Brake lines not gettin the juice.....

[Slick67]

Cannot get the fluid to go to the back brakes. Typical disc/drum setup. I did have the rear line higher than the prop valve but fixed that. Air is coming out the rear bleeders when the pedal is compressed but no fluid. I bench bled the master cyl. All new lines, no crimps in the lines and all seems right. Any thoughts??

[cdowns]

lots of guys neglect clamping the pin on the combination valves as instructions in the factory service manual states as the proper way to bleed these brakes

[Slick67]

Originally Posted by cdowns

lots of guys neglect clamping the pin on the combination valves as instructions in the factory service manual states as the proper way to bleed these brakes

Clamping the pin? Is that the pin on the back of the prop valve? My rear brake hose comes out toward the front of the truck, and there is a pin on the back.

[68gmsee]

If you're postively sure that you're not sucking in air from somwhere like a loose connection or crack in the brake lines or rubber hoses (two in front, one in rear) then it could be just a lot of air in the lines. Be sure and not let the master cylinder get low on fluid when bleeding. I usually add fluid over 2 full depressions of the brake pedal.

Also you can loosen the fittings at the master cylinder and work yourself back to see if you can isolate it.

[Myself]

I had that exact same problem on one earlier this summer. The safety valve in the proportioning block will switch to one side if there is a problem with front OR rear. I ended up having to just really smash the pedal while my wife tapped on the prop block with a hammer. After a bit we heard a popping noise and pressure was restored to the rear. This was all due to a leaking brake line to the rear.

[mrein3]

Originally Posted by cdowns

lots of guys neglect clamping the pin on the combination valves as instructions in the factory service manual states as the proper way to bleed these brakes

I believe that holding that pin in overrides the safety feature that diverts fluid away from a failed half of the brake system. You may have the tripped this system and will need to make the tool the service manual describes to hold the pin to get your brakes bled.
Posted via Mobile Device

[Slick67]

Alright! Some great suggestions here! My girlfriend watched the thread for me today and called me with updates, what a chick. First issue I discovered was that the lines were backwards from the MC to the Prop valve (see above pic). Also had a couple of connections that were not sealed well. Got all of these problems fixed and bled the system. Had brakes for a little while then they faded. The pedal is still bottoming out and I can't get the front passenger side to bleed out properly. More suggestions???

[PHAT TONY]

I've had to put a cheapy hand vacuum pump with a hose on the rear lines to the wheel cylinder at the wheel cylinder and draw fluid to the back, and yes; it may empty the master.

[Slick67]

Originally Posted by PHAT TONY

I've had to put a cheapy hand vacuum pump with a hose on the rear lines to the wheel cylinder at the wheel cylinder and draw fluid to the back, and yes; it may empty the master.

Tried a vacuum yesterday with little success. Finally got some fluid to run through every line, but not a steady stream. I had the front working and before I left the shop it had no front brakes. The back brakes never did work. All of the lines have been seperated at the connectors and new teflon tape put on. Back to square one? Is there something that I am missing?

[truckdude239]

stop why did you put teflon tape on the fittings???? the brake lines a re flare fitting that are self sealing. if you put teflon tape on the fitting they will elak and not seal correctly. i'd pull the fittings and remove all the teflon tape and tighten everything back up and go from there

[mrein3]

Originally Posted by Slick67

Tried a vacuum yesterday with little success. Finally got some fluid to run through every line, but not a steady stream. I had the front working and before I left the shop it had no front brakes. The back brakes never did work. All of the lines have been seperated at the connectors and new teflon tape put on. Back to square one? Is there something that I am missing?

No tape on flare fittings! Did you try holding that pin while bleeding?
Posted via Mobile Device

[pat 70/71]

shouldn't need teflon tape anywhere in a brake system. (flare fittings) Did you change out all the front hoses? old ones can get blocked over time. re bleed the master& open up one wheel cylinder at a time starting @ pass rear & push new fluid shouldn't take too long . could master be bad? hope this helps. cheers, Pat

[Slick67]

Originally Posted by truckdude239

stop why did you put teflon tape on the fittings???? the brake lines a re flare fitting that are self sealing. if you put teflon tape on the fitting they will elak and not seal correctly. i'd pull the fittings and remove all the teflon tape and tighten everything back up and go from there

Originally Posted by mrein3

No tape on flare fittings! Did you try holding that pin while bleeding?
Posted via Mobile Device

I did use teflon tape but just one round and only on the threads at the top of each connection. There is no teflon tape close to the end of the threads at the flared end. Is that still a no-no to do that?

[Slick67]

The pin that is on the prop valve needs to be pushed in while bleeding but is it free floating or does the hex head around it need to be loosened?

[mrein3]

Originally Posted by Slick67

The pin that is on the prop valve needs to be pushed in while bleeding but is it free floating or does the hex head around it need to be loosened?

You just push the button. The manual gives measurements for a 'tool' you can make to bolt to the valve and hold the pin down.

[mrein3]

Here ya go. Make yourself a J-23709...

[Slick67]

Ok. Made a tool and pushed the pin in and bled all of the brakes again. No luck. Any other suggestions?? I am running out of options and starting to thing that the booster/master or the prop valve is bad.

