I rebuilt my front calipers, rear drums with new wheel cylinders, and replaced some of my lines. While bleeding my brakes the person helping me may have let the master cylinder run dry. We bled the breaks for a couple hours with no progress. We searched everywhere for a leak but nothing showed. We then tried to bleed the abs module and are somewhat confident we did that successfully. After that we spent another couple hours bleeding the breaks with no luck. We tried vacuum bleeding, gravity bleeding, and using the pedal to bleed. My question is why there is still air in my lines and what can be done to fix it?

 

You need to do one brake at a time, farthest from the master first, so right rear, then left rear, then right front, the left front

yes master needs to stay full or you will add more air.

When you push down on the brake pedal do you feel any pressure at all(bleeders closed)?

 

I did do one brake at a time starting from the furthest. The pedal goes to the floor with little break pressure.

 

But there is some pressure at the bottom so master is working?

Then there is no reason it shouldn't bleed out, if you open a bleeder and let it sit open does fluid slowly come out?

You could have an air block, but that is usually not the case when you have a helper pushing down on the brake pedal

 

Yes fluid comes out when I open the bleeder. I think when I put my vacuum bleeder on the bleeder screw it doesn't fit perfectly around it allowing some air to be sucked into my clear tube giving the illusion that there is still a lot of air in my fluid. I think there is an air lock somewhere causing the bad pressure in my braking. Could it be in the master or the abs module? I thought I bled the abs module good enough but I could be wrong. Would my master running dry cause an airlock in there and now I have to bench bleed it?

 

You can reverse bleed

You need correct size tube so it fits snug on bleeder valve, no air leaks

Place container of brake fluid HIGHER than master cylinder, the higher the better.
Put long tube in fluid so it can't slip out but air can get into container so fluid can come out.
Suck on tube or ?? to get siphon started, when there is no air in the tube push it on to the bleeder valve
Open bleeder
Open master cylinder cap, you should see fluid flowing into master and some air bubbles
You can tap on the brake lines and ABS to shake free any air blocks.