Impossible to bleed brakes

[Coroner81]

With the MC ports plugged, did the pedal eventually start to sink or was it firm for a good while?

Assuming it held the entire time, I’d use some hose clamp pliers to pinch both rear hoses and see if it firms up. Could be a hose expanding or maybe a cylinder extending too far?

This is a long shot, but may be worth looking at this video. Somewhere in the back of my mind I remember someone having a soft pedal that was remedied this way.

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With the ports blocked, and the truck off, the pedal is rock hard, and doesn't budge. No fade, no movement.
There's only one rear hose on my truck, it's 1 year old, and I'm replacing it tomorrow for poops and giggles just to eliminate something else. There's definitely an air issue, and not just a soft pedal. I keep getting streams of bubbles while bleeding, and the pedal will not pump up and build pressure at all. I'll check out the video in a few when my better half is done watching her stuff on TV. Thank you

Not trying to be a dick, but, my brakes work and yours don't. I'd try gravity bleeding it, especially since you said that you have removed the abs...

It is a very simple system once the abs is removed. Either you aren't good at bleeding brakes, or you have another bad master cylinder. Gravity bleeding will at least eliminate option 1.

If there are no leaks and no abs - The master is the only place that can allow air to enter.

I'm glad your brakes work. Gravity bleeding won't find where air is getting in. I have no problems bleeding brakes. It's not rocket surgery. The MC is working fine. Plugging the ports results in a rock hard pedal.
I'm going with option 3. Air is getting in the lines. Somewhere.

Air can enter anywhere there's a fitting. Not just at the MC. And yes, it was bench bled until piston travel didn't exceed 1/8".

2 pf my bleeder screws were corroded, and didn't seal completely when tightening. Didn't notice that right away because everything was wet from bleeding. That could possibly allow air back in while bleeding.

Wheel cylinders are brand new, and have new bleeder in them. I have used teflon on the bleeder, and still get the same issue. This isn't a trickle of small bubbles. This is a long stream of huge bubbles.

 

[east302]

Can you cap a flared end? Wondering if you can disconnect the line at the wheel cylinder and install a threaded cap to see how removing each wheel impacts pedal feel.


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[letitsnow]

I still think that you are over-thinking this. It is a very simple system. As soon as you say stuff like using teflon tape on brakes lines, most people with brake knowledge left the conversation.

 

[Coroner81]

Can you cap a flared end? Wondering if you can disconnect the line at the wheel cylinder and install a threaded cap to see how removing each wheel impacts pedal feel.

I'm not sure I have anything to cap a flare. I can cap the end of the brake hose on one, or both sides. It wouldn't allow me to test the hard lines across the axle, which are both new, but I can test each wheel independently that way.
That's a solid idea, thanks.

I still think that you are over-thinking this. It is a very simple system. As soon as you say stuff like using teflon tape on brakes lines, most people with brake knowledge left the conversation.

How am I overthinking air bubbles while bleeding brakes? I'm beginning to think you haven't even read anything I've written.

To summarize the steps taken:
1. No Teflon was initially used. The entire brake system was installed without the use of Teflon tape. Or any other sealants or tapes. Double flares were used. My couplings are brass, Flared couplings. I am not using compression fittings.
2. Brakes would not bleed properly, kept getting large air bubbles.
3. Used Teflon on brake bleeder to minimize air being pulled between threads.
4. It reduced the amount of small bubbles being pulled in when the bleeder was cracked.
5. When bleeder was opened, I'm still getting large air bubbles.
6. Closed bleeder while still running vacuum to see if air was leaking between the bleeder head and the hose.
7. There were no air bubbles. Therefore, air was not entering that way.
8. Air is still coming from somewhere.
9. I was not leaking brake fluid at fittings, but possibly was sucking in air.
10. I used a little Teflon on the threads to see if there was a reduction in bubbles.
11. Nothing changed. No fluid was leaking. But I was still getting air bubbles.


I don't want to sound like a dick, but what can I say to get you to leave the conversation?

