Suggestions For Getting Air Out of the Brakes - Chevy and GMC Duramax Diesel Forum
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post #1 of 9 (permalink) Old 12-31-2019, 07:33 PM Thread Starter
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Suggestions For Getting Air Out of the Brakes

So I finally got around to replacing my leaky hydrobooster. I am now wishing I would have put it off for a couple more days, after the 1st. I tip my hat to all the people on the forum that have described the task as "simple." On paper it seemed simple to me but boy was it a pain. So I know many people are able to change out the booster without removing the master cylinder. I honestly don't know how that is possible on the LML, I could not make the room I needed. So I just removed the brake lines from the cylinder (mistake) and took it off too. Well my new hydrobooster seems to be working, its not leaking. But my brakes have no pressure and will obviously need to be bled... alot. I can not get the pedal to be stiff at all. I lost all the fluid out of the cylinder and reservoir when I had it off, of course I filled it all the way up before attempting to bleed the brakes. And no I did not bench bleed the MC before install, as I did not know of the process until researching later. I bled each caliper multiple times but have not seen any air actually come out. So I am guessing the air is trapped in the lines or cylinder and hasn't made its way to the calipers yet (need more DOT 3 and too cold and dark). I plan to pick this up tomorrow (if they are open):

https://www.harborfreight.com/brake-...AaAqxzEALw_wcB

And just run fresh DOT 3 until all the air and old fluid comes out. Am I missing anything? Any other suggestions? Truck has not been drove, just cranked to run the power steering pump and get the air out of the new booster. As of right now, the brake pedal goes all the way to the floor with ease.

2011 LML Silverado 2500HD CCSB Z71, Leveled, Bagged, AFE DFS780 Lift Pump, B&W Companion.
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post #2 of 9 (permalink) Old 01-01-2020, 09:54 AM
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Since you already removed the master cylinder once and there is air in it, just remove it again and bench bleed it. You will not get a complete air bleed without doing it on a bench, the pedal travel is not enough.

2005 LLY 3500 CCLB 215,000 miles
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post #3 of 9 (permalink) Old 01-01-2020, 10:30 AM
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The last time I flushed my brakes, I had a hell of a time. I hadn't used the bleeder for a long time and forgot about the instructions and thought I knew what I was doing. I don't remember exactly what I was doing wrong but when I finally got frustrated enough to review the instructions and follow them, it worked like a champ. Worst part was that there's a sticker right on the tank with instructions and I didn't even notice.

I've gotten air out of the MC with my pressure bleeder after running it dry but it will take a lot of fluid. If your using a pressure bleeder make sure you don't drop below 35 psi. I run mine at around 40-45 psi. It would be helpful if you had someone to watch the pressure for you. The instructions with my bleeder say to open the bleeder screws 10 seconds at a time with key off.

This is the bleeder I have. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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post #4 of 9 (permalink) Old 01-01-2020, 10:48 AM
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Actually, here's a link to the full instructions. I don't think it's specific to this particular bleeder but just to pressure bleeding in general.

https://www.redlinestands.com/manual...%20Bleeder.pdf
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post #5 of 9 (permalink) Old 01-01-2020, 03:09 PM
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I canít add anything to the topic of bench bleeding, but to get the air out of the top vertical end of the two lines to the MC you can loosen the line nuts. Do this after the bench bleed and with the pedal up. Gravity should allow the air to leak out of the loosened line nuts, and flow fluid to the bottom to replace the air.
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post #6 of 9 (permalink) Old 01-04-2020, 01:55 PM Thread Starter
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Thank you for all the tips and suggestions. Unfortunate I got sick right after this happened and I have not been able to give the truck my full attention. I was able to spend a few hours bleeding the brakes with the bleeder I posted the link to. I saw all the old fluid come out, followed by a ton of air, then new fluid, with still some air bubbles. I was not able to put the time in to get all the air out before I got sick. I am leaving for vacation tomorrow (luckily in my wife's truck) so my truck is being dropped off at my mechanic so he can bleed the brakes and ABS controller while I am gone. Thanks again for the tips!

2011 LML Silverado 2500HD CCSB Z71, Leveled, Bagged, AFE DFS780 Lift Pump, B&W Companion.
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post #7 of 9 (permalink) Old 01-04-2020, 07:02 PM
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With that bleeder, you will see a continual stream of bubbles after clean fluid flows....it's sucking air thru the loose threads on the bleeder valve. Normal.

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post #8 of 9 (permalink) Old 01-06-2020, 05:20 PM
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Quote:
Originally Posted by Hook'em_Horns! View Post
With that bleeder, you will see a continual stream of bubbles after clean fluid flows....it's sucking air thru the loose threads on the bleeder valve. Normal.
Adding to this, putting thread sealant or grease on the threads will prevent air from getting past the threads. Helps determine when air is truly pulled from the line, and not the threads.

2005 LLY 3500 CCLB 215,000 miles
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post #9 of 9 (permalink) Old 01-13-2020, 03:22 PM Thread Starter
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Quote:
Originally Posted by Hook'em_Horns! View Post
With that bleeder, you will see a continual stream of bubbles after clean fluid flows....it's sucking air thru the loose threads on the bleeder valve. Normal.
Thanks for that info Hook

I am still on vacation and will be for the next week or two. But my mechanic worked on my truck last Monday. He bench bled the MC and bled the lines. Says all is good now. I feel very confident that I could have got it myself if I would have had the time, but oh well. He also went ahead and gave me a new brake tag as mine was out of date

2011 LML Silverado 2500HD CCSB Z71, Leveled, Bagged, AFE DFS780 Lift Pump, B&W Companion.
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