopen the bleeder and get a fairly steady stream of bubbles.

I did the same thing with the bleeders open 1/2-3/4 turn, and would get even more bubbles. Closing, then reopening the bleeders created larger air bubbles.
 

smdk2500

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Just a thought when you said all new lines did you replace all the steel lines as well? If not there could possibly be a hole in one of them some where between the prop valve and the rear. If you did replace them might sound like a dumb question but are all the fittings tight. I only ask because ive found that the simplest thing can cause the biggest headache.
 

Coroner81

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All steel lines are new/newer.

I replaced the lines from the MC to the PV last Saturday. Replaced the lines across the rear axle Monday.

The lines from the PV to each caliper were done last year, and are rust free. The line from the PV to the rear high pressure line was done last year, and is also rust free. The fittings on the lines I did last year have mild corrosion/rust, but that's normal here in NY.

Fittings are tight. Fittings were all started by hand, and finished with a wrench. It's why I replaced the lines from the MC to the PV. The flares didn't look clean, and I thought maybe that was the issue, and it wasn't. I used teflon tape on all the lines I redid, to minimize the chance of air being pulled in between the threads, and nothing worked.

If I don't get this figured out by Monday, I might have to swallow my pride and take in it to a shop to have someone else do it.
My truck hasn't been worked on by anyone else in the 10 years I've owned it. I can't even express how frustrated, and disappointed I am.
 
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smdk2500

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Hmm im guessing that all the lines are dry going all the way back. You didn't by chance cross thread one of the fittings and think it was tight and it isn't.
 

Coroner81

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I've been getting fluid through them. The problem is that I'm getting air bubbles as well. I ran about 5 quarts through each of the rears today alone. That's not including what I ran through the rear since I replaced the lines on the axle Monday.

Fittings were all started by hand before I put a wrench on them.
 

smdk2500

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Again dumb question you did get all the fittings tight correct? I ask because ive had that happen. I had some one come up to me and ask me something and I missed righting up one fitting because I broke my concentration. Not saying it happend but might be worth a 2nd look since your getting air in the system from somewhere
 

Coroner81

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The only fitting I haven't checked is where the hard line meets the high pressure hose in the rear, and I can't remember if I used 1 or 2 lines to go to the rear. If I used 2 lines, I'll have a coupling to check as well. I'll check those out tomorrow and report back.

Thanks for the help so far. I appreciate it.​
 
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