Brake Question

[1968SWBBigBlock]

Ok heres the story line.
I took out the rear end from my truck. When we put it back in we replaced the lines with new stainless & flex line. We tried bleeding them the old fashioned way pumping the peddle and closing/opening the bleeder. We could not get any fluid. Moved to a one man vaccum pump, got some fluid, maybe 1/3 of a bottle then it stopped. The system would old the Vacuum, but no more fluid would flow. Checked the master cylinder and it still had plenty of fluid. Started looking for pinched lines, pulled the connection off the flex line at the frame, same thing can pull a Vac but no fluid, found the next fitting next to the header under the cab, split the fitting, no fluid, pulled a Vac, it held no fluid.
So whats the problem?
Bad splitter block?
Bad Master Cylinder?
Anything I missed?
I thought the brakes worked fine before but maybe not?

[Ace in the hole]

could it be you have a blockage in one of the lines you replaced? you pulled some fluid past it but then it may have moved and stopped in a bend or some thing. I have never had it with brake lines but I did have a spider or something crawl in a small hydraulic line and block it once, just a thought for you.

[casterbuster]

I just had the same problem when I did my front disc swap... What I had to end up doing was this... I took the rear brake line lose at the proportional valve and slid the end of a snuggly fitting hose over the end of the line.

I then placed the place the hose into a new bottle of fluid and went to the back with my hand pump and pulled fluid into the system until it was completely air free,

Then I went back to the proportional valve and made a line from the outlet of the valve and ran it into the bowl of the master cylinder. I used clear plastic hose hear which is very important. I actually did this for both the front and the rear at the same time... Then I sat in the truck and pushed the pedal in as far as it would go and held it.. You should be able to see your lines from the gap between your hood and your cowl. You will notice while the pedal is down there will be air bubbles in your hose going into the bowl... Now this is very important slowly begin releasing the brake, but not so fast that the bubbles pull back into the proportional valve, if you release slow enough it will pull fluid underneath the bubbles back into the valve... the next time you push the pedal...push it a little harder, or quicker and hold it again the fluid should push some of the of the bubble into the the bowl which will let it escape...release the pedal slowly again... repeat these steps until all of the air is out of the mastercylinder and the proportional valve... then hook your lines up and and bleed them normally... Make sure your bowls never go dry... Or you will have to start all over

[kbs71]

There is a pin that sticks out of the front of the prop valve. that needs to be pushed in to properly bleed the rear brakes. It holds the residual valve open for fluid to by pass.

[Orange]

Originally Posted by casterbuster

I just had the same problem when I did my front disc swap... What I had to end up doing was this... I took the rear brake line lose at the proportional valve and slid the end of a snuggly fitting hose over the end of the line.

I then placed the place the hose into a new bottle of fluid and went to the back with my hand pump and pulled fluid into the system until it was completely air free,

Then I went back to the proportional valve and made a line from the outlet of the valve and ran it into the bowl of the master cylinder. I used clear plastic hose hear which is very important. I actually did this for both the front and the rear at the same time... Then I sat in the truck and pushed the pedal in as far as it would go and held it.. You should be able to see your lines from the gap between your hood and your cowl. You will notice while the pedal is down there will be air bubbles in your hose going into the bowl... Now this is very important slowly begin releasing the brake, but not so fast that the bubbles pull back into the proportional valve, if you release slow enough it will pull fluid underneath the bubbles back into the valve... the next time you push the pedal...push it a little harder, or quicker and hold it again the fluid should push some of the of the bubble into the the bowl which will let it escape...release the pedal slowly again... repeat these steps until all of the air is out of the mastercylinder and the proportional valve... then hook your lines up and and bleed them normally... Make sure your bowls never go dry... Or you will have to start all over

This sounds right - although it isn't exactly what I did - it is effectively the same thing.

I had the same problem with the fronts on mine actually.
I had bench bled my master cylinder, and also had a new prop valve and to it. For whatever reason the M/C air-locked on the front pod.

What carterbuster is describing is bench bleeding the master cylinder with the prop valve attached, while on the truck. Honestly, this should probably be done with the prop out of line (just come out of the M/C ports back into the bowls), but his testimony is proof it will work otherwise I suppose.

I tried pushing the pin in and everything else - but to no avail. Re-bleeding the master is all that got me bleeding the system again.

DLB

[casterbuster]

Well, before I did this... I had bench bled the master by itself several different times. This was my last resort and what do you know it worked.

[Orange]

Originally Posted by casterbuster

it worked.

Case and point.

DLB