 

[94burbk1500]

I'm not sure I have anything to cap a flare. I can cap the end of the brake hose on one, or both sides. It wouldn't allow me to test the hard lines across the axle, which are both new, but I can test each wheel independently that way.
That's a solid idea, thanks.



How am I overthinking air bubbles while bleeding brakes? I'm beginning to think you haven't even read anything I've written.

To summarize the steps taken:
1. No Teflon was initially used. The entire brake system was installed without the use of Teflon tape. Or any other sealants or tapes. Double flares were used. My couplings are brass, Flared couplings. I am not using compression fittings.
2. Brakes would not bleed properly, kept getting large air bubbles.
3. Used Teflon on brake bleeder to minimize air being pulled between threads.
4. It reduced the amount of small bubbles being pulled in when the bleeder was cracked.
5. When bleeder was opened, I'm still getting large air bubbles.
6. Closed bleeder while still running vacuum to see if air was leaking between the bleeder head and the hose.
7. There were no air bubbles. Therefore, air was not entering that way.
8. Air is still coming from somewhere.
9. I was not leaking brake fluid at fittings, but possibly was sucking in air.
10. I used a little Teflon on the threads to see if there was a reduction in bubbles.
11. Nothing changed. No fluid was leaking. But I was still getting air bubbles.


I don't want to sound like a dick, but what can I say to get you to leave the conversation?

I'm gonna side with him and say that teflon tape on a flared fitting is dumb as hell. Once you remove abs, the brakes are dead simple. You came here asking for help, trashed the guys suggestion that you didn't try, then decided you need to escalate the situation. He's clearly a more competent mechanic than you but you've decided you don't want to listen to him. If you have air getting in the system but the lines and fittings don't leak then you either have a bad master or bad wheel cylinders, there's only a handful of parts it could be. Don't worry, I am trying to be a dick and I am leaving this thread. Take your truck to a mechanic before you kill yourself or someone else with your incompetence.

 

[Coroner81]

I'm gonna side with him and say that teflon tape on a flared fitting is dumb as hell. Once you remove abs, the brakes are dead simple. You came here asking for help, trashed the guys suggestion that you didn't try, then decided you need to escalate the situation. He's clearly a more competent mechanic than you but you've decided you don't want to listen to him. If you have air getting in the system but the lines and fittings don't leak then you either have a bad master or bad wheel cylinders, there's only a handful of parts it could be. Don't worry, I am trying to be a dick and I am leaving this thread. Take your truck to a mechanic before you kill yourself or someone else with your incompetence.

He suggested my MC was bad. I explained how I tested it, and it's working fine. Being "a more competent mechanic" he then suggested I gravity bleed my brakes. I'm not sure how that would fix air getting in the rear circuit, but yeah, maybe I should sit around for a few hours and try something unrelated to my problem.

I should probably rotate my tires as well. Maybe that'll fix the air getting in.
While I'm at it, I'm going to vacuum the interior, that always helps finding where air is getting in.

I'm not explaining why I decided to use Teflon tape again. I spent a lot of time typing everything that I did, when, and why I did it.

 

[454cid]

I haven't gravity bled the back brakes yet, but it was no problem with the fronts when I changed the calipers. I let the old fluid drain out, as I wanted to change the fluid. I had already sucked out the master with a turkey baster and wiped the reservoir clean. Getting the old fluid to move was the biggest issue... the driver's side didn't move until I cracked open the connection at the hose. When the old fluid stopped draining I removed the old hose, and added new fluid. I connected the new hose to the hard line at some point, and loosely connected the other end to the new caliper. When I got fluid to the far end of the new hose, I torqued it down with the bleeder open. When I got fluid coming out of the bleeder, I closed it, and connected a clear hose, and reopened the bleeder. I got a few bubbles and closed it.... brakes seem fine. It was easy, it was almost like not having to bleed them. It wasn't the horrible ordeal I'd gone through before where I couldn't seem to get rid of bubbles.

