Trying to bleed brakes but can't build pressure

[Thundergun]

Hey Guys!

Well i swapped rear ends. i just put an 87 burban rear with posi in my 85 k10 sb.

So i kept the original rear break lines. Installed them into the new drums. Lost a ton of fluid during the swap, naturally.

Filled the reservoir.

Went to do a standard brake bleed but NO PRESSURE will build when we pump the pedal? What the??

Tried to bleed these things from every angle i could think of but no luck. The pedal will not build pressure. There is a little pressure, it's not free wheelin, but it goes all the way to the floor and will not pump up.

I have started the truck several times and tried to pump it up. Actually when it's on, the pedal feels more free or loose, or less resistance.

Help!! i want to fix this tonight! i'm so close!

Thanks!!!

[BADAZ chevy guy]

Two possibilities.
1. Your master cylinder went bad during the swap. (Not real likely)
2. You have to much air in the lines and although it really is building (some) pressure, it isn't enough to feel in the pedal. (Because air compresses and liquid doesn't)
I would try to gravity bleed them. Open one of the bleeder valves, put a pan under it and keep the reservoir full until it stops spitting air. Then move to the rest, one at a time.

[Thundergun]

Awesome thank you sir!

Yes I agree I believe there is a ton of air in the lines because I saw a ton of fluid come out, way more than I would have liked.

Okay so i will just open one of the rear bleed valves, say right rear, and just let it gravity feed until hopefully fluid comes out. I just see that as hard to believe as some of the lines go uphill. The weight of the fluid on the res would have to be enough to drive it all. I wish I had a vacuum pump..

[BADAZ chevy guy]

It's all just physics. Any liquid will find it's own level. As long as the master cylinder is above the wheel cylinder it will work. Just don't let the master cylinder run dry during the process.

[bake74]

Awesome thank you sir!

Yes I agree I believe there is a ton of air in the lines because I saw a ton of fluid come out, way more than I would have liked.

Okay so i will just open one of the rear bleed valves, say right rear, and just let it gravity feed until hopefully fluid comes out. I just see that as hard to believe as some of the lines go uphill. The weight of the fluid on the res would have to be enough to drive it all. I wish I had a vacuum pump..

     You always want to start with the one farthest away from the reservoir, and work your way back to the closest one.  Make sure you do all of the bleeders at each wheel, air will travel to the other wheels even though it will not mix with the fluid, as you pump the brakes you are forcing air to travel the whole system.
      It works well if you have someone who can pump them up several times, then hold the pedal down the whole time you have the bleeder open so no air can come back in, and then repeat until you only get fluid out the bleeder at that wheel.  They also sell kits to do it by yourself that you hook up air to the reservoir (like 2 lbs worth), then you can open and close the bleeders yourself, making sure the reservoir does not run empty as BADAZ chevy guy said.

[Thundergun]

Hey guys. Okay so got full streams of fluid coming out the lines at all 4 wheels. With the vehicle OFF the pedal pumps up great. When I turn the vehicle ON the pedal goes soft again.

Anyone? Buller? Help!!

Thanks!

[bake74]

Hey guys. Okay so got full streams of fluid coming out the lines at all 4 wheels. With the vehicle OFF the pedal pumps up great. When I turn the vehicle ON the pedal goes soft again.

Anyone? Buller? Help!!

Thanks!

     That sounds like a leak between the front and rear in the master cylinder, the fluid has to be going somewhere.  I had the same thing happen to me on one of my 67 cougars.

[BADAZ chevy guy]

If it isn't leaking as bake74 suggested, then the only thing it could be is a bad master cylinder.

[Irish_Alley]

did you bench bleed the cylinder?

[Thundergun]

Hey everyone. Sorry for the delay here. I had to go on travel for 3 weeks for work!

Anyways i was able to get the brakes working properly finally!! I bled everything as instructed starting at the wheel furthest from the cylinder.

The problem, I believe, was a clogged wheel cylinder from debris in the lines. It was impossible to get a full steady stream out as you would expect. We kept at it and i started to see small black particles come through the line and finally full steady streams. Flushed it as thoroughly as we could to make sure no more debris was coming out.

Brakes feel good now.

Thanks for all your help!