47-55.1 Bad fitting?

[osaltyone]

I am at that point in the build ready to test drive once done bleeding the new brake setup and can’t seem to get this fitting to stop leaking. Any ideas? I’ve had it out so many times, double flare looks good, took some 120grit and tried to smooth it more, but no luck. seems to leak from between the tube and fitting as soon as I pump the brakes twice.

[geezer#99]

You need to mate the flare face with the flare seat in the fitting.
You need to move a tiny bit of metal. To do that just loosen the nut a touch and then tighten it back up. Do that a half dozen times but try to tighten it just a touch more each time. I call that lapping.
If that doesn’t work you might need to replace that tube and fitting and try lapping it to get it to seal.

[mongocanfly]

how does the prop valve side look? can you show pics of it and the end of the brake line? or replace it...

[osaltyone]

Here are some more pics

[mr48chev]

Is that line just the way the flash hit it or is there a mark on the seat?

I see a tiny bit of dirt on the seat in the valve plus what may be uneven marks. That dirt may be enough to cause a leak.

The flare looks pretty good but I'd check it for being absolutely square from one side to the other, My old SnapOn flare tool that I have had for 50 years finally got tired and I was getting flares that looked ok but wouldn't seal on brakes.

[mr48chev]

The blue arrow points to the speck of dirt but the orange arrow points to a mark that matches what may be a mark on the flare of the tube.

[nvrdone]

were these lines the pre bent ones from an auto parts store? I ran into the same kind of problem. turned out that the lines had a metric fitting that just doesnt seal in an sae seat. liked to drive me crazy !!

[dsraven]

check the flare nut to ensure it is square on the end where it contacts and squeezes against the tubing. no cracks or depressions on the end of the nut, so you can be sure it applies even pressure on the flare. the flare is what seals, not the threads etc. the nut is what pushes the flare squarely against the seat.
it may be less work to clean the prop valve cavity with brake cleaner, check the seat for marks, flush it with some fresh clean brake fluid in a syringe or whatever and then replace the line with a new one that hasn't been squashed out yet. if it continues to leak I would suspect the prop valve seat.

[_Ogre]

i'd quit messing with it and re-do the flare. it could be split and you'd never see it.
brake lines are pretty simple, it either works or doesn't. if it doesn't work re-do it
definitely do not use tape of dope on anything related to brakes

[osaltyone]

Originally Posted by nvrdone

were these lines the pre bent ones from an auto parts store? I ran into the same kind of problem. turned out that the lines had a metric fitting that just doesnt seal in an sae seat. liked to drive me crazy !!

These came with the POL brake booster setup for disc/disc I got some months back. I may mess w it a bit more tomorrow and if I can’t get it give them a call Monday. They are just down the freeway from me. I can pull it out of the garage finally once this is done but live on a hill so really need good set of brakes...

If I leave the front line off and have the back right it still moves around so certainly not seating.

I’d bend a new line but I can’t seem to get the flares that good w the manual tool.

[wfojon]

That happened to me with a new master setup, one of the flairs leaked and what I did was use my de-burning tool and smoothed the inside of the flair again and it sealed.
Jon

[MiraclePieCo]

Originally Posted by geezer#99

...loosen the nut a touch and then tighten it back up. Do that a half dozen times but try to tighten it just a touch more each time. I call that lapping.

Geezer's got it. Before you go to extremes, do his loosen/tighten cycle multiple times. I've never had it fail yet. Make sure you're using a tubing wrench so you can really put some torque on it without damaging the fitting.

[mr48chev]

Good quality Tubing wrenches are a must have when your are working with the flare fittings. Tool truck brands or Napa tubing wrenches are something to keep and eye out for when looking though loose wrenches at any kind of sale or pawn shops .

[osaltyone]

Originally Posted by MiraclePieCo

Geezer's got it. Before you go to extremes, do his loosen/tighten cycle multiple times. I've never had it fail yet. Make sure you're using a tubing wrench so you can really put some torque on it without damaging the fitting.

I did change the proportioning valve for a new one still had a leak and tried this method and seems to be ok now.

Now having an issue w bleeding I guess. I have a great pedal nice and solid with the truck off, once I start the truck I can’t hardly get the back wheels to stop and I am on jack stands w no wheels on it. Bled the brakes and see no large bubbles, pretty much just fluid.
Engine is a 5.3, disc/disc setup, speedway gym calipers on the front from the mustang I setup, 8.8 rear with SN 95 new rear calipers. everything new and seems to be fighting me every last step... I’ve bled about 2 large bottles of brake fluid through the system thinking there was a bubble but nothing... any ideas?

[jweb]

You may need the prop valve tool to bleed them properly.
https://www.performanceonline.com/GM...Tool-AC-Delco/

[osaltyone]

Originally Posted by jweb

You may need the prop valve tool to bleed them properly.
https://www.performanceonline.com/GM...Tool-AC-Delco/

Yea, initially I didn’t have that installed but did the last few times. I was thinking the valve might have moved, but read I would not have good stream of fluid if the valve shifted. So went ahead and installed it and still the same.