 

[AvgJoe]

I own a '94 with over 300k on it now and had the same brake line blow on me. I also replaced the prop valve with what looks like an identical unit to yours. The original had seized internally from the loss of the fluid limping it home. I couldn't bleed my brakes either. Changed m/c (twice), all the lines, wheel cylinders, and calipers. Deleted the RWAL module. I ended up replacing the new universal prop valve with a junk yard unit. There is something amiss with the internal valving that was causing my problem. I even went so far to buy another universal of a different brand. It ended up being the whole problem. I would also lose the teflon tape. Definitely not required on a double flare and may cause more problems. Are you old school bleeding? Power bleeding? I bought both a power bleeder and a vacuum bleeder and still had air until the new (old) valve was installed. If you are old school bleeding and even when bench bleeding the m/c, long and slow. If the brake pedal is pumped repeatedly, you cavitate the fluid in the m/c leading to air everywhere. Long slow strokes of constant pressure and hold. Bleed. Return the pedal. Wait 10 to 15 seconds. I hope this gives you some help as I was in this boat but managed to find a way off. There is a lot of internet "help" out there but unless you find that one person that ran into your specific problem, it is very frustrating. My truck is a '94 so the brakes on mine are very different from yours but at least this may give you some ideas and I'm sure you will find that problem. Keep us informed so it may help someone else!!

 

[Schurkey]

Avoiding drama.

1. I don't suggest vacuum bleeding. You will never get "solid" fluid, there will always be some air. Drum brake wheel cylinders are designed to keep fluid in. They are NOT designed to keep air out. It is overwhelmingly easy to pull air past the seals in a drum brake wheel cylinder, especially if whatever your vacuum device is, generates significant vacuum. This is not a design defect, or substandard parts. It's just the nature of drum brake wheel cylinders. It's also why vehicles with low-mounted master cylinders (brake pedal pivots at the floor, not up under the dashboard) used residual pressure valves to assure that the wheel cylinders never saw vacuum. GM quit using residual pressure valves a few years after they switched to high-mounted master cylinders because having the master cylinder two or three feet above the wheel cylinders provided enough pressure on the wheel cylinder seals.

2. Master cylinders are typically mounted at an angle, with the front "up". They will trap air bubbles that do not bleed out. Until they're positioned level--preferably front "down" a little bit--you'll never get the air out. You say the pedal is hard as a rock with the rest of the system pinched off. Maybe your master is air-free. If, at the end of this, the brake pedal is still soft 'n' low, air in the master is worth investigating. Some guys jack up the rear of the vehicle to tilt the master cylinder "down" in front, other times it's easier to LEAVE THE TUBING CONNECTED, but pull the master off the booster studs and push the front down, then "tickle" the primary piston with a wood dowel or Phillips screwdriver until you don't see bubbles in the compensating ports of the reservoir. Then re-attach the master to the booster, or drop the back end back down.

3. MY procedure is: work at the wheel, I gravity bleed. Work at the master, or major work replacing tubing, or flushing the brake fluid, I use a pressure bleeder. Given the huge quantity of fluid you've already squeezed through the plumbing, and the considerable rework and repairs already performed, I suggest finding a pressure bleeder. Since this has been SUCH a problem-child, I think it would be worthwhile to see if you can create a fluid leak OUT of the system, compared to an air leak INTO the system. This might help confirm that you're just pulling fluid past the wheel cylinders, not past flares or pin-holed plumbing somewhere.

4. I've heard more than one complaint about aftermarket brake valves (proportioning valves, combination valves, etc.) that leak air into the system. "Good used" OEM valves seem to be preferable to brand-new Communist Chinese junk currently sold in the aftermarket.

5. Don't forget to connect the safety switch on your new valve to the dash light when you're done.

 

[Coroner81]

As of Sunday I decided that my 20 years experience of working on cars and trucks wasn't enough, and dropped it off at a shop of a guy who has 40+ years experience. Plus whatever experience his employees have, collectively I'm guessing there's over 150 years experience there. They usually work on normal customer vehicles, but have done work on drag race cars as well.. You know, where brakes are somewhat important.

As of this morning at 10am when I spoke to him, they have been unable to figure it out as well. They just started tearing into it again, and I'll update the thread when I have more information.