[packers05]

start with the master, make some plugs for the fluid ports, bleed it with them, if the pedal is up and rock hard move on to next front calipers , watch for a good stream when opening bleeders, also watch pistons to be sure a pad is not stuck allowing to much piston travel, should only move 1/16" , next pull drum and be sure shoes are adjusted tight enough and cylinders are not stuck.

[Slick67]

I have bench bled the master twice, no bubbles at all. I have went through the process several times with no change in the pedal. I pushed the pin in today, no results. After the second time there was front brakes, then they faded away. The back brakes have yet to grip good enough to keep from moving the tire by hand. I do have a good stream on the back. The front calipers are not getting enough fluid to push the pistons, or even stop the tire from free spinning. The pedal just goes to the floor with no preassure. WHAT AM I MISSIN HERE?!?!?! I will take off the drums tomorrow and check out the cylinders and tightness of the pads. Any other suggestions other than take it to a shop??

[VA72C10]

bump for answers because I don't have any

[mrein3]

I have seen cases where the "check ball" piece in the proportioning valve got stuck. This is evident by the brake light getting stuck on. With the pin clamped and enough bleeding and some gentle taps on the valve I was able to center it again.

Is your brake light on? Does the brake light work?

Are your back brakes adjusted properly? The shoes should slightly drag with no pressure on the brake pedal. With the rear tires in the air I like to adjust the rears until there is some resistance in the spinning wheel.

Have your girlfriend get in the driver's seat and push HARD with both feet on the brake pedal while you run around and look at EVERY connection for leaks.

That is all I can think of right now.

[stich626]

if you have a pedal than it's gone, you have a leak somewhere, thats allowing air back in..

is there any cracks in the flares?
if you made lines you did double flare..
you did use copper washers at the front disc calp to rubber line bolt..
the master could be sucking in air.. you blead the master , and plug the ports with plugs ( they make flare nuts with no hole for the line, (or make two)
got a pedal, good walk away.. in an hour does it?
if so the master fine..
next,, sounds line you have a crushed line,, that slowly let fluid therough, and you get a petal. then it slowly bleads out to the rrest of the line. and then no petal..
good luck.

[Slick67]

Originally Posted by mrein3

I have seen cases where the "check ball" piece in the proportioning valve got stuck. This is evident by the brake light getting stuck on. With the pin clamped and enough bleeding and some gentle taps on the valve I was able to center it again.

Is your brake light on? Does the brake light work?

Are your back brakes adjusted properly? The shoes should slightly drag with no pressure on the brake pedal. With the rear tires in the air I like to adjust the rears until there is some resistance in the spinning wheel.

Have your girlfriend get in the driver's seat and push HARD with both feet on the brake pedal while you run around and look at EVERY connection for leaks.

That is all I can think of right now.

I will check the brake lights. The rear drums are easy to spin but they do have a little friction. I can adjust those a little tighter I think and will do that today. There are no leaks at all, I have checked this over and over. The check vavle sounds like a reasonable problem since I had brakes on the front, then they faded. Well....off to the shop for another round with "sancha". Thanks for the bump VA and mrein3 for all of the great help, I appreciate your patience and keeping up with this thread. Once it is fixed I will post the answer to the problem.

[mrein3]

Originally Posted by Slick67

I will check the brake lights. The rear drums are easy to spin but they do have a little friction. I can adjust those a little tighter I think and will do that today. There are no leaks at all, I have checked this over and over. The check vavle sounds like a reasonable problem since I had brakes on the front, then they faded. Well....off to the shop for another round with "sancha". Thanks for the bump VA and mrein3 for all of the great help, I appreciate your patience and keeping up with this thread. Once it is fixed I will post the answer to the problem.

Sorry I wasn't more clear. Make sure the brake warning light in your dash works and is not on. If the bulb is burnt out you may not know if your prop valve is stuck to one side. I believe that when you turn ignition key on it should light up. Then ground the wire on the prop valve and confirm that this lights that lamp.

[my67c20]

First is everything plumbed correctly? From the photo it appears you have the front bowl plumbed to the rear output of the prop valve and the rear to the front output. It would also appear that the front bowl is the larger and should be plumbed to the front brakes.

http://67-72chevytrucks.com/vboard/s...d.php?t=184148

I looked thru your build thread (nice work) and it was hard to see everything around the prop valve and master cylinder. Some pictures would be nice.

Second do you have a long enough push rod in the master cylinder? Sometimes over looked.

Understand how those vacuum pumps work. Basically you create a vacumn in a bottle and when you open the bleeder it sucks stuff out, Only after doing this for hours will you effectively pull all the air out if the air is near the bleeder. A pressure bleeder is by far the best tool for forcing fluid thru the lines to create a steady stream.

Third adjust the rears until they really drag good. Remember spinning the wheel by hand and feeling a drag is different than a 3500lb vehicles idea of dragging.

How much of this bleeding has been done with the vehicle running and pulling a vacumn?

I suspect by your statement earlier on that the peddle fades leaves me to believe your master cylinder has some bad seals, or a plumbing problem

Did you buy the master chromed or did someone do it out for you?

Did you release the check valve after you bled and before you tested the system?

If you have no leaks you are 50% on your way.