Couple videos
https://youtu.be/xV9DB1c3aQM
https://youtu.be/rJu5VYuHjR0
https://youtu.be/ZobrH4vXc-A

[jweb]

How’s the pedal once the truck is running?
I had issues with mine and it was the plastic valve on the brake booster that the vacuum line is connected to.
If you remove the plastic valve and try blowing through it air should only go one way. If air goes both ways or not at all, it’s bad.

Also, is it possible you have a disc/drum prop valve?

Are all of your caliper bleeder screws facing up?

[dsraven]

-do you have the valve oriented properly? the port for front brakes actually goes to the front brakes etc? if backwards it may cause issues.
-do you have the master hooked up properly, front brakes are hooked to the correct port etc? is your master cylinder made for disc/disc?
-maybe a faulty valve? they work by limiting brake pressure to the rear brakes so it kinda makes sense if it is faulty there could be limited brake application.
-does the pedal bottom out or does it stop at a decent height but still no rear brakes?
-is the pedal geometry and pedal free play/booster pushrod free play to master cylinder correct so that the master cylinder is getting a full stroke and allowed to return fully when released?
--do you have a frame mounted booster/master cyl? residual valves? some master cylinders have them built into the outlet ports and if your system uses a rebuilt master cylinder you may have obtained one that was originally set up with residual valves in the outlets of the ports, or possibly just one port, for front and rear drum brakes. that could be holding a residual pressure in one circuit so one circuit would possibly require less fluid until they bottom out the pads and build pressure. the other circuit may not be at the same point.
-could the prop valve/combination valve be distorted internally from over torqueing the lines, causing a binding inside?
-do you have a switch terminal midway on the valve, if so, when tested does it show as "turned on"? that would indicate the piston inside the valve has moved, like you have lost brakes to one of the circuits or like you have one of the circuits that has flowed significantly more than the other, so the pressure differential has moved the valve, which would explain your issue of not much brake action to the rear. a "fast bleed" on one of the circuits (rear)may trigger the valve to move which basically shuts off a circuit. there is a link to a site explaining the prop/combi valve with a drawing of the internals.
-have you checked the operation of the brake booster? could the atmospheric valve be faulty or the filter be blocked somehow? does the pedal return fully, is there a built in stop to ensure the pedal returns to the same position/height each time?
-did the system ever function properly? when you say you have a nice firm pedal with engine off, do you also have solidly applied rear brakes as well?
-can you explain what happens after a few pumps of the pedal, engine off. then after the engine is started what does the pedal do? if a hard pedal, if you hold the pedal at a constant pressure, does it slowly fade to the floor? this would indicate an internal leak in the master cyl.
-if you were to look into the master cyl reservoir while a buddly stepped on the brakes, is there a disruption of the fluid at first, like a small fountain of fluid is pushed back into the res, and then with more pedal travel the disturbance goes away and brake application starts? this is because the piston in the bore has to travel back past the cylinder refill ports, when the brakes are released, which allows fluid to replenish the bore as fluid is used or allows extra fluid in the system, caused by heat expansion or whatever, to return to the res. if there is no little fountain at first application of the pedal then maybe the piston is not returning fully. this can be a pushrod travel adjustment between the booster and master or between the pedal and booster or possibly simply because there is no pedal stopper so the pedal height is allowed to change. a changing pedal height can mean the brakes work differently with each application because the master can sometimes not be allowed to return fully.

https://www.motor.com/magazine-summa...nder-selection

https://m.roadkillcustoms.com/test-power-brake-booster/

https://www.freeasestudyguides.com/b...operation.html

https://www.classicperform.com/Instr...akeLineKit.htm

http://mbmbrakes.com/proper-brake-system-plumbing/

[osaltyone]

Originally Posted by jweb

How’s the pedal once the truck is running?
I had issues with mine and it was the plastic valve on the brake booster that the vacuum line is connected to.
If you remove the plastic valve and try blowing through it air should only go one way. If air goes both ways or not at all, it’s bad.

Also, is it possible you have a disc/drum prop valve?

Are all of your caliper bleeder screws facing up?

The pedal feels sloppy. To make the back rotors stop I am literally holding the pedal down w all I can. Pumping doesn’t seem to help when running. Tried bleeding w it running too and no luck.
I’ll check the booster valve tomorrow to see. It’s new but could be faulty. I bought a disc/disc prop valve not site how to tell though.

