2004 Sierra Brake Line Replace/Bleed Problem

scottm69s · October 30, 2018

I have a 2004 GMC Sierra 1500 4x4. I just replaced all the rotted out steel lines with stainless steel. The problem I am having is I can not get the lines to bleed fully. The rears are ok and I got most of the air bubbles out but im having trouble with the fronts. I have replaced the lines going down from the master cylinder also. In total I have replaced 6 lines. I have a vacuum bleeder and paperwork with it says not to go over 20psi, so I set it about 15psi and open the bleeder. A little fluid comes out but mostly air. I have been doing this for days and I don't know if just the vacuum takes a very long time to get the air out or if I should take it into a shop and have the master cylinder bleed. Thank you in advance.

SG Lou · October 30, 2018

I had a similar situation when I replaced all of mine on my 04 Silverado 1500 4x4. You may have air trapped in EBCM which is preventing you from getting a good bleed. If you know of someone who has a GM Tech 2 or a Tech 2 clone you can activate the EBCM pump to bleed out the air. I didn't have one at the time so what i did was drive my truck on loose graveled area and hit the brakes hard to cycle the pump. I did that a few times and re-bled the brakes with success.

scottm69s · October 30, 2018

Interesting. Thanks for the tip. I’ll try that tonight.

carnau · October 30, 2018

6 hours ago, scottm69s said:

I have a 2004 GMC Sierra 1500 4x4. I just replaced all the rotted out steel lines with stainless steel. The problem I am having is I can not get the lines to bleed fully. The rears are ok and I got most of the air bubbles out but im having trouble with the fronts. I have replaced the lines going down from the master cylinder also. In total I have replaced 6 lines. I have a vacuum bleeder and paperwork with it says not to go over 20psi, so I set it about 15psi and open the bleeder. A little fluid comes out but mostly air. I have been doing this for days and I don't know if just the vacuum takes a very long time to get the air out or if I should take it into a shop and have the master cylinder bleed. Thank you in advance.

Hey Scott!

One thing I like to do is bottle bleed the system after I replace the lines. I will explain this a little more. Get you a water bottle and make sure it is completely empty. fill it about 1/3 with brake fluid. When bleeding the brakes you always want to go in this order from the furthest from the master cylinder to the closest. So start with the right rear, go to the left rear, then then the right front, the left front, then bleed your master cylinder from the rear to the front.

Now, about the bottle. Get you a piece of vacuum hose (clear if possible) and go to the right rear wheel. Have someone press the brake to the floor one time and hold it to the floor. Then loosen the bleeder screw and watch the fluid come out. Tighten the bleeder screw and do it again until the brake fluid is down to the very end of the hose and then stick in the fluid. Without tightening the bleeder screw anymore (since the bleeder is in the 1/3 of brake fluid) have the person helping you keep pushing the brakes to the floor over and over until you see no air come out. Continue to do this with all of the wheels. Once you have done all the wheels then go back and do a pressure bleed. Pump the brakes until they are very tight and bleed again in the order RR,LR,RF,LF then the Master cylinder. This should get you fixed.

Hope this helps and please be safe. The absolute most important part of a vehicle is the brakes. I don't care how fast you can get to 60... if you can't stop.