[dsraven]

The pedal feels sloppy. To make the back rotors stop I am literally holding the pedal down w all I can. Pumping doesn’t seem to help when running. Tried bleeding w it running too and no luck.

seems like you should start at the pedal and work your way through the whole system. ensue the parts are tight, the adjustments are within specs, nothing is binding, etc.
-check the pedal free play
-pedal travel upper stop bumper
-master cyl pushrod end play on the pedal pushrod and also the booster to master cyl
-any and all linkages in the brake pedal to booster to master cyl. is you booster on the firewall or frame?
-check when running, and again when not running and after a few pumps of the pedal to release any stored vacuum in the booter, if there is a small fountain of fluid that can be seen in the master res when the brakes are released after a full hard brake application. there should be 2 fountains actually, one from the front brake circuit and one from the rear. that would let you know if the master is returning fully on both circuits so you know if the circuits are also able to pick up a full shot of fluid for their next application. possibly the booster is moving the pedal pushrod forward when the engine is running so the refill ports in the master cyl are not able to pick up a full charge f fluid.
-do some brake booster diagnostics.
engine off, step on the brakes a coupe of times, use moderate pedal pressure. the vacuum stored in the booster should give you 2 normal feeling applications and then the pedal should start to feel like a non power brake would feel. if less than 2 applications leaves the pedal feeling hard you may have a vacuum leak to deal with.
check the vacuum at the booster, it should be what the vacuum is at the manifold connection. usually this will be around 15-20 inches mercury on the vac gauge. check the hose and the check valve and grommet at the booster plug in. if you have a long hose, like a frame mounted booster, ensure the hose is free of kinks and/or mechanical damage for it's entire length.
once the vacuum is purged from the booster, engine off, step on the brake pedal and hold a moderate application pressure. start the engine while holding the pressure. the pedal should drop slightly.

[dsraven]

do you have some pics of your system? far enough away so we can see what you have to work with?
-pedal style, linkage etc to booster
-booster and master cyl style and mounting location
-any res valves in line
-line connections at master and to prop/combi valve
-a full shot of the truck, it'd be cool to see what you are working on.

here is a quick video (the second link) on how the prop/combi valve operates. it seems like if you had that much pressure applied to your pedal and still have no real brake application to the rear circuit, then maybe the combi valve is locking out the rear circuit due to having sensed a large pressure differential between front and rear circuits while you were bleeding the system. maybe it just needs to be reset to zero again so the piston in the middle (pressure differential valve) is centered. when you bled the brakes did you use the tool to prevent that from happening, where you unscrew the switch and screw in the tool? that's why I asked in a post above if the switch were "turned on" which would indicate the piston isn't where it should be and the rear circuits may be simply locked out. you can easily reset that piston in the pressure differential valve by unscrewing the switch and moving the piston back to center with a clean pointy tool, like a small screw driver, an awl, a long nail etc, something that fits into the small hole at the bottom of the switch etc. use something that isn't painted or that can't flake off a coating when the tool touches the hole or the piston. simply move the piston to center using a prying action, install the switch again and then try your brakes. it might be that simple.

check these videos out for an explanation with cutaways of how the combi valves work and how to tell at a glance if you have the correct valve for a disc/disc system (look at the front of the valve where the front brake lines hook up). the first video shows the differential valve and tool at about the 3 min mark. it explains about the piston and switch I am referring to and also the tool that keeps the valve centered when bleeding. the second is just a video showing the different valves available and what they are for/how they work.

https://www.youtube.com/watch?v=3z1q7MVBs08

https://www.youtube.com/watch?v=dD1dbNtH-6s

https://www.youtube.com/watch?v=qPLaPv8DITE

[dsraven]

if you take the switch out and the groove in the piston is not seen, like it has travelled so far one way you can't see it anymore, you may have to make it move the other way by opening a front bleeder screw (or crack a front brake line at the valve while watching the differential valve piston) and apply the brakes a bit (a buddy helping) so the system senses a pressure differential the other way and the piston moves enough so you can see the groove again. otherwise remove the prop valve section from the rear of the valve and push the piston forward from there using a nice clean tool. the problem with that is you allow air into the system and will have to bleed it again (with the switch tool installed once the valve is centered).

[osaltyone]

Originally Posted by dsraven

if you take the switch out and the groove in the piston is not seen, like it has travelled so far one way you can't see it anymore, you may have to make it move the other way by opening a front bleeder screw (or crack a front brake line at the valve while watching the differential valve piston) and apply the brakes a bit (a buddy helping) so the system senses a pressure differential the other way and the piston moves enough so you can see the groove again. otherwise remove the prop valve section from the rear of the valve and push the piston forward from there using a nice clean tool. the problem with that is you allow air into the system and will have to bleed it again (with the switch tool installed once the valve is centered).

Lots of information! Trying to get through it all. Thank you! I was able to remove the switch and did not see the groove so opened the front caliper pushed the brake pedal and saw and heard it move. I installed the switch and hooked up my test light and the light was lit so removed and did cracked the rear and pushed the pedal. That moved the groove and the test light didn’t light after reinstalling it. I’ll run that wire to my Dakota Digital display later. Do you think I need to bleed again after resetting that valve? Pedal is still the same so I was looking at booster push rod length next but don’t have an easy way to measure that. Not sure if it’s too far out or not enough. POL was supposed to set that when they put it together.
The rear calipers were just replaced with new ones from AUTOZONE since the new/used set I bought a few years back leaked @ the seals. I’ll try to get more pics when I am home later today.

This is the kit I bought with disc/disc setup. Wondering if I should have went with a manual proportioning valve...
https://www.performanceonline.com/19...e-Booster-Kit/


I’ll attach some pics of my setup I have on my phone.

[osaltyone]

Some pics b4 front was on